Customizing your shell prompt : tcsh and zsh shells
Shell prompts are extremely customizable. You can customize them in two ways: (1) by using command characters that print out special things and (2) by using colors. Also, customizing the prompt is different in different shells; I'm going to cover tcsh and zsh here. bash is the other popular shell, but I think it sucks, and I never use it, so I'm not going to waste any time on it.
tcsh
I'll start with tcsh, since it's the default BSD and Mac OS X shell. Here's a very simple prompt:
hostname%
That prompt is created with the following command:
setenv PROMPT '%m%# '
The %m is called a formatting sequence, and it is expanded to the hostname of your computer when tcsh outputs your prompt. Similarly, %# equals '>' (or the first character of the promptchars shell variable) if you're a normal user, or '#' (or the second character of promptchars) if you're root. Any letter with a % before it will be treated as a formatting sequence, so if you want to print a % sign, use %%. (Quick side note: you want the extra space at the end, or else the input will be squashed up against the prompt, and it's ugly and hard to read.) A popular prompt is the following:
Formatted:
[user@hostname:/current/path]%
Code
[%n@%m:%c]%#
%n is the username and %c is the current path. Instead of going through millions of examples illustrating all the different kinds of prompts you can have, I'm just going to include the complete list of formatting sequences from the tcsh(1) manpage:
%/ The current working directory.
%~ The current working directory, but with one's
home directory represented by `~' and other
users' home directories represented by `~user'
as per Filename substitution. `~user' substi-
tution happens only if the shell has already
used `~user' in a pathname in the current ses-
sion.
%c[[0]n], %.[[0]n]
The trailing component of the current working
directory, or n trailing components if a digit
n is given. If n begins with `0', the number
of skipped components precede the trailing
component(s) in the format `/<skipped>trail-
ing'. If the ellipsis shell variable is set,
skipped components are represented by an
ellipsis so the whole becomes `...trailing'.
`~' substitution is done as in `%~' above, but
the `~' component is ignored when counting
trailing components.
%C Like %c, but without `~' substitution.
%h, %!, !
The current history event number.
%M The full hostname (e.g. jaguar.apple.com).
%m The hostname up to the first `.' (e.g. jaguar).
%S (%s)
Start (stop) standout (reverse) mode.
%B (%b)
Start (stop) boldfacing mode.
%U (%u)
Start (stop) underline mode.
%t, %@
The time of day in 12-hour AM/PM format.
%T Like `%t', but in 24-hour format (but see the
ampm shell variable).
%p The `precise' time of day in 12-hour AM/PM
format, with seconds.
%P Like `%p', but in 24-hour format (but see the
ampm shell variable).
c c is parsed as in bindkey.
^c c is parsed as in bindkey.
%% A single `%'.
%n The user name.
%d The weekday in `Day' format.
%D The day in `dd' format.
%w The month in `Mon' format.
%W The month in `mm' format.
%y The year in `yy' format.
%Y The year in `yyyy' format.
%l The shell's tty.
%L Clears from the end of the prompt to end of
the display or the end of the line.
%$ Expands the shell or environment variable name
immediately after the `$'.
%# `>' (or the first character of the promptchars
shell variable) for normal users, `#' (or the
second character of promptchars) for the supe-
ruser.
%{string%}
Includes string as a literal escape sequence.
It should be used only to change terminal
attributes and should not move the cursor
location. This cannot be the last sequence in
prompt.
%? The return code of the command executed just
before the prompt.
%R In prompt2, the status of the parser. In
prompt3, the corrected string. In history,
the history string.
Next, on to color. This directly builds on the previous section by adding color escape sequences to the formatting sequences you can use. The following code colors the hostname red:
%{033[31m%}%m%{033[0m%}
The '31' and the %m have been bolded above because those are the only things you change. The 31 is the color code, and the %m is obviously where you put whatever you want to color. The rest of it is the same for every color coding; the beginning starts coloring, and the stuff afterwards stops coloring ('0' switches it back to default text color). You can use the following color codes:
30 - black
31 - red
32 - green
33 - yellow
34 - blue
35 - magenta
36 - cyan
37 - white
Not quite the same as a full Photoshop palette, but you can make a pretty nice prompt with it. Also, you can modify it further by including another control char:
%{033[1;31m%}%m%{033[0m%}
In this case, the '1' will make the following color bold. You can use the following modifiers:
0 - normal
1 - bold
2 - normal again
3 - background color
4 - underline the text
5 - blinking
You can also specify both a foreground and a background color. Use the following syntax to get (fairly hideous looking) Christmas colors:
%{033[2;41;32m%}%m%{033[0m%}
The '41' is the background color, and the '31' is the foreground color. The background color codes are the same as the foreground color codes, except they're 40-47 instead of 30-37.
Finally, you can also have a right-justified prompt. This is stored in the RPROMPT variable, and formatted in exactly the same way as PROMPT. People often like putting the time (%p) in RPROMPT.
zsh
zsh is customized in an extremely similar way. You still use formatting sequences, although some of them are a little different. The color codes are the same, although the color escape sequence is a little different. Other than that, it's pretty easy to move back and forth between a zsh and a tcsh prompt. The formatting sequences are the following (from zshmisc(1)):
%% A `%'.
%) A `)'.
%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 compo-
nents, 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.
%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. With a negative integer,
trailing components of the hostname are shown.
%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 sec-
onds.
%n $USERNAME.
%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.
%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.
%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. 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 without
/dev/ prefix. If name starts with /dev/tty this is
stripped.
%y The line (tty) the user is logged in on without
/dev/ prefix. It does not treat /dev/tty* spe-
cially.
%? 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 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-interac-
tively.
%E Clears to end of line.
%# A `#' if the shell is running with privileges, a
`%' if not. Equivalent to `%(!.#.%%)'. The defi-
nition 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. Negative integers count
from the end of the array.
%{...%}
Include a string as a literal escape sequence. The
string within the braces should not change the cur-
sor position. Brace pairs can nest.
%(x.true-text.false-text)
Specifies a ternary expression. The character fol-
lowing 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:
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 at least n characters have already
been printed on the current line.
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 ele-
ments.
_ True if at least n shell constructs were
started.
! True if the shell is running with privi-
leges.
%<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 stan-
dard print processing, in addition to any back-
slashes removed by a double quoted string: the
worst case is therefore `print -P "%<\\<<..."'.
If the string is longer than the specified trunca-
tion 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 sepa-
rate), 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.
%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.
As you can likely tell, zsh has some absurdly powerful prompt characters, but reasonably simple prompts are extremely similar to their tcsh counterparts:
tcsh:
[%n@%m:%c]%#
zsh:
[%n@%m:%/]%#
Not such a huge difference. The color sequence is slightly different, so use this kind of formatting:
%{e[0;31m%}%m%{e[0m%}
Again, the bold parts are the parts you edit. Also, you can customize RPROMPT in the same way.
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