8 subject: Introduction to ksh-93 date: January 14, 1993
9 Charge Case 311531-0101
10 File Case 49059-6 from: David G. Korn
23 ksh-93 is a major rewrite of ksh, a program that serves as a
24 command language (shell) for the UNIX* operating system.
25 As with ksh, ksh-93 is essentially compatible with the
26 System V version of the Bourne shell[1] , and compatible
27 with previous versions of ksh. ksh-93 is intended to comply
28 with the IEEE POSIX 1003.2 shell standard and the ISO 9945-
29 2[2] shell standard. In addition to changes in the language
30 required by these standards, the primary focus of ksh-93 is
31 related to shell programming. ksh-93 provides the
32 programming power of several other interpretive languages
33 such as awk[3], FIT[4], perl[5], and tcl[6].
35 This memo assumes that the reader is already familiar with
36 the Bourne shell. It introduces most of the features of
37 ksh-93 relative to the Bourne shell; both as a command
38 language and as a programming language. The Appendix
39 contains a sample script written in ksh-93.
52 * UNIX is a registered trademark of USL
56 BELL LABORATORIES PROPRIETARY
57 Not for use or disclosure outside Bell Laboratories except by
58 written approval of the director of the distributing organization.
74 subject: Introduction to ksh-93 date: January 14, 1993
75 Charge Case 311531-0101
76 File Case 49059-6 from: David G. Korn
91 The term "shell" is used to describe a program that provides
92 a command language interface. Because the UNIX* system
93 shell is a user level program, and not part of the operating
94 system itself, anyone can write a new shell or modify an
95 existing one. This has caused an evolutionary progress in
96 the design and implementation of shells, with the better
97 ones surviving. The most widely available UNIX system
98 shells are the Bourne shell[7], written by Steve Bourne at
99 AT&T Bell Laboratories, the C shell[8], written by Bill Joy
100 at the University of California, Berkeley, and the KornShell
101 language [9], written by David Korn at AT&T Bell
102 Laboratories. The Bourne shell is available on almost all
103 versions of the UNIX system. The C Shell is available with
104 all Berkeley Software Distribution, BSD, UNIX systems and on
105 many other systems. The KornShell, is available on System V
106 Release 4 systems. In addition, it is available on many
107 other systems. The source for the KornShell language is
108 available from the AT&T Toolchest, an electronic software
109 distribution system. It runs on all known versions of the
110 UNIX system and on many UNIX system look-alikes.
112 There have been several articles comparing the UNIX system
113 shells. Jason Levitt[10] highlights some of the new
118 * UNIX is a registered trademark of USL
122 BELL LABORATORIES PROPRIETARY
123 Not for use or disclosure outside Bell Laboratories except by
124 written approval of the director of the distributing organization.
140 features introduced by the KornShell language. Rich
141 Bilancia[11] explains some of the advantages of using the
142 KornShell language. John Sebes[12] provides a more detailed
143 comparison of the three shells, both as a command language
144 and as a programming language.
146 The KornShell language is a superset of the Bourne shell.
147 The KornShell language has many of the popular C shell
148 features, plus additional features of its own. Its initial
149 popularity stems primarily from its improvements as a
150 command language. The primary interactive benefit of the
151 KornShell command language is a visual command line editor
152 that allows you to make corrections to your current command
153 line or to earlier command lines, without having to retype
156 However, in the long run, the power of the KornShell
157 language as a high-level programming language, as described
158 by Dolotta and Mashey[13], may prove to be of greater
159 significance. ksh-93 provides the programming power of
160 several other interpretive languages such as awk, FIT, perl,
161 and tcl. An application that was originally written in the
162 C programming language was rewritten in the KornShell
163 language. More than 20,000 lines of C code were replaced
164 with KornShell scripts totaling fewer than 700 lines. In
165 most instances there was no perceptible difference in
166 performance between the two versions of the code.
168 The KornShell language has been embedded into windowing
169 systems allowing graphical user interfaces to be developed
170 in shell rather than having to build applications that need
171 to be compiled. The wksh program[14], provides a method of
172 developing OpenLook or Motif applications as ksh scripts.
174 This memo is an introduction to ksh-93 the program that
175 implements an enhanced version of the KornShell language.
176 It is referred to as ksh in the rest of this memo. The memo
177 describes the KornShell language based on the features of
178 the 02/25/93 release of ksh. This memo is not a tutorial,
179 only an introduction. The second edition of reference [9]
180 gives a more complete treatment of the KornShell language.
182 A concerted effort has been made to achieve both System V
183 Bourne shell compatibility and IEEE POSIX compatibility so
184 that scripts written for either of these shells can run
185 without modification with ksh. In addition, ksh-93 attempts
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189 Not for use or disclosure outside Bell Laboratories except by
190 written approval of the director of the distributing organization.
206 to be compatible with older versions of ksh. When conflicts
207 between these versions of the shell, ksh-93 selects the
208 behavior dictated by the IEEE POSIX standard. The
209 description of features in this memo assumes that the reader
210 is already familiar with the Bourne shell.
215 There is no separate command language. All features of the
216 language, except job control, can be used both within a
217 script and interactively from a terminal. However, features
218 that are more likely to be used while running commands
219 interactively from a terminal are presented here.
223 By convention, UNIX commands consist of a command name
224 followed by options and other arguments. Options are either
225 of the form -letter, or -letter value. In the former case,
226 several options may be grouped after a single -. The
227 argument -- signifies an end to the option list and is only
228 required when the first non-option argument begins with a -.
229 Most commands print an error message which shows which
230 options are permitted when given incorrect arguments.
231 Ordinarily, ksh executes a command by using the command name
232 to locate a program to run and by running the program as a
233 separate process. Some commands, referred to as built-ins,
234 are carried out by ksh itself, without creating a separate
235 process. The reasons that some commands are built-in are
236 presented later. In nearly all cases the distinction
237 between a command that is built-in and one that is not is
238 invisible to the user. However, nearly all commands that
239 are built-in follow command line conventions. In addition,
240 the option sequence -? causes the command to print a usage
241 message which lists the valid options.
243 ksh has several options that can be set by the user as
244 command line arguments and as option arguments to the set
245 command. Most options can be set with a single letter
246 option or as a name that follows the -o option. Use set -o
247 to display the current option settings. Some of these
248 options, such as interactive and monitor (See Job Control
249 below) are enabled automatically by ksh when the shell is
250 connected to a terminal device. Other options, such as
251 noclobber and ignoreeof are normally placed in a startup
254 BELL LABORATORIES PROPRIETARY
255 Not for use or disclosure outside Bell Laboratories except by
256 written approval of the director of the distributing organization.
272 file. The noclobber option causes ksh to print an error
273 message when you use > to redirect to a file that already
274 exists, If you want to redirect to an existing file, then
275 you have to use >| to override the noclobber option. The
276 ignoreeof option is used to prevent the end-of-file
277 character, normally ^D(Control-d), from exiting the shell
278 and possibly logging you out. You must type exit to log
279 out. Most of the options are described in this memo as
284 Command aliases provide a mechanism of associating a command
285 name and options with a shorter name. Aliases are defined
286 with the alias built-in. The form of an alias command
289 As with other shell assignments, no space is allowed before
290 or after the =. The characters of an alias name cannot be
291 characters that are special to the shell. The replacement
292 string, value, can contain any valid shell script, including
293 meta-characters such as pipe symbols and i/o-redirection
294 provided that they are quoted. Unlike csh, aliases in ksh
295 cannot take arguments. The equivalent functionality of
296 aliases with arguments can only be achieved with shell
297 fucntions described later.
299 As a command is being read, the command name is checked
300 against a list of alias names. If it is found, the name is
301 replaced by the alias value associated with the alias and
302 then rescanned. When rescanning the value for an alias,
303 alias substitutions are performed except for an alias that
304 is currently being processed. This prevents infinite loops
305 in alias substitutions. For example with the aliases,
306 alias l=ls 'ls=ls -C', the command name l becomes ls, which
307 becomes ls -C. Ordinarily, only the command name word is
308 processed for alias substitution. However, if the value of
309 an alias ends in a space, then the word following the alias
310 is also checked for alias substitution. This makes it
311 possible to define an alias whose first argument is the name
312 of a command and have alias substitution performed on this
313 argument, for example nohup='nohup '.
315 Aliases can be used to redefine built-in commands so that
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321 Not for use or disclosure outside Bell Laboratories except by
322 written approval of the director of the distributing organization.
338 can be used to look for test in your current working
339 directory rather than using the built-in test command.
340 Reserved words such as for and while cannot be changed by
341 aliasing. The command alias, without arguments, generates a
342 list of aliases and corresponding alias values. The unalias
343 command removes the name and text of an alias.
345 Aliases are used to save typing and to improve readability
346 of scripts. Several aliases are predefined by ksh. For
347 example, the predefined alias
348 alias integer='typeset -i'
349 allows the integer variables i and j to be declared and
350 initialized with the command
353 While aliases can be defined in scripts, it is not
354 recommended. The location of an alias command can be
355 important since aliases are only processed when a command is
356 read. A . procedure (the shell equivalent to an include
357 file) is read all at once (unlike start up files which are
358 read a command at a time) so that any aliases defined there
359 will not effect any commands within this script. Predefined
360 aliases do not have this problem.
364 When run interactively, ksh saves the commands you type at a
365 terminal in a file. If the variable HISTFILE is set to the
366 name of a file to which the user has write access, then the
367 commands are stored in this history file. Otherwise the
368 file $HOME/.sh_history is checked for write access and if
369 this fails an unnamed file is used to hold the history
370 lines. Commands are always appended to this file.
371 Instances of ksh that run concurrently and use the same
372 history file name, share access to the history file so that
373 a command entered in one shell will be available for editing
374 in another shell. The file may be truncated when ksh
375 determines that no other shell is using the history file.
376 The number of commands accessible to the user is determined
377 by the value of the HISTSIZE variable at the time the shell
378 is invoked. The default value is 128. Each command may
379 consist of one or more lines since a compound command is
380 considered one command. If the character ! is placed
381 within the primary prompt string, PS1, then it is replaced
382 by the command number each time the prompt is given.
386 BELL LABORATORIES PROPRIETARY
387 Not for use or disclosure outside Bell Laboratories except by
388 written approval of the director of the distributing organization.
404 A built-in command named hist is used to list and/or edit
405 any of these saved commands. The option -l is used to
406 specify listing of previous commands. The command can
407 always be specified with a range of one or more commands.
408 The range can be specified by giving the command number,
409 relative or absolute, or by giving the first character or
410 characters of the command. When given without specifying
411 the range, the last 16 commands are listed, each preceded by
414 If the listing option is not selected, then the range of
415 commands specified, or the last command if no range is
416 given, is passed to an editor program before being re-
417 executed by ksh. The editor to be used may be specified
418 with the option -e and following it with the editor name.
419 If this option is not specified, the value of the shell
420 variable HISTEDIT is used as the name of the editor,
421 providing that this variable has non-null value. If this
422 variable is not set, or is null, and the -e option has not
423 been selected, then /bin/ed is used. When editing has been
424 complete, the edited text automatically becomes the input
425 for ksh. As this text is read by ksh, it is echoed onto the
428 The -s option causes the editing to be bypassed and just
429 re-executes the command. In this case only a single command
430 can be specified as the range and an optional argument of
431 the form old=new may be added which requests a simple string
432 substitution prior to evaluation. A convenient alias,
434 has been pre-defined so that the single key-stroke r can be
435 used to re-execute the previous command and the key-stroke
436 sequence, r abc=def c can be used to re-execute the last
437 command that starts with the letter c with the first
438 occurrence of the string abc replaced with the string def.
439 Typing r c > file re-executes the most recent command
440 starting with the letter c, with standard output redirected
445 Lines typed from a terminal frequently need changes made
446 before entering them. With the Bourne shell the only method
447 to fix up commands is by backspacing or killing the whole
448 line. ksh offers options that allow the user to edit parts
449 of the current command line before submitting the command.
452 BELL LABORATORIES PROPRIETARY
453 Not for use or disclosure outside Bell Laboratories except by
454 written approval of the director of the distributing organization.
470 The in-line edit options make the command line into a single
471 line screen edit window. When the command is longer than
472 the width of the terminal, only a portion of the command is
473 visible. Moving within the line automatically makes that
474 portion visible. Editing can be performed on this window
475 until the return key is pressed. The editing modes have
476 editing directives that access the history file in which
477 previous commands are saved. A user can copy any of the
478 most recent HISTSIZE commands from this file into the input
479 edit window. You can locate commands by searching or by
482 The in-line editing options do not use the termcap or
483 terminfo databases. They work on most standard terminals.
484 They only require that the backspace character moves the
485 cursor left and the space character overwrites the current
486 character on the screen and moves the cursor to the right.
487 Very few terminals or terminal emulators do not have this
490 There is a choice of editor options. The emacs, gmacs, or
491 vi option is selected by turning on the corresponding option
492 of the set command. If the value of the EDITOR or VISUAL
493 variables ends with any of these suffixes the corresponding
494 option is turned on. A large subset of each of these
495 editors' features are available within the shell.
496 Additional functions, such as file name completion, have
499 In the emacs or gmacs mode the user positions the cursor to
500 the point needing correction and inserts, deletes, or
501 replaces characters as needed. The only difference between
502 these two modes is the meaning of the directive ^T. Control
503 keys and escape sequences are used for cursor positioning
504 and control functions. The available editing functions are
505 listed in the manual page.
507 The vi editing mode starts in insert mode and enters control
508 mode when the user types ESC ( 033 ). The return key, which
509 submits the current command for processing, can be entered
510 from either mode. The cursor can be anywhere on the line.
511 A subset of commonly used vi editing directives are
512 available. The k and j directives that normally move up and
513 down by one line, move up and down one command in the
514 history file, copying the command into the input edit
515 window. For reasons of efficiency, the terminal is kept in
518 BELL LABORATORIES PROPRIETARY
519 Not for use or disclosure outside Bell Laboratories except by
520 written approval of the director of the distributing organization.
536 canonical mode until an ESC is typed. On some terminals,
537 and on earlier versions of the UNIX operating system, this
538 doesn't work correctly. The viraw option, which always uses
539 raw or cbreak mode, must be used in this case.
541 Most of the code for the editing options does not rely on
542 the ksh code and can be used in a stand-alone mode with most
543 any command to add in-line edit capability. However, all
544 versions of the in-line editors have some features that use
545 some shell specific code. For example, with all edit modes,
546 the ESC-= directive applied to command words (the first word
547 on the line, or the first word after a ;, |, (, or &) lists
548 all aliases, functions, or commands that match the portion
549 of the given current word. When applied to other words,
550 this directive prints the names of files that match the
551 current word. The ESC-* directive adds the expanded list of
552 matching files to the command line. A trailing * is added
553 to the word if it doesn't contain any file pattern matching
554 characters before the expansion. In emacs and gmacs mode,
555 ESC-ESC indicates command completion when applied to command
556 names, otherwise it indicates pathname completion. With
557 command or pathname completion, the list generated by the
558 ESC-= directive is examined to find the longest common
559 prefix. With command completion, only the last component of
560 the pathname is used to compute the longest command prefix.
561 If the longest common prefix is a complete match, then word
562 is replaced by the pathname, and a / is appended if pathname
563 is a directory, otherwise a space is added. In vi mode, \
564 from control mode gives the same behavior.
568 It is possible to intercept keys as they are entered and
569 apply new meanings or bindings. A trap named KEYBD is
570 evaluated each time the user enters a key from the keyboard,
571 except while entering a search string or an argument to an
572 edit directive such as r in vi-mode. The action associated
573 with this trap can change the value of the entered key to
574 cause the key to perform a different operation.
576 When the KEYBD trap is entered, the .sh.edtext variable
577 contains the contents of the current input line and the
578 .sh.edcol variable gives the current cursor position within
579 this line. The .sh.edmode variable contains the ESC
580 character when the trap is entered from insert mode of vi
581 mode. Otherwise, this value is null. The .sh.edchar
584 BELL LABORATORIES PROPRIETARY
585 Not for use or disclosure outside Bell Laboratories except by
586 written approval of the director of the distributing organization.
602 variable contains the character or escape sequence that
603 caused the trap. The value of .sh.edchar at the end of the
604 trap will be used as the input sequence.
606 Using the associative array facility of ksh described later,
607 and the function facility of ksh, it is easy to write a
608 single trap so that keys can be bound dynamically. For
612 trap 'eval "${Keybind[${.sh.edchar}]}"' KEYBD
613 function keybind # key seq
615 Keybind[$1]=".sh.edchar=${.sh.edmode}$2"
621 The job control mechanism is almost identical to the version
622 found in csh of the Berkeley UNIX operating system, version
623 4.1 and later. The job control feature allows the user to
624 stop and restart programs, and to move programs to and from
625 the foreground and the background. It will only work on
626 systems that provide support for these features. However,
627 even systems without job control have a monitor option which
628 when enabled, will report the progress of background jobs
629 and enable the user to kill jobs by job number or job name.
631 An interactive shell associates a job with each pipeline
632 typed in from the terminal and assigns them a small integer
633 number called the job number. If the job is run
634 asynchronously, the job number is printed at the terminal.
635 At any given time, only one job owns the terminal, i.e.,
636 keyboard signals are only sent to the processes in one job.
637 When ksh creates a foreground job, it gives it ownership of
638 the terminal. If you are running a job and wish to stop it
639 you hit the key ^Z (control-Z) which sends a STOP signal to
640 all processes in the current job. The shell receives
641 notification that the processes have stopped and takes back
642 control of the terminal.
644 There are commands to continue programs in the foreground
645 and background. There are several ways to refer to jobs.
646 The character % introduces a job name. You can refer to
647 jobs by name or number as described in the manual page. The
650 BELL LABORATORIES PROPRIETARY
651 Not for use or disclosure outside Bell Laboratories except by
652 written approval of the director of the distributing organization.
668 built-in command bg allows you to continue a job in the
669 background, while the built-in command fg allows you to
670 continue a job in the foreground even though you may have
671 started it in the background.
673 A job being run in the background will stop if it tries to
674 read from the terminal. It is also possible to stop
675 background jobs that try to write on the terminal by setting
676 the terminal options appropriately.
678 There is a built-in command jobs that lists the status of
679 all running and stopped jobs. In addition, you are informed
680 of the change of state (running or stopped) of any
681 background jobs just before each prompt. If you want to be
682 notified about background job completions as soon as they
683 occur without waiting for a prompt, then use the notify
684 option. When you try to exit the shell while jobs are
685 stopped or running, you will receive a message from ksh. If
686 you ignore this message and try to exit again, all stopped
687 processes will be terminated. In addition, for login
688 shells, the HUP signal will be sent to all background jobs
689 unless the job has been disowned with the disown command.
691 A built-in version of kill makes it possible to use job
692 numbers as targets for signals. Signals can be selected by
693 number or name. The name of the signal is the name found in
694 the include file /usr/include/sys/signal.h with the prefix
695 SIG removed. The -l option of kill provides a means to map
696 individual signal names to and from signal number. In
697 addition, if no signal name or number is given, kill -l
698 generates a list of valid signal names.
700 2.7 Changing Directories
702 By default, ksh maintains a logical view of the file system
703 hierarchy which makes symbolic links transparent. For
704 systems that have symbolic links, this means that if /bin is
705 a symbolic link to /usr/bin and you change directory to
706 /bin, pwd will indicate that you are in /bin, not /usr/bin.
707 pwd -P generates the physical pathname of the present
708 working directory by resolving all the symbolic links. By
709 default, the cd command will take you where you expect to go
710 even if you cross symbolic links. A subsequent cd .. in the
711 example above will place you in /, not /usr. On systems
712 with symbolic links, cd -P causes .. to be treated
716 BELL LABORATORIES PROPRIETARY
717 Not for use or disclosure outside Bell Laboratories except by
718 written approval of the director of the distributing organization.
734 ksh remembers your last directory in the variable OLDPWD.
735 The cd built-in can be given with argument - to return to
736 the previous directory and prints the name of the directory.
737 Note that cd - done twice returns you to the starting
738 directory, not the second previous directory. A directory
739 stack manager has been written as shell functions to push
740 and pop directories from the stack.
744 When ksh reads commands from a terminal, it issues a prompt
745 whenever it is ready to accept more input and then waits for
746 the user to respond. The TMOUT variable can be set to be
747 the number of seconds that the shell will wait for input
748 before terminating. A 60 second warning message is printed
751 The shell uses two prompts. The primary prompt, defined by
752 the value of the PS1 variable, is issued at the start of
753 each command. The secondary prompt defined by the value of
754 the PS2 variable, is issued when more input is needed to
757 ksh allows that user to specify a list of files or
758 directories to check before issuing the PS1 prompt. The
759 variable MAILPATH is a colon ( : ) separated list of file
760 names to be checked for changes periodically. The user is
761 notified before the next prompt. Each of the names in this
762 list can be followed by a ? and a prompt to be given when a
763 change has been detected in the file. The prompt will be
764 evaluated for parameter substitution. The parameter $_
765 within a mail message will evaluate to the name of the file
766 that has changed. The parameter MAILCHECK is used to
767 specify the minimal interval in seconds before new mail is
770 In addition to replacing each ! in the prompt with the
771 command version, ksh expands the value of the PS1 variable
772 for parameters expansions, arithmetic expansions, and
773 command substitutions as described below to generate the
774 prompt. The expansion characters that are to be applied
775 when the prompt is issued must be quoted to prevent the
776 expansions from occurring when assigning the value to PS1.
777 For example, PS1="$PWD" causes PS1 to be set to the value of
778 PWD at the time of the assignment whereas PS1='$PWD' causes
779 PWD to be expanded at the time the prompt is issued.
782 BELL LABORATORIES PROPRIETARY
783 Not for use or disclosure outside Bell Laboratories except by
784 written approval of the director of the distributing organization.
800 Command substitution may require a separate process to
801 execute and cause the prompt display to be somewhat slow,
802 especially when the return key is pressed several times in a
803 row. Therefore, its use within PS1 is discouraged. Some
804 variables are maintained by ksh so that their values can be
805 used with PS1. The PWD variable stores the pathname of the
806 current working directory. The value of SECONDS variable is
807 the value of the most recent assignment plus the elapsed
808 time. By default, the time is measured in milli-seconds,
809 but since SECONDS is a floating point variable, the number
810 of places after the decimal point in the expanded value can
811 be specified with typeset -Fplaces SECONDS. In a roundabout
812 way, this variable can be used to generate a time stamp into
813 the PS1 prompt without creating a process at each prompt.
814 The following code explains how you can do this on System V.
815 On BSD, you need another command to initialize the SECONDS
819 # . this script and use $TIME as part of your PS1 string to
820 # get the time of day in your prompt
821 typeset -RZ2 _x1 _x2 _x3
822 (( SECONDS=$(date '+3600*%H+60*%M+%S') ))
823 _s='_x1=(SECONDS/3600)%24,_x2=(SECONDS/60)%60,_x3=SECONDS%60,0'
824 TIME='"${_d[_s]}$_x1:$_x2:$_x3"'
825 # PS1=${TIME}whatever
829 2.9 Tilde substitution
831 The character ~ at the beginning of a word has special
832 meaning to ksh. If the characters after the ~ up to a /
833 match a user login name in the password database, then the ~
834 and the name are replaced by that user's login directory.
835 If no match is found, the original word is unchanged. A ~
836 by itself, or in front of a /, is replaced by the value of
837 the HOME parameter. A ~ followed by a + or - is replaced by
838 the value of $PWD and $OLDPWD respectively.
842 The output of built-in commands and traces have values
843 quoted so that they can be re-input to the shell. This
844 makes it easy to use cut and paste shell output on systems
845 which use a pointing device such as a mouse. In addition,
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849 Not for use or disclosure outside Bell Laboratories except by
850 written approval of the director of the distributing organization.
866 output can be saved in a file for reuse.
870 When an interactive ksh starts, it evaluates the $ENV
871 variable to arrive at a file name. If this value is not
872 null, ksh attempts to read and process commands in a file by
873 this name. Earlier versions of ksh read the ENV file for
874 all invocations of the shell primarily to allow function
875 definitions to be available for all shell invocations. The
876 function search path, FPATH, described later, eliminated the
877 primary need for this capability and it was removed because
878 the high performance cost was no longer deemed acceptable.
881 3. PROGRAMMING LANGUAGE
883 The KornShell vastly extends the set of applications that
884 can be implemented efficiently at the shell level. It does
885 this by providing simple yet powerful mechanisms to perform
886 arithmetic, pattern matching, substring generation, and
887 arrays. Users can write applications as separate functions
888 that can be defined in the same file or in a library of
889 functions stored in a directory and loaded on demand.
891 3.1 String Processing
893 The shell is primarily a string processing language. By
894 default, variables hold variable length strings. There are
895 no limits to the length of strings. Storage management is
896 handled by the shell automatically. Declarations are not
897 required. With most programming languages, string constants
898 are designated by enclosing characters in single quotes or
899 double quotes. Since most of the words in the language are
900 strings, the shell requires quotes only when a string
901 contains characters that are normally processed specially by
902 the shell, but their literal meaning is intended. However,
903 since the shell is a string processing language, and some
904 characters can occur as literals and as language
905 metacharacters, quoting is an important part of the
908 There are four quoting mechanisms in ksh. The simplest is
909 to enclose a sequence of characters inside single quotes.
910 All characters between a pair of single quotes have their
911 literal meaning; the single quote itself cannot appear. A $
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915 Not for use or disclosure outside Bell Laboratories except by
916 written approval of the director of the distributing organization.
932 immediately preceding a single quoted string causes all the
933 characters until the matching single quote to be interpreted
934 as an ANSI-C language string. Thus, '\n' represents
935 characters \ and n, whereas, $'\n' represents the new-line
936 character. Double quoted strings remove the special meaning
937 of all characters except $, and `, so that parameter
938 expansion and command substitution (defined below) are
939 performed. The final mechanism for quoting a character is
940 by preceding it with the escape character \. This mechanism
941 works outside of quoted strings and for the characters $, `,
942 ", and \ in double quoted strings.
944 Variables are designated by one or more strings of
945 alphanumeric characters beginning with an alphabetic
946 character separated by a .. Upper and lowercase characters
947 are distinct, so that the variable A and a are names of
948 different variables. There is no limit to the length of the
949 name of a variable. You do not have to declare variables.
950 You can assign a value to a variable by writing the name of
951 the variable, followed by an equal sign, followed by a
952 character string that represents its value. To create a
953 variable whose name contains a ., the variable whose name
954 consists of the characters before the last . must already
955 exist. You reference a variable by putting the name inside
956 curly braces and preceding the braces with a dollar sign.
957 The braces may be omitted when the name is alphanumeric. If
958 x and y are two shell variables, then to define a new
959 variable, z, whose value is the concatenation of the values
960 of x and y, you just say z=$x$y. It is that easy.
962 The $ can be thought of as meaning "value of." You can also
963 capture the output of any command with the notation
964 $(command). This is referred to as command substitution.
965 For example, x=$(date) assigns the output from the date
966 command to the variable x. Command substitution in the
967 Bourne shell is denoted by enclosing the command between
968 backquotes, (``). This notation suffers from some
969 complicated quoting rules. Thus, it is hard to write sed
970 patterns which contains back slashes within command
971 substitution. Putting the pattern in single quotes is of
972 little help. ksh accepts the Bourne shell command
973 substitution syntax for backward compatibility. The
974 $(command) notation allows the command itself to contain
975 quoted strings even if the substitution occurs within double
976 quotes. Nesting is legal.
980 BELL LABORATORIES PROPRIETARY
981 Not for use or disclosure outside Bell Laboratories except by
982 written approval of the director of the distributing organization.
998 The special command substitution of the form $(cat file) can
999 be replaced by $(< file), which is faster because the cat
1000 command doesn't have to run.
1002 3.2 Shell Parameters and Variables
1004 There are three types of parameters used by ksh, special
1005 parameters, positional parameters, and named parameters
1006 which are called variables. ksh defines the same special
1007 characters, 0, *, @, #, ?, $, !, and -, as they are defined
1008 in the Bourne shell.
1010 Positional parameters are set when the shell is invoked, as
1011 arguments to the set built-in, and by calls to functions
1012 (see below) and . procedures. They are named by a number
1015 The third type of parameter is a variable. As mentioned
1016 earlier, ksh uses variables whose names consist of one or
1017 more alpha-numeric strings separated by a .. There is no
1018 need to specify the type of a variable in the shell because,
1019 by default, variables store strings of arbitrary length and
1020 values will automatically be converted to numbers when used
1021 in an arithmetic context. However, ksh variables can have
1022 one or more attributes that control the internal
1023 representation of the variable, the way the variable is
1024 printed, and its access or scope. In addition, ksh allows
1025 variables to represent arrays of values and references to
1026 other variables. The typeset built-in command of ksh
1027 assigns attributes to variables. Two of the attributes,
1028 readonly and export, are available in the Bourne shell.
1029 Most of the remaining attributes are discussed here. The
1030 complete list of attributes appears in the manual. The
1031 unset built-in of ksh removes values and attributes of
1032 variables. When a variable is exported, certain of its
1033 attributes are also exported.
1035 Whenever a value is assigned to a variable, the value is
1036 transformed according to the attributes of the variable.
1037 Changing the attribute of a variable can change its value.
1038 The attributes -L and -R are for left and right field
1039 justification respectively. They are useful for aligning
1040 columns in a report. For each of these attributes, a width
1041 can be defined explicitly or else it is defined the first
1042 time an assignment is made to the variable. Each assignment
1043 causes justification of the field, truncating if necessary.
1046 BELL LABORATORIES PROPRIETARY
1047 Not for use or disclosure outside Bell Laboratories except by
1048 written approval of the director of the distributing organization.
1064 Assignment to fixed sized variables provides one way to
1065 generate a substring consisting of a fixed number of
1066 characters from the beginning or end of a string. Other
1067 methods are discussed later.
1069 The attributes -u and -l, are used for upper case and lower
1070 case formatting respectively. Since it makes no sense to
1071 have both attributes on simultaneously, turning on either of
1072 these attributes turns the other off. The following script,
1073 using read and print which are described later, provides an
1074 example of the use of shell variables with attributes. This
1075 script reads a file of lines each consisting of five fields
1076 separated by : and prints fields 4 and 2 in upper case in
1077 columns 1-15, left justified, and columns 20-25 right-
1078 justified respectively.
1080 typeset -uL15 f4 # 15 character left justified
1081 typeset -uR6 f2 # 6 character right justified
1082 IFS=: # set field separator to :
1083 while read -r f1 f2 f3 f4 f5 # read line, split into fields
1084 do print -r -- "$f4 $f2" # print fields 4 and 2
1088 The -i, -E, and -F, attributes are used to represent
1089 numbers. Each can be followed by a decimal number. The -i
1090 attribute causes the value to be represented as an integer
1091 and it can be followed by a number representing the numeric
1092 base when expanding its value. Whenever a value is assigned
1093 to an integer variable, it is evaluated as an arithmetic
1094 expression and then truncated to an integer.
1096 The -E attribute causes the value to be represented in
1097 scientific notation whenever its value is expanded. The
1098 number following the -E determines the number of significant
1099 figures, and defaults to 6. The -F attribute causes the
1100 value to be represented with a fixed number of places after
1101 the decimal point. Assignments to variables of the -E or -F
1102 cause the evaluation of the right hand side of the
1105 ksh allows one-dimensional arrays in addition to simple
1106 variables. There are two types of arrays; associative
1107 arrays and indexed arrays. The subscript for an associative
1108 array is an arbitrary string, whereas the subscript for an
1109 indexed array is an arithmetic expression that is evaluated
1112 BELL LABORATORIES PROPRIETARY
1113 Not for use or disclosure outside Bell Laboratories except by
1114 written approval of the director of the distributing organization.
1130 to yield an integer index. Any variable can become an
1131 indexed array by referring to it with a subscript. All
1132 elements of an array need not exist. Subscripts for arrays
1133 must evaluate to an integer between 0 and some maximum
1134 value, otherwise an error results. The maximum value may
1135 vary from one machine to another but is at least 4095.
1136 Evaluation of subscripts is described in the next section.
1137 Attributes apply to the whole array.
1139 Assignments to array variables can be made to individual
1140 elements via parameter assignment commands or the typeset
1141 built-in. Additionally, values can be assigned sequentially
1142 using the -A name option of the set command. Referencing of
1143 subscripted variables requires the character $, but also
1144 requires braces around the array element name. The braces
1145 are needed to avoid conflicts with the file name generation
1146 mechanism. The form of any array element reference is:
1148 A subscript value of * or @ can be used to generate all
1149 elements of an array, as they are used for expansion of
1150 positional parameters. The list of currently defined
1151 subscripts for a given variable can be generated with
1152 ${!name[@]}, or ${!name[*]}.
1154 The nameref attribute causes the variable to be treated as a
1155 reference to the variable defined by its value. Once this
1156 attribute is set, all references to this variable become
1157 references to the variable named by the value of this
1158 variable. For example, if foo=bar, then setting the
1159 reference attribute on foo will call all subsequent
1160 references to foo to behave as references to bar. Unsetting
1161 this attribute breaks the association. Reference variables
1162 are usually used inside functions whose arguments are the
1163 name of a shell variable. The names for reference variables
1164 cannot contain a .. Whenever a shell variable is
1165 referenced, the portion of the variable up to the first .
1166 is checked to see whether it matches the name of a reference
1167 variable. If it does, then the name of the variable
1168 actually used consists of the concatenation of the name of
1169 the variable defined by the reference plus the remaining
1170 portion of the original variable name. For example, using
1171 the predefined alias, alias nameref='typeset -n',
1173 .bar.home.bam="hello world"
1174 nameref foo=.bar.home
1178 BELL LABORATORIES PROPRIETARY
1179 Not for use or disclosure outside Bell Laboratories except by
1180 written approval of the director of the distributing organization.
1199 3.3 Substring Generation
1201 The expansion of a variable or parameter can be modified so
1202 that only a portion of the value results. It is often
1203 necessary to extract a portion of a shell variable or a
1204 portion of an array. There are several parameter expansion
1205 operators that can do this. One method to generate a
1206 substring is with an expansion of the form
1207 ${name:offset:length} where offset is an arithmetic
1208 expression that defines the offset of the first character
1209 starting from 0, and length is an arithmetic expression that
1210 defines the length of the substring. If :length is omitted,
1211 the length of the value of name starting at offset is used.
1212 The :offset:length operators can also be applied to array
1213 expansions and to parameters * and @ to generate portions of
1214 an array. For example, the expansion,
1215 ${name[@]:offset:length}, yields up to length elements of
1216 the array name starting at the element offset.
1218 The other parameter expansion modifiers use shell patterns
1219 to describe portions of the string to modify and delete. A
1220 description of shell patterns is contained below. When
1221 these modifiers are applied to special parameters @ and * or
1222 to array parameters given as name[@] or name[*], the
1223 operation is performed on each element. There are four
1224 parameter substitution modifiers that strip off leading and
1225 trailing substrings during parameter substitution by
1226 removing the characters matching a given pattern. An
1227 expansion of the form ${name#pattern} causes the smallest
1228 matching prefix of the value of name to be removed. The
1229 largest prefix matching pattern is removed by using ##
1230 instead of #. Similarly, an expansion of the form
1231 ${name%pattern} causes the smallest matching substring at
1232 the end of name to be removed. Again, using %% instead of
1233 %, causes the largest matching trailing substring to be
1234 deleted. For example, if the shell variable file has value
1235 foo.c, then the expression ${file%.c}.o has value foo.o.
1237 The value of an expansion can be changed by specifying a
1238 pattern that matches the part that needs to be changed after
1239 the the parameter expansion modifier /. An expansion of the
1240 form ${name/pattern/string} replaces the first match of
1241 pattern with the value of variable name to string. The
1244 BELL LABORATORIES PROPRIETARY
1245 Not for use or disclosure outside Bell Laboratories except by
1246 written approval of the director of the distributing organization.
1262 second / is not necessary when string is null. The
1263 expansion ${name//pattern/string} changes all occurrences of
1264 the pattern into string. The parameter expansion modifiers
1265 /# and /% cause the matching pattern to be anchored to the
1266 beginning and end respectively.
1268 Finally, there are parameter expansion modifiers that yield,
1269 the name of the variable, the string length of the value or
1270 the number of elements of an array. ${!name} yields the
1271 name of the variable which will be name itself except when
1272 name is a reference variable. In this case it will yield
1273 the name of the variable it refers to. ${#name} will be the
1274 length in bytes of $name. For an array variable ${#name[*]}
1275 gives the number of elements in the array.
1277 3.4 Arithmetic Evaluation
1279 For the most part, the shell is a string processing
1280 language. However, the need for arithmetic has long been
1281 obvious. Many of the characters that are special to the
1282 Bourne shell, are needed as arithmetic operators. To make
1283 arithmetic easy to use, and to maintain compatibility with
1284 the Bourne shell, ksh uses matching (( and )) to delineate
1285 arithmetic expressions. While single parentheses might have
1286 been more desirable, these already mean subshell so that
1287 another notation was required. The arithmetic expression
1288 inside the double parentheses follows that same syntax,
1289 associativity and precedence as the ANSI-C[15] programming
1290 language. The characters between the matching double
1291 parentheses are processed with the same rules used for
1292 double quotes so that spaces can be used to aid readability
1293 without additional quoting.
1295 All arithmetic evaluations are performed using double
1296 precision floating point arithmetic. Floating point
1297 constants follow the same rules as the ANSI-C programming
1298 language. Integer arithmetic constants are written as
1300 where base is a decimal integer between two and sixty-four
1301 and number is any non-negative number. Base ten is used
1302 when no base is specified. The digits are represented by
1303 the characters 0-9a-zA-Z_@. For bases less than or equal to
1304 36, upper and lower case characters can be used
1305 interchangibly to represent the digits from 10 thru 35.
1310 BELL LABORATORIES PROPRIETARY
1311 Not for use or disclosure outside Bell Laboratories except by
1312 written approval of the director of the distributing organization.
1328 Arithmetic expressions are made from constants, variables,
1329 operators. Parentheses may be used for grouping. The
1330 contents inside the double parentheses are processed with
1331 the same expansions as occurs in a double quoted string, so
1332 that all $ expansions are performed before the expression
1333 are performed. However, there is no need to use the $ to
1334 get the value of a variable because the arithmetic evaluator
1335 replaces the name of the variable by its value within an
1336 arithmetic expression. The $ cannot be used when the
1337 variable is the subject of assignment or an increment
1338 operation. As a rule it is better not to use $ in front of
1339 variables in an arithmetic expression.
1341 An arithmetic command of the form (( ... )) is a command
1342 that evaluates the enclosed arithmetic expression. For
1343 example, the command
1345 can be used to increment the variable x, assuming that x
1346 contains some numerical value. The arithmetic command is
1347 true (return value 0), when the resulting expression is
1348 non-zero, and false (return value 1) when the expression
1349 evaluates to zero. This makes the command easy to use with
1350 the if and while compound command.
1352 The for compound command has been extended for use in
1353 arithmetic contexts. The syntax,
1354 for (( expr1; expr2 ; expr3 ))
1355 can be used as the first line of a for loop with the same
1356 semantics as the for statement in the ANSI-C programming
1359 Arithmetic evaluations can also be performed as part of the
1360 evaluation of a command line. The syntax $(( ... )) expands
1361 to the value of the enclosed arithmetic expression. This
1362 expansion can occur wherever parameter expansion is
1363 performed. For example using the ksh command print
1366 prints the number 4.
1368 The following script prints the first n lines of its
1369 standard input onto its standard output, where n can be
1370 supplied as an optional argument whose default value is 20.
1372 integer n=${1-20} # set n
1373 while (( n-- >=0 )) && read -r line # at most n lines
1376 BELL LABORATORIES PROPRIETARY
1377 Not for use or disclosure outside Bell Laboratories except by
1378 written approval of the director of the distributing organization.
1394 do print -r -- "$line"
1398 3.5 Shell Expansions
1400 The commands you enter from the terminal or from a script
1401 are divided into words and each word undergoes several
1402 expansions to generate the command name and its arguments.
1403 This is done in two phases. The first phase recognizes
1404 reserved words, spaces and operators to decide where command
1405 boundaries lie. Alias substitutions take place during this
1406 phase. The second phase performs expansions in the
1409 + Tilde substitution, parameter expansion, arithmetic
1410 expansion, and command substitution are performed from
1413 + The characters that result from parameter expansion and
1414 command substitution above are checked with the
1415 characters in the IFS variable for possible field
1416 splitting. (See a description of read below to see how
1417 IFS is used.) Setting IFS to a null value causes field
1418 splitting to be skipped.
1420 + Pathname generation (as described below) is performed
1421 on each of the fields. Any field that doesn't match a
1422 pathname is left alone. The option, -f or noglob, is
1423 used to disable pathname generation.
1425 3.6 Pattern Matching
1427 The shell is primarily a string processing language and uses
1428 patterns for matching file names as well as for matching
1429 strings. The characters ?, *, and [ are processed specially
1430 by the shell when not quoted. These characters are used to
1431 form patterns that match strings. Patterns are used by the
1432 shell to match pathnames, to specify substrings, and for
1433 case commands. The character ? matches any one character.
1434 The character * matches zero or more characters. The
1435 character sequence [...] defines a character class that
1436 matches any character contained within []. A range of
1437 characters can be specified by putting a - between the first
1438 and last character of the range. An exclamation mark, !,
1439 immediately after the [, means match all characters except
1442 BELL LABORATORIES PROPRIETARY
1443 Not for use or disclosure outside Bell Laboratories except by
1444 written approval of the director of the distributing organization.
1460 the characters specified. For example, the pattern
1461 a?c*.[!a-z] matches any string beginning with an a, whose
1462 third character is a c, and that ends in . (dot) followed
1463 by any character except the lowercase letters, a-z. The
1464 sequence [:alpha:] inside a character class, matches any set
1465 of characters in the ANSI-C alpha class. Similarly,
1466 [:class:] matches each of the characters in the given class
1467 for all the ANSI-C character classes.
1469 ksh treats strings of the form (pattern-list) , where
1470 pattern-list is a list of one or more patterns separated by
1471 a |, specially when preceded by *, ?, +, @, or !. A ?
1472 preceding (pattern-list) means that the pattern list
1473 enclosed in () is optional. An @(pattern-list) matches any
1474 pattern in the list of patterns enclosed in (). A
1475 *(pattern-list) matches any string that contains zero or
1476 more of each of the enclosed patterns, whereas +(pattern-
1477 list) requires a match of one or more of any of the given
1478 patterns. For instance, the pattern +([0-9])?(.) matches
1479 one or more digits optionally followed by a .(dot). A
1480 !(pattern-list) matches anything except any of the given
1481 patterns. For example, print !(*.o) will display any file
1482 name that does not end in .o.
1484 When patterns are used to generate pathnames when expanding
1485 commands several other rules apply. A separate match is
1486 made for each matching on each file name component of the
1487 pathname. Read permission is required for any portion of the
1488 pathname that contains any special pattern character. Search
1489 permission is required for every component except possibly
1492 By default, file names in each directory that begin with .
1493 are skipped when performing a match. If the pattern to be
1494 matched starts with a leading ., then only files beginning
1495 with a ., are considered when finding matching files. If
1496 the FIGNORE variable is set, then only files that do not
1497 match this pattern are considered. This overrides the
1498 special meaning of . in a pattern and in a file name.
1500 If the markdirs option is set, each matching pathname that
1501 is the name of a directory has a trailing / appended to the
1508 BELL LABORATORIES PROPRIETARY
1509 Not for use or disclosure outside Bell Laboratories except by
1510 written approval of the director of the distributing organization.
1526 3.7 Conditional Expressions
1528 The Bourne shell uses the test command, or the equivalent [
1529 command, to test the attributes for files and to compare
1530 strings or numbers. The problem with test is that the shell
1531 has expanded the words of the test command and split them
1532 into arguments before test begins execution. test cannot
1533 distinguish between operators and operands. In most cases
1534 test "$1" will test whether argument 1 is non-null.
1535 However, if argument 1 is -f, then test will treat -f as an
1536 operator and yield a syntax error. One of the most frequent
1537 errors with test occurs when its operands are not within
1538 double quotes. In this case, the argument may expand to
1539 more than a single argument or to no argument at all. In
1540 either case this will likely cause a syntax error. What
1541 makes this most insidious is that these errors are
1542 frequently data dependent. A script that appears to run
1543 correctly may abort if given unexpected data.
1545 To get around these problems, ksh has a compound command for
1546 condition expression testing as part of the language. The
1547 reserved words [[ and ]] delimit the range of the command.
1548 Because they are reserved words, not operator characters,
1549 they require spaces to separate them from arguments. The
1550 words between [[ and ]] are not processed for field
1551 splitting or for pathname generation. In addition, since
1552 ksh determines the operators before parameter expansion,
1553 expansions that yield no argument cause no problem. The
1554 operators within [[...]] are almost the same as those for
1555 the test command. All unary operators are of the form
1556 -letter and are followed by a single operand. Instead of -a
1557 and -o, [[...]] uses && and || to indicate "and" and "or".
1558 Parentheses are used without quoting for grouping.
1560 The right hand side of the string comparison operators ==
1561 and != take a pattern and tests whether the left hand
1562 operand matches this pattern. Quoting the pattern results
1563 is a string comparison rather than the pattern match. The
1564 operators < and > within [[...]] designate lexicographical
1567 In addition there are several other new comparison
1568 primitives. The binary operators -ot and -nt compare the
1569 modification times of two files to see which file is older
1570 than or newer than the other. The binary operator -ef tests
1571 whether two files have the same device and i-node number,
1574 BELL LABORATORIES PROPRIETARY
1575 Not for use or disclosure outside Bell Laboratories except by
1576 written approval of the director of the distributing organization.
1592 i. e., a link to the same file.
1594 The unary operator -L returns true if its operand is a
1595 symbolic link. The unary operator -O ( -G ) returns true if
1596 the owner (or group) of the file operand matches that of the
1597 caller. The unary operator -o returns true when its operand
1598 is the name of an option that is currently on.
1600 The following script illustrates some of the uses of
1601 [[...]]. The reference manual contains the complete list of
1605 do # execute foo for numeric directory
1606 if [[ -d $i && $i == +([0-9]) ]]
1608 # otherwise if writable or executable file and not mine
1609 elif [[ (-w $i||-x $i) && ! -O $i ]]
1615 3.8 Input and Output
1617 ksh has extended I/O capabilities to enhance the use of the
1618 shell as a programming language. As with the Bourne shell,
1619 you use the I/O redirection operator, <, to control where
1620 input comes from, and the I/O redirection operator, >, to
1621 control where output goes to. Each of these operators can be
1622 preceded with a single digit that specifies a file unit
1623 number to associate with the file stream. Ordinarily you
1624 specify these I/O redirection operators with a specific
1625 command to which it applies. However, if you specify I/O
1626 redirections with the exec command, and don't specify
1627 arguments to exec, then the I/O redirection applies to the
1628 current program. For example, the command exec < foobar
1629 opens file foobar for reading. The exec command is also
1630 used to close files. A file descriptor unit can be opened
1631 as a copy of an existing file descriptor unit by using
1632 either of the <& or >& operators and putting the file
1633 descriptor unit of the original file after the &. Thus,
1634 2>&1 means open standard error (file descriptor 2) as a copy
1635 of standard output (file descriptor 1). A file descriptor
1636 value of - after the & indicates that the file should be
1637 closed. To close file unit 5, specify exec 5<&-. There are
1640 BELL LABORATORIES PROPRIETARY
1641 Not for use or disclosure outside Bell Laboratories except by
1642 written approval of the director of the distributing organization.
1658 two additional redirection operators with ksh and the POSIX
1659 shell that are not part of the Bourne shell. The >|
1660 operator overrides the effect of the noclobber option
1661 described earlier. The <> operator causes a file to be
1662 opened for both reading and writing.
1664 ksh recognizes certain pathnames and treats them specially.
1665 Pathnames of the form /dev/fd/n are treated as equivalent to
1666 the file defined by file descriptor n. These name can be
1667 used as the script argument to ksh and in conditional
1668 testing as described above. On underlying systems that
1669 support /dev/fd in the file system, these names can be
1670 passed to other commands. Pathnames of the form
1671 /dev/tcp/hostid/port and /dev/udp/hostid/port can be used to
1672 create tcp and udp connections to services given by the
1673 hostid number and port number. The hostid cannot use
1674 symbolic values. In practice these are typically generated
1675 by command substitution. For example,
1676 exec 5> /dev/tcp/$(service name) would open file descriptor
1677 5 for sending messages to hostid and port number defined by
1678 the output of service name.
1680 The Bourne shell has a built-in command read for reading
1681 lines from standard input (file descriptor 0) and splitting
1682 it into fields based on the value of the IFS variable, and a
1683 command echo to write strings to standard output. ( On some
1684 systems, echo is not a built-in command and incurs
1685 considerable overhead to use.) Unfortunately, neither of
1686 these commands is able to perform some very basic tasks.
1687 For example. with the Bourne shell, the read built-in
1688 cannot read a single line that end in \. With ksh the read
1689 built-in has a -r option to remove the special meaning for \
1690 which allows it to be treated as a regular character rather
1691 than the line continuation character. With the Bourne
1692 shell, there is no simple way to have more than one file
1693 open at any time for reading. ksh has options on the read
1694 command to specify the file descriptor for the input. The
1695 fields that are read from a line can be stored into an
1696 indexed array with the -A option to read. This allows a
1697 line to be split into an arbitrary number of fields.
1699 The way the Bourne shell uses the IFS variable to split
1700 lines into fields greatly limits its utility. Often data
1701 files consist of lines that use a character such as : to
1702 delimit fields with two adjacent delimiters that denote a
1703 null field. The Bourne shell treats adjacent delimiters as
1706 BELL LABORATORIES PROPRIETARY
1707 Not for use or disclosure outside Bell Laboratories except by
1708 written approval of the director of the distributing organization.
1724 a single field delimiter. With ksh, delimiters that are
1725 considered white space characters have the behavior of the
1726 Bourne shell, but other adjacent delimiters separate null
1729 The read command is often used in scripts that interact with
1730 the user by prompting the user and then requesting some
1731 input. With the Bourne shell two commands are needed; one
1732 to prompt the user, the other to read the reply. ksh allows
1733 these two commands to be combined. The first argument of
1734 the read command can be followed by a ? and a prompt string
1735 which is used whenever the input device is a terminal.
1736 Because the prompt is associated with the read built-in, the
1737 built-in command line editors will be able to re-output the
1738 prompt whenever the line needs to be refreshed when reading
1739 from a terminal device.
1741 With the Bourne shell, there is no way to set a time limit
1742 for waiting for the user response to read. The -t option to
1743 read takes a floating point argument that gives the time in
1744 seconds, or fractions of seconds that the shell should wait
1747 The version of the echo command in System V treats certain
1748 sequences beginning with \ as control sequences. This makes
1749 it hard to output strings without interpretation. Most BSD
1750 derived systems do not interpret \ control sequences.
1751 Unfortunately, the BSD versions of echo accepts a -n option
1752 to prevent a trailing new-line, but has no way to cause the
1753 string -n to be printed. Neither of these versions is
1754 adequate. Also, because they are incompatible, it is very
1755 hard to write portable shell scripts using echo. The ksh
1756 built-in, print, outputs characters to the terminal or to a
1757 file and subsumes the functions of all versions of echo.
1758 Ordinarily, escape sequences in arguments beginning with \
1759 are processed the same as for the System V echo command.
1760 However print follows the standard conventions for options
1761 and has options that make print very versatile. The -r
1762 option can be used to output the arguments without any
1763 special meaning. The -n option can be used here to suppress
1764 the trailing new-line that is ordinarily appended. As with
1765 read, it is possible to specify the file descriptor number
1766 as an option to the command to avoid having to use
1767 redirection operators with each occurrence of the command.
1772 BELL LABORATORIES PROPRIETARY
1773 Not for use or disclosure outside Bell Laboratories except by
1774 written approval of the director of the distributing organization.
1790 The IEEE POSIX shell and utilities standard committee was
1791 unable to reconcile the differences between the System V and
1792 BSD versions of echo. They introduced a new command named
1793 printf which takes an ANSI-C format string and a list of
1794 options and outputs the strings using the ANSI-C formatting
1795 rules. Since ksh is POSIX conforming, it accepts printf.
1796 However, there is a -f options to print that can be used to
1797 specify a format string which processes the arguments the
1798 same way that printf does.
1800 The format processing for print and printf has been extended
1801 slightly. There are three additional formatting directives.
1802 The %b format causes the \ escape sequences to be expanded
1803 as they are with the System V echo command. The %q format
1804 causes quotes to be placed on the output as required so that
1805 it can be used as shell input. Special characters in the
1806 output of most ksh built-in commands and in the output from
1807 an execution trace are quoted in an equivalent fashion. The
1808 %P format causes an extended regular expression string to be
1809 converted into a shell pattern. This is useful for writing
1810 shell applications that have to accept regular expression as
1811 input. Finally, the escape sequence \E which expands to the
1812 terminal escape character (octal 033) has been added.
1814 The shell is frequently used as a programming language for
1815 interactive dialogues. The select statement has been added
1816 to the language to make it easier to present menu selection
1817 alternatives to the user and evaluate the reply. The list
1818 of alternatives is numbered and put in columns. A user
1819 settable prompt, PS3, is issued and if the answer is a
1820 number corresponding to one of the alternatives, the select
1821 loop variable is set to this value. In any case, the REPLY
1822 variable is used to store the user entered reply. The shell
1823 variables LINES and COLUMNS are used to control the layout
1828 ksh can spawn a co-process by adding a |& after a command.
1829 This process will be run with its standard input and its
1830 standard output connected to the shell. The built-in
1831 command print with the -p option will write into the
1832 standard input of this process and the built-in command read
1833 with the -p option will read from the output of this
1838 BELL LABORATORIES PROPRIETARY
1839 Not for use or disclosure outside Bell Laboratories except by
1840 written approval of the director of the distributing organization.
1856 In addition, the I/O redirection operators <& and >& can be
1857 used to move the input or output pipe of the co-process to a
1858 numbered file descriptor. Use exec 3>& p to move the input
1859 of the co-process to file descriptor 3. After you have
1860 connected to file descriptor 3, you can direct the output of
1861 any command to the co-process by running command >&3. Also,
1862 by moving the input of the co-process to a numbered
1863 descriptor, it is possible to run a second co-process. The
1864 output of both co-processes will be the file descriptor
1865 associated with read -p. You can use exec 4< p to cause the
1866 output of these co-processes to go to file descriptor 4 of
1867 the shell. Once you have moved the pipe to descriptor 4, it
1868 is possible to connect a server to the co-process by running
1869 command 4<& p or to close the co-process pipe with
1874 Function definitions are of the form
1881 A function whose name contains a . is called a discipline
1882 function. The portion of the name before the last . must
1883 refer to the name of an existing variable. Thus, if p is a
1884 reference to PATH, then the function name p.get and PATH.get
1885 refer to the same function.
1887 The function is invoked either by specifying name as the
1888 command name and optionally following it with arguments or
1889 by using it as an option to the . built-in command.
1890 Positional parameters are saved before each function call
1891 and restored when completed. The arguments that follow the
1892 function name on the calling line become positional
1893 parameters inside the function. The return built-in can be
1894 used to cause the function to return to the statement
1895 following the point of invocation.
1897 Functions can also be defined with the System V notation,
1904 BELL LABORATORIES PROPRIETARY
1905 Not for use or disclosure outside Bell Laboratories except by
1906 written approval of the director of the distributing organization.
1924 Functions defined with this syntax cannot be used as the
1925 first argument to a . procedure. ksh accepts this notation
1926 for compatibility only. There is no need to use this
1927 notation when writing ksh scripts.
1929 Functions defined with the function name syntax and invoked
1930 by name are executed in the current shell environment and
1931 can share named variables with the calling program.
1932 Options, other than execution trace -x, set by the calling
1933 program are passed down to a function. The options are not
1934 shared with the function so that any options set within a
1935 function are restored when the function exits. Traps
1936 ignored by the caller are ignored within the function and
1937 cannot be enabled. Traps caught by the calling program are
1938 reset to their default action with the function. In most
1939 instances, the default action is to cause the function to
1940 terminate. A trap on EXIT, defined within a function
1941 executes after the function completes but before the caller
1942 resumes. Therefore, any variable assignments and any
1943 options set as part of a trap action will be effective after
1946 By default, variables are inherited by the function and
1947 shared by the calling program. However, for functions
1948 defined with the function name syntax that are invoked by
1949 name, environment substitutions preceding the function call
1950 apply only to the scope of the function call. Also,
1951 variables whose names do not contain a . that are defined
1952 with the typeset built-in command are local to the function
1953 that they are declared in. Thus, for the function defined
1962 invoked as y=13 name, x and y are local variables with
1963 respect to the function name while z is global.
1965 Functions defined with the name() syntax, and functions
1966 invoked as an argument to the . command, share everything
1967 other than positional parameters with the caller.
1970 BELL LABORATORIES PROPRIETARY
1971 Not for use or disclosure outside Bell Laboratories except by
1972 written approval of the director of the distributing organization.
1988 Assignments that precede the call remain in effect after the
1991 Alias and function names are not passed down to shell
1992 scripts or carried across separate invocations of ksh. The
1993 $FPATH variable gives a colon separated list of directories
1994 that is searched for function definitions when trying to
1995 resolve the command name. Whenever a file name contained in
1996 $FPATH is found, the complete file is read and all functions
1997 contained within become defined.
1999 Calls that reference functions can be recursive. Except for
2000 special built-ins, function names take precedence over
2001 built-in names and names of programs when used as command
2002 names. To write a function to replace a built-in command or
2003 to replace a program, you must use the command built-in
2004 command. The arguments to command are the name and
2005 arguments of the program you want to execute. For example
2006 to write a cd function which changes the directory and
2007 prints out the directory name, you can write,
2012 then print -r -- $PWD
2017 The FPATH variable is a colon separated list that ksh uses
2018 to search for function definitions. When ksh encounters an
2019 autoload function, it runs the . command on the script
2020 containing the function, and then executes the function.
2022 Function definitions may also be placed in the ENV file.
2023 However, this causes the shell to take longer to begin
2026 3.11 Process Substitution
2028 This feature is only available on versions of the UNIX
2029 operating system which support the /dev/fd directory for
2030 naming open files. Each command argument of the form
2031 <(list) or >(list) will run process list asynchronously
2032 connected to some file in the /dev/fd directory. The name
2033 of this file will become the argument to the command. If
2036 BELL LABORATORIES PROPRIETARY
2037 Not for use or disclosure outside Bell Laboratories except by
2038 written approval of the director of the distributing organization.
2054 the form with > is selected then writing on this file will
2055 provide input for list. If < is used, then the file passed
2056 as an argument will contain the output of the list process.
2059 paste <(cut -f1 file1) <(cut -fB file2) | tee >(process1) >(process2)
2061 extracts fields 1 and 3 from the files file1 and file2
2062 respectively, places the results side by side, and sends it
2063 to the processes process1 and process2, as well as putting
2064 it onto the standard output. Note that the file which is
2065 passed as an argument to the command is a UNIX system
2066 pipe(2) so that the programs that expect to lseek(2) on the
2069 3.12 Finding Commands
2071 The addition of aliases, functions, and more built-ins has
2072 made it substantially more difficult to know what a given
2073 command word really means.
2075 There are several reasons that commands are built into the
2076 shell rather than being separate programs. Commands that
2077 begin with reserved words are an integral part of the shell
2078 language itself and typically define the control flow of the
2079 language. Some control flow commands are not reserved words
2080 in the language but are special built-ins. Special built-
2081 ins are built-ins that are considered a part of the language
2082 rather than user definable commands. The best examples of
2083 commands that fit this description are break and continue.
2084 Because they are not reserved words, they can be the result
2085 of shell expansions and are not effected by quoting. These
2086 commands have the following special properties:
2088 + Assignments that precede them apply to the current
2089 shell process, not just to the given command.
2091 + An error in the format of these commands cause a shell
2092 script or function that contains them to abort.
2094 + They cannot be overridden by shell functions.
2096 Other commands are built-in because they perform side
2097 effects on the current environment that would be nearly
2098 impossible to implement otherwise. Built-ins such as cd and
2099 read are examples of such built-ins. These built-ins are
2102 BELL LABORATORIES PROPRIETARY
2103 Not for use or disclosure outside Bell Laboratories except by
2104 written approval of the director of the distributing organization.
2120 semantically equivalent to commands that are not built-in
2121 except that they don't take a path search to locate.
2123 A third reason to have a command built-in is so that it will
2124 be unaffected by the setting of the PATH variable. The
2125 print command fits this category. Scripts that use print
2126 will be portable to all sites that run ksh.
2128 The final reason for having a command be a built-in is for
2129 performance. On most systems it is more than an order of
2130 magnitude faster to initiate a command that is built-in than
2131 to create a separate process to run the command. Example
2132 that fit this category are test and basename.
2134 Given a command name ksh decides what it means using the
2137 + Reserved words define commands that form part of the
2138 shell grammar. They cannot be quoted.
2140 + Alias substitutions occur first as part of the reading
2141 of commands. Using quotes in the command name will
2142 prevent alias substitutions.
2144 + Special built-ins come next.
2148 + Commands that are built-in that are not associated with
2151 + If the command name contains a /, the program or script
2152 corresponding to the given name is executed.
2154 + A path search locates the pathname corresponding to the
2155 command. If the pathname where it is found matches the
2156 pathname associated with a built-in command, the
2157 built-in command is executed. If the directory where
2158 the command is found is listed in the FPATH variable,
2159 the file is read into the shell like a dot script, and
2160 a function by that name is invoked. Once a pathname is
2161 found, ksh remembers its location and only checks
2162 relative directories in PATH the next time the command
2163 name is used. Assigning a value to PATH causes ksh to
2164 forget the location of all command names.
2168 BELL LABORATORIES PROPRIETARY
2169 Not for use or disclosure outside Bell Laboratories except by
2170 written approval of the director of the distributing organization.
2186 + The FPATH variable is searched and files found are
2187 treated as described above.
2189 The first argument of the command built-in, described
2190 earlier, skips the checks for reserved words and for
2191 function definitions. In all other ways, command behaves
2192 like a built-in that is not associated with a pathname. As
2193 a result, if the first argument of command is a special
2194 built-in, the special properties of this built-in do not
2195 apply. For example, whereas, exec 3< foo will cause a script
2196 containing it to abort if the open fails,
2197 command exec 3< foo results in a non-zero exit status but
2198 does not abort the script.
2200 You can get a complete list of the special built-in commands
2201 with builtin -s. In addition builtin without arguments gives
2202 a list of the current built-ins and the pathname that they
2203 are associated with. A built-in can be bound to another
2204 pathname by giving the pathname for the built-in. The
2205 basename of this path must be the name of an existing
2206 built-in for this to succeed. Specifying the name of the
2207 built-in without a pathname causes this built-in to be found
2208 before a path search. On systems with run time loading of
2209 libraries, built-in commands can be added with the builtin
2210 command. Each command that is to be built-in must be
2211 written as a C function whose name is of the form b_name,
2212 where name is the name of the built-in that is to be added.
2213 The function has the same argument calling convention as
2214 main. The lower eight bits of the return value become the
2215 exit status for this built-in. Builtins are added by
2216 specifying the pathname of the library as an argument to the
2217 -f option of builtin.
2219 A built-in command, whence, when used with the -v option has
2220 been provided to answer this question. A line is printed
2221 for each argument to whence telling what would happen if
2222 this argument were used as a command name. It reports on
2223 reserved words, aliases, built-ins, and functions. If the
2224 command is none of the above, it follows the path search
2225 rules and prints the full path-name, if any, otherwise it
2226 prints an error message.
2234 BELL LABORATORIES PROPRIETARY
2235 Not for use or disclosure outside Bell Laboratories except by
2236 written approval of the director of the distributing organization.
2254 To avoid implementation dependencies, ksh accepts and
2255 generates symbolic names for built-ins that use numerical
2256 values in the Bourne shell. The -S option of the umask
2257 built-in command accepts and displays default file creation
2258 permissions symbolically. It uses the same symbolic
2259 notation as the chmod command.
2261 The trap and kill built-in commands allows the signal names
2262 to be given symbolically. The names of signals and traps
2263 corresponding to signals are the same as the signal name
2264 with the SIG prefix removed. The trap 0 is named EXIT.
2268 A new trap named ERR has been added. This trap is invoked
2269 whenever the shell would exit if the -e option were set.
2270 This trap is used by Fourth Generation Make[16] which runs
2271 ksh as a co-process.
2273 A trap named DEBUG gets executed after each command. This
2274 trap can be used for debugging purposes. The KEYBD trap was
2279 The primary method for debugging Bourne shell scripts is to
2280 use the -x option to enable the execution trace. After all
2281 the expansions have been performed, but before each command
2282 is executed, the trace writes to standard error the name and
2283 arguments of each command preceded by a +. With ksh the PS4
2284 variable is evaluated for parameter substitution and is
2285 displayed before each command, instead of the +.
2287 The LINENO variable is set to the current line number
2288 relative to the beginning of the current script or function.
2289 It is most useful as part of the PS4 prompt.
2291 The variable RANDOM produces a random number in the range 0
2292 to 32767 each time it is referenced. Assignment to this
2293 variable sets the seed for the random number generator.
2295 The parameter PPID is used to generate the process id of
2296 the process which invoked this shell.
2300 BELL LABORATORIES PROPRIETARY
2301 Not for use or disclosure outside Bell Laboratories except by
2302 written approval of the director of the distributing organization.
2318 3.16 Timing Commands
2320 A reserved word time has been added to replace the time
2321 command. Any function, command or pipeline can be preceded
2322 by this reserved word to obtain information about the
2323 elapsed, user, and system times. Since I/O redirections
2324 bind to the command, not to time, parentheses should be used
2325 to redirect the timing information which is normally printed
2326 on file descriptor 2.
2331 There are several documented problems associated with the
2332 security of shell procedures[17]. These security holes
2333 occur primarily because a user can manipulate the
2334 environment to subvert the intent of a setuid shell
2335 procedure. Frequently, shell procedures are initiated from
2336 binary programs, without the author's awareness, by library
2337 routines which invoke shells to carry out their tasks. When
2338 the binary program is run setuid then the shell procedure
2339 runs with the permissions afforded to the owner of the
2342 In the Bourne shell, the IFS parameter is used to split each
2343 word into separate command arguments. If a user knows that
2344 some setuid program will run sh -c /bin/pwd (or any other
2345 command in /bin) then the user sets and exports IFS=/.
2346 Instead of running /bin/pwd the shell will run bin with pwd
2347 as an argument. The user puts his or her own bin program
2348 into the current directory. This program can create a copy
2349 of the shell, make this shell setuid, and then run the
2350 /bin/pwd program so that the original program continues to
2351 run successfully. This kind of penetration is not possible
2352 with ksh since the IFS parameter only splits arguments that
2353 result from command or parameter substitution.
2355 Some setuid programs run programs using system() without
2356 giving the full pathname. If the user sets the PATH
2357 variable so that the desired command will be found in his or
2358 her local bin, then the same technique described above can
2359 be employed to compromise the security of the system. To
2360 close up this and other security holes, ksh resets the
2361 effective user id to the real user id and the effective
2362 group id to the real group id unless the privileged option
2363 (-p) is specified at invocation. In this mode, the
2366 BELL LABORATORIES PROPRIETARY
2367 Not for use or disclosure outside Bell Laboratories except by
2368 written approval of the director of the distributing organization.
2384 privileged mode, the .profile and ENV files are not
2385 processed. Instead, the file /etc/suid_profile is read and
2386 executed. This gives an administrator control over the
2387 environment to set the PATH variable or to log setuid shell
2388 invocations. Clearly security of the system is compromised
2389 if /etc or this file is publicly writable.
2391 In the Berkeley UNIX version the operating system looks for
2392 the characters #! as the first two characters of an
2393 executable file. If these characters are found, then the
2394 next word on this line is taken as the interpreter to invoke
2395 for this command and the interpreter is execed with the name
2396 of the script as argument zero and argument one. If the
2397 setuid or setgid bits are on for this file, then the
2398 interpreter is run with the effective uid and/or gid set
2399 accordingly. This scheme has two major drawbacks. First of
2400 all, using the #! notation forces an exec of the
2401 interpreter even when the call is invoked from the
2402 interpreter which it must exec. This is inefficient since
2403 the interpreter can handle a failed exec much faster than
2404 starting up again. More importantly, setuid and setgid
2405 procedures provide an easy target for intrusion. By linking
2406 a setuid or setgid procedure to a name beginning with a -
2407 the interpreter is fooled into thinking that it is being
2408 invoked with a command line option rather than the name of a
2409 file. When the interpreter is the shell, the user gets a
2410 privileged interactive shell. There is code in ksh to guard
2411 against this simple form of intrusion.
2413 A more reliable way to handle setuid and setgid procedures
2414 is provided with ksh. The technique does not require any
2415 changes to the operating system and provides better
2416 security. Another advantage to this method is that it also
2417 allows scripts which have execute permission but no read
2418 permission to run. Taking away read permission makes
2419 scripts more secure.
2421 The method relies on a setuid root program to authenticate
2422 the request and exec the shell with the correct mode bits to
2423 carry out the task. This shell is invoked with the
2424 requested file already open for reading. A script which
2425 cannot be opened for reading or which has its setuid and/or
2426 setgid bits turned on causes this setuid root program to get
2427 execed. For security reasons, this program is given the
2428 full pathname /etc/suid_exec. A description of the
2429 implementation of the /etc/suid_exec program can be found in
2432 BELL LABORATORIES PROPRIETARY
2433 Not for use or disclosure outside Bell Laboratories except by
2434 written approval of the director of the distributing organization.
2450 a separate paper[18].
2455 ksh is written in ANSI-C as a reusable library. The code
2456 can be compiled with C++ and older K&R C as well. The code
2457 uses the IEEE POSIX 1003.1 and ISO 9945-1 standard[19]
2458 wherever possible so that ksh should be able to run on any
2459 POSIX compliant system. In addition, it is possible to
2460 compile ksh for older systems.
2462 Unlike earlier version of the Bourne shell, ksh treats eight
2463 bit characters transparently without stripping off the
2464 leading bit. There is also a compile time switch to enable
2465 handling multi-byte and multi-width characters sets.
2467 On systems with dynamic libraries, it is possible to add
2468 built-in commands at run time with the built-in command
2469 builtin described earlier. It is also possible to embed ksh
2470 in applications in a manner analogous to tcl.
2475 An example of a ksh script is included in the Appendix.
2476 This one page program is a variant of the UNIX system
2477 grep(1) program. Pattern matching for this version of grep
2478 means shell patterns.
2480 The first half uses the getopts command to find the option
2481 flags. Nearly all options have been implemented. The
2482 second half goes through each line of each file to look for
2485 This program is not intended to serve as a replacement for
2486 grep which has been highly tuned for performance. It does
2487 illustrate the programming power of ksh. Note that no
2488 auxiliary processes are spawned by this script. It was
2489 written and debugged in under two hours. While performance
2490 is acceptable for small files, this program runs at only one
2491 tenth the speed of grep for large files.
2498 BELL LABORATORIES PROPRIETARY
2499 Not for use or disclosure outside Bell Laboratories except by
2500 written approval of the director of the distributing organization.
2518 ksh executes many scripts faster than the System V Bourne
2519 shell; in some cases more than 10 times as fast. The
2520 primary reason for this is that ksh creates fewer processes.
2521 The time to execute a built-in command or a function is one
2522 or two orders of magnitude faster than performing a fork()
2523 and exec() to create a separate process. Command
2524 substitution and commands inside parentheses are performed
2525 without creating another process, unless necessary to
2526 preserve correct behavior.
2528 Another reason for improved performance is the use of the
2529 sfio[20], library for I/O. The sfio library buffers all I/O
2530 and output and buffers are flushed only when required. The
2531 algorithms used in sfio perform better than traditional
2532 versions of standard I/O so that programs that spend most of
2533 their time formatting output may actually perform better
2534 than versions written in C.
2536 Several of the internal algorithms have been changed so that
2537 the number of subroutine calls has been substantially
2538 reduced. ksh uses variable sized hash tables for variables.
2539 Scripts that rely heavily on referencing variables execute
2540 faster. More processing is performed while reading the
2541 script so that execution time is saved while running loops.
2542 These changes are not noticeable for scripts that fork() and
2543 run processes, but they reduce the time that it takes to
2544 interpret commands by more than a factor of two.
2546 Most importantly, ksh provide mechanisms to write
2547 applications that do not require as many processes. The
2548 arithmetic provided by the shell eliminates the need for the
2549 expr command. The pattern matching and substring
2550 capabilities eliminate the need to use sed or awk to process
2553 The architecture of ksh makes it easy to make commands
2554 built-ins without changing the semantics at all. Systems
2555 that have run-time binding of libraries allow applications
2556 to be sped up by supplying the critical programs as shell
2557 built-in commands. Implementations on other systems can add
2558 built-in commands at compile time.
2564 BELL LABORATORIES PROPRIETARY
2565 Not for use or disclosure outside Bell Laboratories except by
2566 written approval of the director of the distributing organization.
2584 The 1988 version of ksh has tens of thousands of regular
2585 users and is a suitable replacement for the Bourne shell.
2586 The 1993 version of ksh is essentially upward compatible
2587 with both the 1988 version of ksh and with the recent IEEE
2588 POSIX and ISO shell standard. The 1993 version offers many
2589 advantages for programming applications, and it has been
2590 rewritten so that it can be used in embedded applications.
2591 It also offers improved performance.
2595 MH-11267-DGK-dgk David G. Korn
2630 BELL LABORATORIES PROPRIETARY
2631 Not for use or disclosure outside Bell Laboratories except by
2632 written approval of the director of the distributing organization.
2696 BELL LABORATORIES PROPRIETARY
2697 Not for use or disclosure outside Bell Laboratories except by
2698 written approval of the director of the distributing organization.
2719 1. S. R. Bourne, An Introduction to the UNIX Shell," BSTJ -
2720 Vol. 57, No. 6 part 2, pages 1947-1972.
2722 2. POSIX - Part 2: Shell and Utilities, IEEE Std 1003.2-
2723 1992, ISO/IEC 9945-2:1992.
2725 3. Al Aho, Brian Kernighan, and Peter Weinberger, The AWK
2726 Programming Language, Addison Wesley, 1988.
2728 4. LLoyd H. Nakatani and Laurence W. Ruedisueli, The FIT
2729 Programming Language Primer, TN 1126-920301-03, 1992.
2731 5. Larry Wall, The PERL Programming Language,
2733 6. John K. Ousterhout, Tcl: An Embeddable Command Language,
2734 Proceedings of the USENIX meeting, pp. ?-?, 1990.
2736 7. S. R. Bourne, An Introduction to the UNIX Shell, Bell
2737 System Technical Journal, Vol. 57, No. 6, Part 2, pp.
2738 1947-1972, July 1978.
2740 8. W. Joy, An Introduction to the C Shell, Unix
2741 Programmer's Manual, Berkeley Software Distribution,
2742 University of California, Berkeley, 1980.
2744 9. Morris Bolsky and David Korn, The KornShell Command and
2745 Programming Language, Prentice Hall, 1989.
2747 10. Jason Levitt, The Korn Shell: An Emerging Standard,
2748 UNIX/World, pp. 74-81, September 1986.
2750 11. Rich Bilancia, Proficiency and Power are Yours With the
2751 Korn Shell, UNIX/World, pp. 103-107, September 1987.
2753 12. John Sebes, Comparing UNIX Shells, UNIX Papers, Edited
2754 by the Waite Group, Howard W. Sams & Co., 1987.
2756 13. T. A. Dolotta and J. R. Mashey, Using the shell as a
2757 Primary Programming Tool, Proc. 2nd. Int. Conf. on
2758 Software Engineering, 1976, pages 169-176.
2762 BELL LABORATORIES PROPRIETARY
2763 Not for use or disclosure outside Bell Laboratories except by
2764 written approval of the director of the distributing organization.
2780 14. J. S. Pendergrast, WKSH - Korn Shell with X-Windows
2783 15. American National Standard for Information Systems -
2784 Programming Language - C, ANSI X3.159-1989.
2786 16. G. S. Fowler, "The Fourth Generation Make," Proceedings
2787 of the Portland USENIX meeting, pp. 159-174, 1985.
2789 17. F. T. Grampp and R. H. Morris, UNIX Operating System
2790 Security, AT&T Bell Labs Tech. Journal, Vol. 63, No. 8,
2791 Part 2, pp.1649-1671, 1984.
2793 18. D. G Korn Parlez-vous Kanji? TM-59554-860602-03, 1986.
2795 19. POSIX - Part 1: System Application Program Interface,
2796 IEEE Std 1003.1-1990, ISO/IEC 9945-1:1990.
2798 20. David Korn and Kiem-Phong Vo, SFIO - A Safe/Fast
2799 Input/Output library, Proceedings of the Summer Usenix,
2828 BELL LABORATORIES PROPRIETARY
2829 Not for use or disclosure outside Bell Laboratories except by
2830 written approval of the director of the distributing organization.
projects / oweals / cde.git / blob