zsh - Parameters

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# Parameters

A parameter has a name, a value, and a number of attributes. A name may be any sequence of alphanumeric characters and `_`'s, or the single characters `*`, `@`, `#`, `?`, `-`, `$`, or `!`. The value may be either a scalar (a string), an integer, or an array. To assign a scalar or integer value to a parameter, use the `typeset` builtin. To assign an array value, use ``set -A name value ...'`. The value of a parameter may also be assigned by writing:

`name=value ...`

If the integer attribute, ``-i'`, is set for name, the value is subject to arithmetic evaluation.

## Array Parameters

The value of an array parameter may be assigned by writing:

name=(value ...) ...

Individual elements of an array may be selected using a subscript. A subscript of the form `[exp]` selects the single element exp, where exp is an arithmetic expression which will be subject to arithmetic expansion as if it were surrounded by `$((...))`. The elements are numbered beginning with 1 unless the `KSH_ARRAYS` option is set when they are numbered from zero.

A subscript of the form `[*]` or `[@]` evaluates to all elements of an array; there is no difference between the two except when they appear within double quotes. `"$foo[*]"` evaluates to `"$foo[1] $foo[2] ..."`, while `"$foo[@]"` evaluates to `"$foo[1]"` `"$foo[2]"`, etc.

A subscript of the form `[exp1,exp2]` selects all elements in the range exp1 to exp2, inclusive. If one of the subscripts evaluates to a negative number, say `-n`, then the n'th element from the end of the array is used. Thus `$foo[-3]` is the third element from the end of the array `foo`, and `$foo[1,-1]` is the same as `$foo[*]`.

Subscripting may also be performed on non-array values, in which case the subscripts specify a substring to be extracted. For example, if `FOO` is set to `foobar`, then `echo $FOO[2,5]` prints `ooba`.

Subscripts may be used inside braces used to delimit a parameter name, thus `${foo[2]}` is equivalent to `$foo[2]`. If the `KSH_ARRAYS` option is set, the braced form is the only one that will work, the subscript otherwise not being treated specially.

If a subscript is used on the left side of an assignment the selected range is replaced by the expression on the right side.

If the opening bracket or the comma is directly followed by an opening parenthesis the string up to the matching closing parenthesis is considered to be a list of flags. The flags currently understood are:

`e`
  This option has no effect and retained for backward compatibility only.
`w`
  If the parameter subscripted is a scalar, then this flag makes subscription work on a per-word basis instead of characters.
`s:string:`
  Defines the string that separates words (for use with the `w` flag).
`p`
  Recognize the same escape sequences as the `print` builtin in the string argument of a subsequent `s` flag.
`f`
  If the parameter subscripted is a scalar than this flag makes subscription work on a per-line basis instead of characters. This is a shorthand for `pws:\n:`.
`r`
  If this flag is given the exp is taken as a pattern and the result is the first matching array element, substring or word (if the parameter is an array, if it is a scalar, or if it is a scalar and the `w` flag is given, respectively); note that this is like giving a number: `$foo[(r)??,3]` and `$foo[(r)??,(r)f*]` work.
`R`
  Like `r`, but gives the last match.
`i`
  Like `r`, but gives the index of the match instead; this may not be combined with a second argument.
`I`
  Like `i`, but gives the index of the last match.
`n:expr:`
  If combined with `r`, `R`, `i`, or `I`, makes them return the n'th or n'th last match (if expr evaluates to n).

## Positional Parameters

Positional parameters are set by the shell on invocation, by the `set` builtin, or by direct assignment. The parameter n, where n is a number, is the n'th positional parameter. The parameters `*`, `@`, and `argv` are arrays containing all the positional parameters; thus `argv[n]`, is equivalent to simply n.

## Parameters Set By The Shell

The following parameters are automatically set by the shell:

`!`
  The process id of the last background command invoked.
`#`
  The number of positional parameters in decimal.
`ARGC`
  Same as `#`. It has no special meaning in sh/ksh compatibility mode.
`$`
  The process id of this shell.
`-`
  Flags supplied to the shell on invocation or by the `set` or `setopt` commands.
`*`
  An array containing the positional parameters.
`argv`
  Same as `*`. It has no special meaning in sh/ksh compatibility mode.
`@`
  Same as `argv[@]` but it can be used in sh/ksh compatibility mode.
`?`
  The exit value returned by the last command.
`status`
  Same as `?`. It has no special meaning in sh/ksh compatibility mode.
`_`
  The last argument of the previous command. Also, this parameter is set in the environment of every command executed to the full pathname of the command.
`EGID`
  The effective group id of the shell process. If you have sufficient privileges, you may change the effective group id of the shell process by assigning to this parameter. Also (assuming sufficient privileges), you may start a single command with a different effective group id by: `(EGID=egid ; command)`
`EUID`
  The effective user id of the shell process. If you have sufficient privileges, you may change the effective user id of the shell process by assigning to this parameter. Also (assuming sufficient privileges), you may start a single command with a different effective user id by: `(EUID=euid ; command)`
`ERRNO`
  The value of `errno` as set by the most recently failed system call. This value is system dependent and is intended for debugging purposes.
`GID`
  The group id of the shell process. If you have sufficient privileges, you may change the group id of the shell process by assigning to this parameter. Also (assuming sufficient privileges), you may start a single command under a different group id by: `(GID=gid ; command)`
`HOST`
  The current hostname.
`LINENO`
  The line number of the current line within the current script being executed.
`LOGNAME`
  If the corresponding variable is not set in the environment of the shell, it is initialized to the login name corresponding to the current login session. This parameter is exported by default but this can be disabled using the `typeset` builtin.
`MACHTYPE`
  The machine type (microprocessor class or machine model), as determined at compile time.
`OLDPWD`
  The previous working directory.
`OPTARG`
  The value of the last option argument processed by the `getopts` command.
`OPTIND`
  The index of the last option argument processed by the `getopts` command.
`OSTYPE`
  The operating system, as determined at compile time.
`PPID`
  The process id of the parent of the shell.
`PWD`
  The present working directory.
`RANDOM`
  A random integer from 0 to 32767, newly generated each time this parameter is referenced. The random number generator can be seeded by assigning a numeric value to `RANDOM`.
`SECONDS`
  The number of seconds since shell invocation. If this parameter is assigned a value, then the value returned upon reference will be the value that was assigned plus the number of seconds since the assignment.
`SHLVL`
  Incremented by one each time a new shell is started.
`signals`
  An array containing the names of the signals.
`TTY`
  The name of the tty associated with the shell, if any.
`TTYIDLE`
  The idle time of the tty associated with the shell in seconds or -1 if there is no such tty.
`UID`
  The user id of the shell process. If you have sufficient privileges, you may change the user id of the shell by assigning to this parameter. Also (assuming sufficient privileges), you may start a single command under a different user id by: `(UID=uid ; command)`
`USERNAME`
  The username corresponding to the user id of the shell process. If you have sufficient privileges, you may change the username (and also the user id and group id) of the shell by assigning to this parameter. Also (assuming sufficient privileges), you may start a single command under a different username (and user id and group id) by: `(USERNAME=username ; command)`
`VENDOR`
  The vendor, as determined at compile time.
`ZSHNAME`
`ZSH_NAME`
  Expands to the basename of the command used to invoke this instance of zsh.
`ZSH_VERSION`
  The version number of this zsh.

## Parameters Used By The Shell

The following parameters are used by the shell:

`ARGV0`
  If exported, its value is used as argv[0] of external commands. Usually used in constructs like ``ARGV0=emacs nethack'`.
`BAUD`
  The baud rate of the current connection. Used by the line editor update mechanism to compensate for a slow terminal by delaying updates until necessary. This may be profitably set to a lower value in some circumstances, e.g. for slow modems dialing into a communications server which is connected to a host via a fast link; in this case, this variable would be set by default to the speed of the fast link, and not the modem. This parameter should be set to the baud rate of the slowest part of the link for best performance. The compensation mechanism can be turned off by setting the variable to zero.
`cdpath (CDPATH)`
  An array (colon-separated list) of directories specifying the search path for the `cd` command.
`COLUMNS`
  The number of columns for this terminal session. Used for printing select lists and for the line editor.
`DIRSTACKSIZE`
  The maximum size of the directory stack. If the stack gets larger than this, it will be truncated automatically. This is useful with the `AUTO_PUSHD` option.
`FCEDIT`
  The default editor for the `fc` builtin.
`fignore (FIGNORE)`
  An array (colon-separated list) containing the suffixes of files to be ignored during filename completion. However, if the completion generates only files which would match if this variable would be ignored, than these files are completed anyway.
`fpath (FPATH)`
  An array (colon-separated list) of directories specifying the search path for function definitions. This path is searched when a function with the ``-u'` attribute is referenced. If an executable file is found, then it is read and executed in the current environment.
`histchars`
  Three characters used by the shell's history and lexical analysis mechanism. The first character signals the start of a history substitution (default `!`). The second character signals the start of a quick history substitution (default `^`). The third character is the comment character (default `#`).
`HISTCHARS`
  Depreciated. Use `histchars`.
`HISTFILE`
  The file to save the history in when an interactive shell exits. If unset, the history is not saved.
`HISTSIZE`
  The maximum size of the history list.
`HOME`
  The default argument for the `cd` command.
`IFS`
  Internal field separators, normally space, tab, and newline, that are used to separate words which result from command or parameter substitution and words read by the `read` builtin. Any characters from the set space, tab and newline that appear in the `IFS` are called IFS white space. One or more IFS white space characters or one non-IFS white space character together with any adjacent IFS white space character delimit a field. If an IFS white space character appears twice consecutively in the `IFS`, this character is treated as if it were not an IFS white space character.
`KEYTIMEOUT`
  The time the shell waits, in hundredths of seconds, for another key to be pressed when reading bound multi-character sequences.
`LANG`
  This variable determines the locale category for any category not specifically selected via a variable starting with `LC_`.
`LC_ALL`
  This variable overrides the value of the `LANG` variable and the value of any of the other variables starting with `LC_`.
`LC_COLLATE`
  This variable determines the locale category for character collation information within ranges in glob brackets and for sorting.
`LC_CTYPE`
  This variable determines the locale category for character handling functions.
`LC_MESSAGES`
  This variable determines the language in which messages should be written. Note that zsh does not use message catalogs.
`LC_TIME`
  This variable determines the locale category for date and time formatting in promt escape sequences.
`LINES`
  The number of lines for this terminal session. Used for printing select lists and for the line editor.
`LISTMAX`
  In the line editor, the number of filenames to list without asking first. If set to zero, the shell asks only if the listing would scroll off the screen.
`LOGCHECK`
  The interval in seconds between checks for login/logout activity using the `watch` parameter.
`MAIL`
  If this parameter is set and `mailpath` is not set, the shell looks for mail in the specified file.
`MAILCHECK`
  The interval in seconds between checks for new mail.
`mailpath (MAILPATH)`
  An array (colon-separated list) of filenames to check for new mail. Each filename can be followed by a `?` and a message that will be printed. The message will undergo parameter expansion, command substitution and arithmetic substitution with the variable `$_` defined as the name of the file that has changed. The default message is ``You have new mail'`. If an element is a directory instead of a file the shell will recursively check every file in every subdirectory of the element.
`manpath (MANPATH)`
  An array (colon-separated list) whose value is not used by the shell. The `manpath` array can be useful, however, since setting it also sets `MANPATH`, and vice versa.
`NULLCMD`
  The command name to assume if a redirection is specified with no command. Defaults to `cat`. For sh/ksh-like behaviour, change this to `:`. For csh-like behaviour, unset this parameter; the shell will print an error message if null commands are entered.
`path (PATH)`
  An array (colon-separated list) of directories to search for commands. When this parameter is set, each directory is scanned and all files found are put in a hash table.
`POSTEDIT`
  This string is output whenever the line editor exits. It usually contains termcap strings to reset the terminal.
`PS1`
  The primary prompt string, printed before a command is read; the default is ``%m%# '`. If the escape sequence takes an optional integer, it should appear between the `%` and the next character of the sequence. The following escape sequences are recognized:
  `%%`
    A `%`.
  `%)`
    A `)`.
  `%d`
  `%/`
    Present working directory (`$PWD`).
  `%~`
    `$PWD`. If it has a named directory as its prefix, that part is replaced by a `~` followed by the name of the directory. If it starts with `$HOME`, that part is replaced by a `~`.
  `%c`
  `%.`
  `%C`
    Trailing component of `$PWD`. An integer may follow the `%` to get more than one component. Unless `%C` is used, tilde expansion is performed first.
  `!`
  `%h`
  `%!`
    Current history event number.
  `%M`
    The full machine hostname.
  `%m`
    The hostname up to the first ``.'`. An integer may follow the `%` to specify how many components of the hostname are desired.
  `%S (%s)`
    Start (stop) standout mode.
  `%U (%u)`
    Start (stop) underline mode.
  `%B (%b)`
    Start (stop) boldface mode.
  `%t`
  `%@`
    Current time of day, in 12-hour, am/pm format.
  `%T`
    Current time of day, in 24-hour format.
  `%*`
    Current time of day in 24-hour format, with seconds.
  `%n`
    `$USERNAME`.
  `%w`
    The date in day-dd format.
  `%W`
    The date in mm/dd/yy format.
  `%D`
    The date in yy-mm-dd format.
  `%D{string}`
    string is formatted using the `strftime` function. See `strftime(3)` for more details, if your system has it.
  `%l`
    The line (tty) the user is logged in on.
  `%?`
    The return code of the last command executed just before the prompt.
  `%_`
    The status of the parser, i.e. the shell constructs (like `if` and `for`) that have been started on the command line. If given an integer number, that many strings will be printed; zero or no integer means print as many as there are.
  `%E`
    Clears to end of line.
  `%#`
    A `#` if the shell is running as root, a `%` if not. Equivalent to `%(#.#.%%)`
  `%v`
    The value of the first element of the `psvar` array parameter. Following the `%` with an integer gives that element of the array.
  `%{...%}`
    Include a string as a literal escape sequence. The string within the braces should not change the cursor position.
  `%(x.true-text.false-text)`
    Specifies a ternary expression. The character following the `x` is arbitrary; the same character is used to separate the text for the true result from that for the false result. The separator may not appear in the `true-text`, except as part of a `%` sequence. A `)` may appear in the `false-text` as a `%)`. `true-text` and `false-text` may both contain contain arbitrarily-nested escape sequences, including further ternary expressions. The left parenthesis may be preceded or followed by a positive integer `n`, which defaults to zero. The test character `x` may be any of the following:
    `c`
    `.`
    `~`
      True if the current path, with prefix replacement, has at least n elements.
    `/`
    `C`
      True if the current absolute path has at least n elements.
    `t`
      True if the time in minutes is equal to n.
    `T`
      True if the time in hours is equal to n.
    `d`
      True if the day of the month is equal to n.
    `D`
      True if the month is equal to n (January = 0).
    `w`
      True if the day of the week is equal to n (Sunday = 0).
    `?`
      True if the exit status of the last command was n.
    `#`
      True if the effective uid of the current process is n.
    `g`
      True if the effective gid of the current process is n.
    `L`
      True if the `SHLVL` parameter is at least n.
    `S`
      True if the `SECONDS` parameter is at least n.
    `v`
      True if the array `psvar` has at least n elements.
    `_`
      True if at least n shell constructs were started.
    `%<string<`
    `%>string>`
    `%[xstring]`
      Specifies truncation behaviour. The third form is equivalent to `%xstringx`, i.e. `x` may be `<` or `>`. The numeric argument, which in the third form may appear immediately after the `[`, specifies the maximum permitted length of the various strings that can be displayed in the prompt. If this integer is zero, or missing, truncation is disabled. Truncation is initially disabled. The forms with `<` truncate at the left of the string, and the forms with `>` truncate at the right of the string. For example, if the current directory is ``/home/pike'`, the prompt `%8<..<%/` will expand to ``..e/pike'`. The `string` will be displayed in place of the truncated portion of any string. In this string, the terminating character (`<`, `>` or `]`), or in fact any character, may be quoted by a preceding `\`. `%` sequences are not treated specially. If the `string` is longer than the specified truncation length, it will appear in full, completely replacing the truncated string.
`PS2`
  The secondary prompt, printed when the shell needs more information to complete a command. Recognizes the same escape sequences as `$PS1`. The default is ``%_> '`.
`PS3`
  Selection prompt used within a `select` loop. Recognizes the same escape sequences as `PS1`. The default is ``?# '`.
`PS4`
  The execution trace prompt. Default is ``+ '`.
`PROMPT`
`PROMPT2`
`PROMPT3`
`PROMPT4`
  Same as `PS1`, `PS2`, `PS3`, and `PS4`, respectively. These parameters do not have any special meaning in sh/ksh compatibility mode.
`psvar (PSVAR)`
  An array (colon-separated list) whose first nine values can be used in `PROMPT` strings. Setting `psvar` also sets `PSVAR`, and vice versa.
`prompt`
  Same as `PS1`. It has no special meaning in sh/ksh compatibility mode.
`READNULLCMD`
  The command name to assume if a single input redirection is specified with no command. Defaults to `more`.
`REPORTTIME`
  If nonzero, commands whose combined user and system execution times (measured in seconds) are greater than this value have timing statistics printed for them.
`RPROMPT`
`RPS1`
  This prompt is displayed on the right-hand side of the screen when the primary prompt is being displayed on the left. This does not work if the `SINGLELINEZLE` option is set. Recognizes the same escape sequences as `PROMPT`.
`SAVEHIST`
  The maximum number of history events to save in the history file.
`SPROMPT`
  The prompt used for spelling correction. The sequence `%R` expands to the string which presumably needs spelling correction, and `%r` expands to the proposed correction. All other `PROMPT` escapes are also allowed.
`STTY`
  If this parameter is set in a command's environment, the shell runs the `stty` command with the value of this parameter as arguments in order to set up the terminal before executing the command. The modes apply only to the command, and are reset when it finishes or is suspended. If the command is suspended and continued later with the `fg` or `wait` builtins it will see the modes specified by `STTY`, as if it were not suspended. This (intentionally) does not apply if the command is continued via `kill -CONT`. `STTY` is ignored if the command is run in the background, or if it is in the environment of the shell but not explicitly assigned to in the input line. This avoids running `stty` at every external command by accidentally exporting it. Also note that `STTY` should not be used for window size specifications; these will not be local to the command.
`TIMEFMT`
  The format of process time reports with the `time` keyword. The default is ``%E real %U user %S system %P %J'`. Recognizes the following escape sequences:
  `%`
    A `%`.
  `%U`
    CPU seconds spent in user mode.
  `%S`
    CPU seconds spent in kernel mode.
  `%E`
    Elapsed time in seconds.
  `%P`
    The CPU percentage, computed as (%U+%S)/%E.
  `%J`
    The name of this job.
  A star may be inserted between the percent sign and flags printing time. This cause the time to be printed in `hh:mm:ss.ttt` format (hours and minutes are only printed if they are not zero).
`TMOUT`
  If this parameter is nonzero, the shell will receive an `ALRM` signal if a command is not entered within the specified number of seconds after issuing a prompt. If there is a trap on `SIGALRM`, it will be executed and a new alarm is scheduled using the value of the `TMOUT` parameter after executing the trap. If no trap is set, and the idle time of the terminal is not less than the value of the `TMOUT` parameter, zsh terminates. Otherwise a new alarm is scheduled to `TMOUT` seconds after the last keypress.
`TMPPREFIX`
  A pathname prefix which the shell will use for all temporary files. Note that this should include an initial part for the file name as well as any directory names. The default is ``/tmp/zsh'`.
`watch (WATCH)`
  An array (colon-separated list) of login/logout events to report. If it contains the single word ``all'`, then all login/logout events are reported. If it contains the single word ``notme'`, then all login/logout events are reported except for those originating from `$USERNAME`. An entry in this list may consist of a username, an `@` followed by a remote hostname, and a `%` followed by a line (tty). Any or all of these components may be present in an entry; if a login/logout event matches all of them, it is reported.
`WATCHFMT`
  The format of login/logout reports if the `watch` parameter is set. Default is ``%n has %a %l from %m'`. Recognizes the following escape sequences:
  `%n`
    The name of the user that logged in/out.
  `%a`
    The observed action, i.e. ``logged on'` or ``logged off'`.
  `%l`
    The line (tty) the user is logged in on.
  `%M`
    The full hostname of the remote host.
  `%m`
    The hostname up to the first ``.'`. If only the IP address is available or the utmp field contains the name of an X-windows display, the whole name is printed. NOTE: The `%m` and `%M` escapes will work only if there is a host name field in the `utmp` on your machine. Otherwise they are treated as ordinary strings.
  `%S (%s)`
    Start (stop) standout mode.
  `%U (%u)`
    Start (stop) underline mode.
  `%B (%b)`
    Start (stop) boldface mode.
  `%t`
  `%@`
    The time, in 12-hour, am/pm format.
  `%T`
    The time, in 24-hour format.
  `%w`
    The date in day-dd format.
  `%W`
    The date in mm/dd/yy format.
  `%D`
    The date in yy-mm-dd format.
  `%(x:true-text:false-text)`
    Specifies a ternary expression. The character following the `x` is arbitrary; the same character is used to separate the text for the true result from that for the false result. Both the separator and the right parenthesis may be escaped with a backslash. Ternary expressions may be nested. The test character `x` may be any one of `l`, `n`, `m`, or `M`, which indicate a true result if the corresponding escape sequence would return a non-empty value; or it may be `a`, which indicates a true result if the watched user has logged in, or false if he has logged out. Other characters evaluate to neither true nor false; the entire expression is omitted in this case. If the result is true, then the true-text is formatted according to the result above and printed, and the false-text is skipped. If false, the true-text is skipped, and the false-text is formatted and printed. Either or both of the branches may be empty, but both separators must always be present.
`WORDCHARS`
  A list of non-alphanumeric characters considered part of a word by the line editor.
`ZDOTDIR`
  The directory to search for shell startup files (``.zshrc'`, etc), if not `$HOME`.

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