Bourne / Korn Shell (Public Domain)

  • Command syntax
  • The select statement
  • Alias expansion
  • Alternation
  • Shell variables
  • Substitution
  • Expressions
  • Command execution
  • Job Control
  • Interactive Input Line Editing
  • BUGS

  • TEST

  • NAME



    ksh [-st] [-c command] [file [argument ...]]


    This document only summarizes the System V, release 2 shell features. All of the System V features except for ``restricted mode'' are implemented. See also the BUGS section. Features of the Korn shell are described in more detail. Only a subset of the Korn shell features are currently implemented.


    Command syntax

    The ``#'' character begins a one-line comment, unless the ``#'' occurs inside a word. The tokens ``;'', ``|'', ``&'', ``;;'', ``||'', ``&&'', ``('', and ``)'' stand by themselves. A word is a sequence of any other non- whitespace characters, which may also contain quoted strings (quote character are ``''', ``"'', ```'', or a matching ``${ }'' or ``$( )'' pair). A name is an unquoted word made up of letters, digits, or ``_''. Any number of whitespace characters (space and tab) may sepa- rate words and tokens. In the following syntax, { ... }? indicates an optional thing, { ... }* indicates zero or more repetitions, { ... | ... } indicates alternatives. statement: ( list ) { list ; } for name { in { word }* }? do list ; done select name { in { word }* }? do list ; done { while | until } list ; do list ; done if list ; then list ; { elif list ; then list ; }* { else list ; }?fi case name in { ( word { | word } ) list ;; }* esac function name { list ; } name () { list ; } time pipe The opening parenthesis of the pattern is optional. Redirection may occur at the beginning or end of a statement. command: { name=word }* { word }* Redirection may occur anywhere in a command. list: cond cond ; list cond & list cond: pipe pipe && cond pipe || cond pipe: statement { | statement }*

    The select statement

    The select statement provides an automatic method of pre- senting the user with a menu selection from several options. The words given in the list are printed on stan- dard error, each preceded by a number. Typing the number on standard input sets the variable name to the word that was selected. The data that was typed is preserved in a variable called REPLY. The contents of the loop are then executed using the selected value. A new prompt PS3 is used to indicate that a number should be typed in to choose a value from the menu. Menus will continue to be presented until an interrupt is received or end-of-file is typed on input.

    Alias expansion

    Alias expansion occurs when the first word of a statement is a defined alias, except when that alias is already being expanded. It also occurs after the expansion of an alias whose definition ends with a space.


    Csh provides a filename expansion method known as alterna- tion. This has been added into this version of ksh. When performing filename substitution, you can get the shell to create a set of strings for you. For example, `exampl{a,b,c,d,e}' will expand to ``exampla examplb exam- plc exampld example''. A comma separated set of strings in curly braces will be expanded into a set of strings that are passed into the command. The strings are not sorted.

    Shell variables

    The following standard special variables exist: !, #, $, -, ?. _ In interactive use this parameter is set to the last word of the previous command. When a command is executed this parameter is set to the full path of the command and placed in the environment for the command. See also MAILPATH. CDPATH The search path for the cd command. ENV If this variable is set at start-up (after any pro- file files are executed), the expanded value is used as shell start-up file. It typically contains function and alias definitions. FCEDIT The editor used by the fc command. During startup the shell checks the value of FCEDIT, EDITOR and finally VISUAL to try and determine what command line edit mode to use. Note that this is not strictly ksh compatible behaviour. COLUMNS The width to use for the commandline editing (emacs mode only). HISTFILE The name of the file used to store history. If defined, history will be loaded from this file on startup. Also, several invocations of the shell running on the same machine will share history if their HISTFILE variables all point at the same file. HISTSIZE The number of commands normally stored for history, default 128. HOME The default directory for the cd command. IFS Internal field separator, used during substitution and the read command. MAIL If set, the user will be informed of the arrival of mail in the named file. This variable is ignored if the MAILPATH variable is set. MAILCHECK How often, in seconds, the shell will check for mail in the file(s) specified by MAIL or MAILPATH. If 0, the shell checks before each prompt. The default is 600 seconds. MAILPATH A list of files to be checked for mail. The list is colon separated, and each file may be followed by a ? and a message to be printed if new mail has arrived. Command and parameter substitution is performed on the message, and the parameter $_ is set to the name of the file. The default message is ``you have mail in $_''. PATH The search path for executable commands and .'d files. PPID The process number of the parent of the shell. PS1 PS2 PS1 is the primary prompt for interactive shells. Dollar substitution is performed, and ! is replaced with the command number (see fc). PWD OLDPWD The current and previous working directories. RANDOM A random integer. The random number generator may be seeded by assigning an integer value to this variable. SECONDS The number of seconds since the shell timer was started or reset. Assigning an integer value to this variable resets the timer.


    In addition to the System Vr2 substitutions, the following are available. $(command) Like `command`, but no escapes are recognized. $(<file) Equivalent to $(cat file), but without forking. ${#var} The length of the string value of var, or the num- ber of arguments if var is * or @. ${var#pattern} ${var##pattern} If pattern matches the beginning of the value of var, the matched text is deleted from the result of substitution. A single # results in the shortest match, two #'s results in the longest match. ${var%pattern} ${var%%pattern} Like # substitution, but deleting from the end of the value.


    Expressions can be used with the let command, as numeric arguments to the test command, and as the value of an assignment to an integer variable. Expression may contain alpha-numeric variable identifiers and integer constants and may be combined with the follow- ing operators: == != <= < > >= + - * / % ! ( )

    Command execution

    After evaluation of keyword assignments and arguments, the type of command is determined. A command may execute a shell function, a shell built-in, or an executable file. Any keyword assignments are then performed according to the type of command. In function calls assignments are local to the function. Assignments in built-in commands marked with a |- persist, otherwise they are temporary. Assignments in executable commands are exported to the sub-process executing the command. Even on systems where the exec() family does not support #! notation for scripts, ksh can be configured to fake it. There are several built-in commands. : Only expansion and assignment are performed. This is the default if a command has no arguments. . file Execute the commands in file without forking. The file is searched in the directories of $PATH. Passing arguments is not implemented. alias [name=value ...] Without arguments, alias lists all aliases and their values. For any name without a value, its value is listed. Any name with a value defines an alias, see "Alias Expansion" above. Korn's tracked aliases are not implemented, but System V command hashing is (see "hash"). alias -d [name=value ...] Directory aliases for tilde expansion, eg. alias -d fac=/usr/local/usr/facilities cd ~fac/bin break [levels] builtin command arg ... Command is executed as a built-in command. cd [path] Set the working directory to path. If the parame- ter CDPATH is set, it lists the search path for the directory containing path. A null path means the current directory. If path is missing, the home directory ($HOME) is used. If path is -, the pre- vious working directory is used. If path is .., the shell changes directory to the parent direc- tory, as determined from the value of PWD. The PWD and OLDPWD variables are reset. cd old new The string new is substituted for old in the cur- rent directory, and the shell attempts to change to the new directory. continue [levels] echo ... Echo is replaced with the alias echo='print' in the Korn shell. eval command ... exec command arg ... The executable command is executed without forking. If no arguments are given, any IO redirection is permanent. exit [status] fc [-e editor] [-lnr] [first [last]] First and last select commands. Commands can be selected by history number, or a string specifying the most recent command starting with that string. The -l option lists the command on stdout, and -n inhibits the default command numbers. The -r option reverses the order of the list. Without -l, the selected commands can be edited by the editor specified with the -e option, or if no -e is speci- fied, the $FCEDIT editor, then executed by the shell. fc -e - [-g] [old=new] [command] Re-execute the selected command (the previous com- mand by default) after performing the optional sub- stitution of old with new. If -g is specified, all occurrences of old are replaced with new. This command is usually accessed with the predefined alias r=``fc -e -''. getopts See the attached manual page. hash [-r] [name ...] Without arguments, any hashed executable command pathnames are listed. The -r flag causes all hashed commands to be removed. Each name is searched as if it were a command name and added to the hash table if it is an executable command. kill [-signal] process ... Send a signal (TERM by default) to the named process. The signal may be specified as a number or a mnemonic from <signal.h> with the SIG prefix removed. let [expression ...] Each expression is evaluated, see "Expressions" above. A zero status is returned if the last expression evaluates to a non-zero value, otherwise a non-zero status is returned. Since may expres- sions need to be quoted, (( expr )) is syntactic sugar for let "expr". print [-nreun] [argument ...] Print prints its arguments on the standard output, separated by spaces, and terminated with a newline. The -n option eliminates the newline. By default, certain C escapes are translated. These include \b, \f, \n, \r, \t, \v, and \### (# is an octal digit). \c is equivalent to the -n option. This expansion may be inhibitted with the -r option, and may be re-enabled with the addition of the -e option. read [-run] name ... The first variable name may be of the form name?prompt. readonly [name ...] return [status] set [+-[a-z]] [+-o keyword] ... Set (-) or clear (+) a shell option: -a allexport all new variable are created with export attribute -e errexit exit on non-zero sta- tus [incorrect] bgnice background jobs are run with lower priority emacs BRL emacs-like line editing ignoreeof shell will not exit of EOF, must use exit -k keyword variable assignments are recognized anywhere in command markdirs [not implemented] -m monitor job control enabled (default for interactive shell) -n noexec compile input but do not execute (ignored if interactive) -f noglob don't expand file- names -u nounset dollar expansion of unset variables is an error -v verbose echo shell commands on stdout when compiling -h trackall add command pathnames to hash table vi VI-like line editing -x xtrace echo simple commands while executing set [--] arg ... Set shell arguments. shift [number] test See the attached manual page. times trap [handler] [signal ...] typeset [+-irtx] [name[=value] ...] If no arguments are given, lists all variables and their attributes. If options but no names are given, lists variables with specified attributes, and their values if unless ``+'' is used. If names are given, set the attributes of the named vari- ables. Variables may also be assigned a value. If used inside a function, the created variable are local to the function. The attributes are as follows. -iThe variable's value is stored as an integer. -xThe variable is exported to the environment. -rThe variable is read-only cannot be reassigned a value. -tTrace (not implemented). -fList functions instead of variable. ulimit [ -<OZ> ] [ n ] -c Impose a size limit of n blocks on the size of core dumps. -d Impose a size limit of n blocks on the size of the data area. -f Impose a size limit of n blocks on files writ- ten by the shell and its child processes (files of any size may be read). -m Impose a soft limit of n blocks on the size of physical memory. -t Impose a time limit of n seconds to be used by each process. If no option is given, -f is assumed. If n is omitted, the current limit is printed. As far as ulimit is concerned, a ``block'' is 512 bytes. You may lower your own resource limit, but only a super-user (see su(1M)) can raise a limit. umask [value] unalias name ... The aliases for the given names are removed. unset [-f] name ... wait [process-id] whence [-v] name ... For each name, the type of command is listed. The -v flag causes function and alias values to be listed.

    Job Control

    Job control features are enabled by the -m or -o monitor flags. When job control is enabled, and the system sup- ports job control, background commands and foreground com- mands that have been stopped (usually by a SIGTSTP signal generated by typing ^Z) are placed into separate individ- ual process groups. The following commands are used to manipulate these process groups: jobs Display information about the controlled jobs. The job number is given preceeded by a percent sign, followed by a plus sign if it is the ``current job'', or by a minus sign if it is the ``previous job'', then the process group number for the job, then the command. kill [-signal] job ... Send a signal (TERM by default) to the named job process group. fg [ job ] Resume the stopped foreground job in the foreground. If the process group n is not specified then the ``current job'' is resumed. bg [ job ] Resume the stopped foreground job in the background. If the process group n is not specified then the ``current job'' is resumed. The fg, bg, kill, and wait commands may refer to jobs with the following ``percent'' sequences. The percent sign is optional with the fg and bg commands. %+(%-) If there is a ``current job'' (``previous job''), then that job is selected. %n If the specified job number is one of the known jobs, then that job is selected. %string If the string matches the initial part of a job's command, then that job is selected. %?string As above, but the string may match any portion of the command. If the system does not support job control, monitor mode enables job reporting. The jobs and kill commands func- tions as above, and you will be informed when background jobs complete. Fg and bg are not available.

    Interactive Input Line Editing

    When the emacs option is set, interactive input line edit- ing is enabled. This mode is slightly different from the emacs mode in AT&T's KornShell. In this mode various editing commands (typically bound to one or more control characters) cause immediate actions without waiting for a new-line. Several editing commands are bound to particu- lar control characters when the shell is invoked; these bindings can be changed using the following commands: bind The current bindings are listed. bind [ string ] = [ editing-command ] The specified editing command is bound to the given string, which should con- sist of a control character (which may be written using ``caret notation'' ^x), optionally preceded by one of the two prefix characters. Future input of the string will cause the editing command to be immediately invoked. Note that although only two prefix characters (normal ESC and ^X) are supported, some multi-character sequences can be supported: bind '^[['=prefix-2 bind '^XA'=up-history bind '^XB'=down-history bind '^XC'=forward-char bind '^XD'=backward-char will bind the arrow keys on an ANSI terminal, or xterm. Of course some escape sequences won't work out quite that nicely. bind -m [ string ] = [ substitute ] The specified input string will after- wards be immediately replaced by the given substitute string, which may contain editing commands. The following editing commands are available; first the command name is given followed by its default binding (if any) using caret notation (note that the ASCII ESC charac- ter is written as ^[), then the editing function performed is described. Note that editing command names are used only with the bind command. Furthermore, many editing commands are useful only on terminals with a visible cur- sor. The default bindings were chosen to resemble corre- sponding EMACS key bindings. The users tty characters (eg. erase) are bound to reasonable substitutes. abort ^G Useful as a response to a request for a search- history pattern in order to abort the search. auto-insert Simply causes the charac- ter to appear as literal input. (Most ordinary characters are bound to this.) backward-char ^B Moves the cursor backward one character. backward-word ^[b Moves the cursor backward to the beginning of a word. beginning-of-line ^A Moves the cursor to the beginning of the input line (after the prompt string). complete ^[^[ Automatically completes as much as is unique of the hashed command name or the file name containing the cursor. If the entire remaining command or file name is unique a space is printed after its comple- tion, unless it is a directory name in which case / is postpended. If there is no hashed command or file name with the cur- rent partial word as its prefix, a bell character is output (usually causing a ``beep''). complete-command ^X^[ Automatically completes as much as is unique of the hashed command name having the partial word up to the cursor as its prefix, as in the complete command described above. Only command and function names seen since the last hash -r command are available for completion; the hash command may be used to register additional names. complete-file ^[^X Automatically completes as much as is unique of the file name having the par- tial word up to the cursor as its prefix, as in the complete command described above. copy-last-arg ^[_ The last word of the pre- vious command is inserted at the cursor. Note I/O redirections do not count as words of the command. delete-char-backward ERASE Deletes the character before the cursor. delete-char-forward Deletes the character after the cursor. delete-word-backward ^[ERASE Deletes characters before the cursor back to the beginning of a word. delete-word-forward ^[d Deletes characters after the cursor up to the end of a word. down-history ^N Scrolls the history buffer forward one line (later). Each input line originally starts just after the last entry in the history buffer, so down-history is not useful until either search-history or up- history has been per- formed. end-of-line ^E Moves the cursor to the end of the input line. eot ^_ Acts as an end-of-file; this is useful because edit-mode input disables normal terminal input canonicalization. eot-or-delete ^D Acts as eot if alone on a line; otherwise acts as delete-char-forward. exchange-point-and-mark ^X^X Places the cursor where the mark is, and sets the mark to where the cursor was. forward-char ^F Moves the cursor forward one position. forward-word ^[f Moves the cursor forward to the end of a word. kill-line KILL Deletes the entire input line. kill-to-eol ^K Deletes the input from the cursor to the end of the line. kill-region ^W Deletes the input between the cursor and the mark. list ^[? Prints a sorted, colum- nated list of hashed com- mand names or file names (if any) that can complete the partial word contain- ing the cursor. Directory names have / postpended to them, and executable file names are followed by *. list-command ^X? Prints a sorted, colum- nated list of hashed com- mand names (if any) that can complete the partial word containing the cur- sor. list-file Prints a sorted, colum- nated list of file names (if any) that can complete the partial word contain- ing the cursor. File type indicators are postpended as described under list above. newline ^J and ^M Causes the current input line to be processed by the shell. (The current cursor position may be anywhere on the line.) newline-and-next ^O Causes the current input line to be processed by the shell, and the next line from history becomes the current line. This is only useful after an up- history or search-history. no-op QUIT Does nothing. prefix-1 ^[ Introduces a 2-character command sequence. prefix-2 ^X Introduces a 2-character command sequence. quote ^^ The following character is taken literally rather than as an editing command. redraw ^L Reprints the prompt string and the current input line. search-character ^] Search forward in the cur- rent line for the next keyboard character. search-history ^R Enter incremental search mode. The internal his- tory list is searched backwards for commands matching the input. An initial ``^'' in the search string anchors the search. The escape key will leave search mode. Other commands will be executed after leaving search mode (unless of course they are prefixed by escape, in which case they will almost certainly do the wrong thing). Suc- cessive search-history commands continue search- ing backward to the next previous occurrence of the pattern. The history buffer retains only a finite number of lines; the oldest are discarded as necessary. set-mark-command ^]<space> Search forward in the cur- rent line for the next keyboard character. stuff On systems supporting it, pushes the bound character back onto the terminal input where it may receive special processing by the terminal handler. stuff-reset Acts like stuff, then aborts input the same as an interrupt. transpose-chars ^T Exchanges the two charac- ters on either side of the cursor, or the two previ- ous characters if the cur- sor is at end of line. up-history ^P Scrolls the history buffer backward one line (ear- lier). yank ^Y Inserts the most recently killed text string at the current cursor position. yank-pop ^[y Immediately after a yank, replaces the inserted text string with the next pre- vious killed text string.


    ~/.profile /etc/profile


    Sh(1) on System V or Sun OS. UNIX Shell Programming, Stephan G. Kochan, Patrick H. Wood, Hayden. KornShell: Command and Programming Language (not yet pub- lished), Morris Bolsky and David Korn.


    Based on the public domain 7th edition Bourne shell. System V and Korn modifications by Eric Gisin, with con- tributions by Ron Natalie, Arnold Robbins, Doug Gwyn, Erik Baalbergen, AT&T (getopt(3)), John McMillan, Simon Gerraty and Peter Collinson.


    Csh-style alternations are implemented. Variable arrays are not implemented. Variable attributes other than inte- ger are not implemented. The ERR and EXIT traps are not implemented for functions. Alias expansion is inhibited at the beginning of an alias definition in the AT&T ver- sion. Korn evaluates expressions differently [elaborate].


    Interactive shells may occasionally hang while waiting for a job in the BSD version. The 8th bit is stripped in emacs mode. Quoting double-quote (") characters inside back-quote (`) inside double-quotes does not behave properly. Why are you doing this? The emacs mode can ``lose'' stty command done by the user. Unsetting special variables may cause unexpected results. Functions declared as having local scope really have global scope. Here documents inside functions do not work correctly. Exit on error (set -e or set -o errexit) does not work correctly.


    test - test condition (Korn and 8th edition)


    test expression [ expression ]


    Test evaluates the expression and returns zero status if true, and non-zero status otherwise. It is normally used as the controlling command of the if and while statements. The following basic expressions are available. -r file file exists and is readable -w file file exists and is writable -x file file exists and is executable -f file file is a regular file -d file file is a directory -c file file is a character special device -b file file is a block spe- cial device -p file file is a named pipe -u file file mode has setuid bit -g file file mode has setgid bit -k file file mode has sticky bit -s file file is not empty -L file file is a symbolic link -S file file is a socket file -nt file first file is newer than second file file -ot file first file is older than second file file -ef file first file is the same file as second file -t filedes file descriptor is a tty device string string is not null -z string string is null -n string string is not null string = string strings are equal string != string strings are not equal number -eq number numbers compare equal number -ne number numbers compare not equal number -ge number numbers compare greater than or equal number -gt number numbers compare greater than number -le number numbers compare less than or equal number -lt number numbers compare less than The above basic expressions may be combined with the fol- lowing operators. expr -o expr logical or expr -a expr logical and ! expr logical not ( expr ) grouping


    Erik Baalbergen. Modified by Arnold Robbins.



    getopts - parse command options


    getopts optstring name [arg ...]


    getopts is used by shell procedures to parse positional parameters and to check for legal options. It supports all applicable rules of the command syntax standard (see Rules 3-10, intro(1)). It should be used in place of the getopt(1) command. (See the WARNING, below.) optstring must contain the option letters the command using getopts will recognize; if a letter is followed by a colon, the option is expected to have an argument which should be separated from it by white space. Each time it is invoked, getopts will place the next option in the shell variable name and the index of the next argument to be processed in the shell variable OPTIND. Whenever the shell or a shell procedure is invoked, OPTIND is initialized to 1. When an option requires an option-argument, getopts places it in the shell variable OPTARG. If an illegal option is encountered, ? will be placed in name. When the end of the options is encountered, getopts exits with a non-zero exit status. The special option ``--'' may be used to delimit the end of the options. By default, getopts parses the positional parameters. If extra arguments (arg ...) are given on the getopts command line, getopts will parse them instead. So all new commands will adhere to the command syntax standard described in intro(1), they should use getopts(1) or getopt(3C) to parse positional parameters and check for options that are legal for that command (see WARNINGS, below).


    The following fragment of a shell program shows how one might process the arguments for a command that can take the options a or b, as well as the option o, which requires an option-argument: while getopts abo: c do case $c in a|b) FLAGS=$FLAGS$c;; o) OARG=$OPTARG;; \?) echo $USAGE 1>&2 exit 2;; esac done shift OPTIND-1 This code will accept any of the following as equivalent: cmd -a -b -o "xxx z yy" file cmd -a -b -o "xxx z yy" -- file cmd -ab -o "xxx z yy" file cmd -ab -o "xxx z yy" -- file


    intro(1), sh(1). getopt(3C) in the Programmer's Reference Manual. UNIX System V Release 3.0 Release Notes.


    Although the following command syntax rule (see intro(1)) relaxations are permitted under the current implementa- tion, they should not be used because they may not be sup- ported in future releases of the system. As in the EXAM- PLE section above, a and b are options, and the option o requires an option-argument: cmd -aboxxx file (Rule 5 violation: options with option-arguments must not be grouped with other options) cmd -ab -oxxx file (Rule 6 violation: there must be white space after an option that takes an option-argument) Changing the value of the shell variable OPTIND or parsing different sets of arguments may lead to unexpected results.


    getopts prints an error message on the standard error out- put when it encounters an option letter not included in optstring.