CODEWITHSUNDEEP
gitbash
coredumperror
coredumperror

Reputation: 9100

Is it possible to pre-evaluate a value in bash's PS1?

I'm trying to build a Bash prompt which will have both my git branch information (using __git_ps1 from git's bash-completion) and a little colored smiley to indicate whether the most recently run command was successful.

The smiley is created using this technique, which I found here on SO:

SMILEY="${GREEN}:)${COLOR_NONE}"
FROWNY="${RED}:(${COLOR_NONE}"
STATUS_EMOTICON="if [ \$? = 0 ]; then echo \"${SMILEY}\"; else echo \"${FROWNY}\"; fi"

Here's the prompt line I want to use:

export PS1="[\t]${RED}[\u@$MACHINE:${BOLD_CYAN}\w${GREEN}\$(__git_ps1 ' %s')${RED}]${COLOR_NONE} \`${STATUS_EMOTICON}\`\n$ "

Unfortunately, it looks like the programs that are run by __git_ps1 override the $? value, and I end up with every emoticon being a green smiley, even after running false.

Taking out the __git_ps1 call...

export PS1="[\t]${RED}[\u@$MACHINE:${BOLD_CYAN}\w${RED}]${COLOR_NONE} \`${STATUS_EMOTICON}\`\n$ "

...makes the emoticon work correctly.

So what I apparently need to do is evaluate ${STATUS_EMOTICON} before running __git_ps1, but include the evaluated value after __git_ps1's output. Is that possible?

Upvotes: 4

Views: 622

Answers (1)

pynexj
pynexj

Reputation: 20688

Don't put $(cmd) or `cmd` directly in your PS1. Instead, use Bash's PROMPT_COMMAND var. What I usually do is define a function _PS1_cmd and set PROMPT_COMMAND=_PS1_cmd. Then in _PS1_cmd, I set misc vars I'd like to include in PS1. For example:

THE-OLD-PROMPT # cat prompt.rc
function _PS1_cmd()
{
    local saveExit=$?

    # This non-zero exit will not affect $? on command line
    g_git_ps1=$( echo TESTING; exit 1 )
    if (( saveExit )); then
        g_smiley=':('
    else
        g_smiley=':)'
    fi

    # Seems like this is not necessary, at least with bash 4.2.37. But
    # to be safe, always return it.
    return $saveExit
}

PROMPT_COMMAND=_PS1_cmd
PS1='$g_git_ps1 $g_smiley '
THE-OLD-PROMPT # source ./prompt.rc
TESTING :) ( exit 123 )
TESTING :( echo $?
123
TESTING :) echo $?
0
TESTING :)

Upvotes: 7

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