+//usage:#define df_trivial_usage
+//usage: "[-Pk"
+//usage: IF_FEATURE_HUMAN_READABLE("mh")
+//usage: IF_FEATURE_DF_FANCY("ai] [-B SIZE")
+//usage: "] [FILESYSTEM]..."
+//usage:#define df_full_usage "\n\n"
+//usage: "Print filesystem usage statistics\n"
+//usage: "\n -P POSIX output format"
+//usage: "\n -k 1024-byte blocks (default)"
+//usage: IF_FEATURE_HUMAN_READABLE(
+//usage: "\n -m 1M-byte blocks"
+//usage: "\n -h Human readable (e.g. 1K 243M 2G)"
+//usage: )
+//usage: IF_FEATURE_DF_FANCY(
+//usage: "\n -a Show all filesystems"
+//usage: "\n -i Inodes"
+//usage: "\n -B SIZE Blocksize"
+//usage: )
+//usage:
+//usage:#define df_example_usage
+//usage: "$ df\n"
+//usage: "Filesystem 1K-blocks Used Available Use% Mounted on\n"
+//usage: "/dev/sda3 8690864 8553540 137324 98% /\n"
+//usage: "/dev/sda1 64216 36364 27852 57% /boot\n"
+//usage: "$ df /dev/sda3\n"
+//usage: "Filesystem 1K-blocks Used Available Use% Mounted on\n"
+//usage: "/dev/sda3 8690864 8553540 137324 98% /\n"
+//usage: "$ POSIXLY_CORRECT=sure df /dev/sda3\n"
+//usage: "Filesystem 512B-blocks Used Available Use% Mounted on\n"
+//usage: "/dev/sda3 17381728 17107080 274648 98% /\n"
+//usage: "$ POSIXLY_CORRECT=yep df -P /dev/sda3\n"
+//usage: "Filesystem 512-blocks Used Available Capacity Mounted on\n"
+//usage: "/dev/sda3 17381728 17107080 274648 98% /\n"
+