Prompt Expansion

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 section 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. Some escapes take an optional integer argument, which 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 contraction is performed first.

%h

%!

Current history event number.

%L

The current value of $SHLVL.

%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 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.

%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 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.

%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. Brace pairs can nest.

%(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. 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.

!

True if the shell is running with privileges.

%<string<

%>string>

%[xstring]

Specifies truncation behaviour. 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. If this integer is zero, or missing, truncation is disabled. Truncation is initially disabled. The string will be displayed in place of the truncated portion of any string. 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 `\'. % escapes are not recognised. If the string is longer than the specified truncation length, it will appear in full, completely replacing the truncated string.

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