zsh: 13. Prompt Expansion

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# 13. Prompt Expansion

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## 13.1 Expansion of Prompt Sequences

Prompt sequences undergo a special form of expansion. This type of expansion is also available using the `-P` option to the `print` builtin.

If the `PROMPT_SUBST` option is set, the prompt string is first subjected to parameter expansion, command substitution and arithmetic expansion. See Expansion.

Certain escape sequences may be recognised in the prompt string.

If the `PROMPT_BANG` option is set, a ``!`' in the prompt is replaced by the current history event number. A literal ``!`' may then be represented as ``!!`'.

If the `PROMPT_PERCENT` option is set, certain escape sequences that start with ``%`' are expanded. Many escapes are followed by a single character, although some of these take an optional integer argument that should appear between the ``%`' and the next character of the sequence. More complicated escape sequences are available to provide conditional expansion.

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## 13.2 Simple Prompt Escapes

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### 13.2.1 Special characters

`%%`

  A ``%`'.

`%)`

  A ``)`'.

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### 13.2.2 Login information

`%l`

  The line (tty) the user is logged in on, without ``/dev/`' prefix. If the name starts with ``/dev/tty`', that prefix is stripped.

`%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. With a negative integer, trailing components of the hostname are shown.

`%n`

  `$USERNAME`.

`%y`

  The line (tty) the user is logged in on, without ``/dev/`' prefix. This does not treat ``/dev/tty`' names specially.

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### 13.2.3 Shell state

`%#`

  A ``#`' if the shell is running with privileges, a ``%`' if not. Equivalent to ``%(!.#.%%)`'. The definition of `privileged', for these purposes, is that either the effective user ID is zero, or, if POSIX.1e capabilities are supported, that at least one capability is raised in either the Effective or Inheritable capability vectors.

`%?`

  The return status 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 negative or no integer means print as many as there are. This is most useful in prompts `PS2` for continuation lines and `PS4` for debugging with the `XTRACE` option; in the latter case it will also work non-interactively.

`%d`
`%/`

  Present working directory (`$PWD`). If an integer follows the ``%`', it specifies a number of trailing components of `$PWD` to show; zero means the whole path. A negative integer specifies leading components, i.e. `%-1d` specifies the first component.

`%~`

  As `%d` and `%/`, but if `$PWD` has a named directory as its prefix, that part is replaced by a ``~`' followed by the name of the directory. If it starts with `$HOME`, that part is replaced by a ``~`'.

`%h`
`%!`

  Current history event number.

`%i`

  The line number currently being executed in the script, sourced file, or shell function given by `%N`. This is most useful for debugging as part of `$PS4`.

`%j`

  The number of jobs.

`%L`

  The current value of `$SHLVL`.

`%N`

  The name of the script, sourced file, or shell function that zsh is currently executing, whichever was started most recently. If there is none, this is equivalent to the parameter `$0`. An integer may follow the ``%`' to specify a number of trailing path components to show; zero means the full path. A negative integer specifies leading components.

`%c`
`%.`
`%C`

  Trailing component of `$PWD`. An integer may follow the ``%`' to get more than one component. Unless ``%C`' is used, tilde contraction is performed first. These are deprecated as `%c` and `%C` are equivalent to `%1~` and `%1/`, respectively, while explicit positive integers have the same effect as for the latter two sequences.

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### 13.2.4 Date and time

`%D`

  The date in yy`-`mm`-`dd format.

`%T`

  Current time of day, in 24-hour format.

`%t`
`%@`

  Current time of day, in 12-hour, am/pm format.

`%*`

  Current time of day in 24-hour format, with seconds.

`%w`

  The date in day`-`dd format.

`%W`

  The date in mm`/`dd`/`yy format.

`%D{`string`}`

  string is formatted using the `strftime` function. See man page strftime(3) for more details. Three additional codes are available: `%f` prints the day of the month, like `%e` but without any preceding space if the day is a single digit, and `%K`/`%L` correspond to `%k`/`%l` for the hour of the day (24/12 hour clock) in the same way.

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### 13.2.5 Visual effects

`%B` (`%b`)

  Start (stop) boldface mode.

`%E`

  Clear to end of line.

`%U` (`%u`)

  Start (stop) underline mode.

`%S` (`%s`)

  Start (stop) standout mode.

`%{`...`%}`

  Include a string as a literal escape sequence. The string within the braces should not change the cursor position. Brace pairs can nest.

  A positive numeric argument between the `%` and the %%({) is treated as described for `%G` below.

`%G`

  Within a `%{`...`%}` sequence, include a `glitch': that is, assume that a single character width will be output. This is useful when outputting characters that otherwise cannot be correctly handled by the shell, such as the alternate character set on some terminals. The characters in question can be included within a `%{`...`%}` sequence together with the appropriate number of `%G` sequences to indicate the correct width. An integer between the ``%`' and ``G`' indicates a character width other than one. Hence `%{`seq`%2G%}` outputs seq and assumes it takes up the width of two standard characters.

  Multiple uses of `%G` accumulate in the obvious fashion; the position of the `%G` is unimportant. Negative integers are not handled.

  Note that when prompt truncation is in use it is advisable to divide up output into single characters within each `%{`...`%}` group so that the correct truncation point can be found.

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## 13.3 Conditional Substrings in Prompts

`%v`

  The value of the first element of the `psvar` array parameter. Following the ``%`' with an integer gives that element of the array. Negative integers count from the end of the array.

`%(`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. This separator may not appear in the true-text, except as part of a %-escape sequence. A ``)`' may appear in the false-text as ``%)`'. true-text and false-text may both 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. A negative integer will be multiplied by -1. The test character x may be any of the following:

  `!`

    True if the shell is running with privileges.

  `#`

    True if the effective uid of the current process is n.

  `?`

    True if the exit status of the last command was n.

  `_`

    True if at least n shell constructs were started.

  `C`
  `/`

    True if the current absolute path has at least n elements relative to the root directory, hence `/` is counted as 0 elements.

  `c`
  `.`
  `~`

    True if the current path, with prefix replacement, has at least n elements relative to the root directory, hence `/` is counted as 0 elements.

  `D`

    True if the month is equal to n (January = 0).

  `d`

    True if the day of the month is equal to n.

  `g`

    True if the effective gid of the current process is n.

  `j`

    True if the number of jobs is at least n.

  `L`

    True if the `SHLVL` parameter is at least n.

  `l`

    True if at least n characters have already been printed on the current line.

  `S`

    True if the `SECONDS` parameter is at least n.

  `T`

    True if the time in hours is equal to n.

  `t`

    True if the time in minutes is equal to n.

  `v`

    True if the array `psvar` has at least n elements.

  `w`

    True if the day of the week is equal to n (Sunday = 0).

`%<`string`<`
`%>`string`>`
`%[`xstring`]`

  Specifies truncation behaviour for the remainder of the prompt string. The third, deprecated, 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. The string will be displayed in place of the truncated portion of any string; note this does not undergo prompt expansion.

  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`'. In this string, the terminating character (``<`', ``>`' or ``]`'), or in fact any character, may be quoted by a preceding ``\`'; note when using `print -P`, however, that this must be doubled as the string is also subject to standard `print` processing, in addition to any backslashes removed by a double quoted string: the worst case is therefore ``print -P "%<\\\\<<..."`'.

  If the string is longer than the specified truncation length, it will appear in full, completely replacing the truncated string.

  The part of the prompt string to be truncated runs to the end of the string, or to the end of the next enclosing group of the ``%(`' construct, or to the next truncation encountered at the same grouping level (i.e. truncations inside a ``%(`' are separate), which ever comes first. In particular, a truncation with argument zero (e.g. ``%<<`') marks the end of the range of the string to be truncated while turning off truncation from there on. For example, the prompt '%10<...<%~%<<%# ' will print a truncated representation of the current directory, followed by a ``%`' or ``#`', followed by a space. Without the ``%<<`', those two characters would be included in the string to be truncated.

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This document was generated by Peter Stephenson on April, 2 2008 using texi2html 1.78.