Bash prompt with the last exit code

I've been trying to customize my Bash prompt so that it will look like

[feralin@localhost ~]$ _

with colors. I managed to get constant colors (the same colors every time I see the prompt), but I want the username ('feralin') to appear red, instead of green, if the last command had a nonzero exit status. I came up with:

\e[1;33m[$(if [[ $? == 0  ]]; then echo "\e[0;31m"; else echo "\e[0;32m"; fi)\u\e[m@\e[1;34m\h \e[0;35m\W\e[1;33m]$ \e[m

However, from my observations, the $(if ...; fi) seems to be evaluated once, when the .bashrc is run, and the result is substituted forever after. This makes the name always green, even if the last exit code is nonzero (as in, echo $?). Is this what is happening? Or is it simply something else wrong with my prompt? Long question short, how do I get my prompt to use the last exit code?

As you are starting to border on a complex PS1, you might consider using PROMPT_COMMAND. With this, you set it to a function, and it will be run after each command to generate the prompt.

You could try the following in your ~/.bashrc file:

PROMPT_COMMAND=__prompt_command    # Function to generate PS1 after CMDs

__prompt_command() {
    local EXIT="$?"                # This needs to be first
    PS1=""

    local RCol='\[\e[0m\]'

    local Red='\[\e[0;31m\]'
    local Gre='\[\e[0;32m\]'
    local BYel='\[\e[1;33m\]'
    local BBlu='\[\e[1;34m\]'
    local Pur='\[\e[0;35m\]'

    if [ $EXIT != 0 ]; then
        PS1+="${Red}\u${RCol}"        # Add red if exit code non 0
    else
        PS1+="${Gre}\u${RCol}"
    fi

    PS1+="${RCol}@${BBlu}\h ${Pur}\W${BYel}$ ${RCol}"
}

This should do what it sounds like you want. Take a look a my bashrc's sub file if you want to see all the things I do with my __prompt_command function.

If you don't want to use the prompt command there are two things you need to take into account:

1. getting the value of $? before anything else. Otherwise it'll be overridden.
2. escaping all the $'s in the PS1 (so it's not evaluated when you assign it)

Working example using a variable

PS1="\$(VALU="\$?" ; echo \$VALU ; date ; if [ \$VALU == 0 ]; then echo zero; else echo nonzero; fi) "

Working example without a variable

Here the if needs to be the first thing, before any command that would override the $?.

PS1="\$(if [ \$? == 0 ]; then echo zero; else echo nonzero; fi) "

Notice how the \$() is escaped so it's not executed right away, but each time PS1 is used. Also all the uses of \$?.

I wanted to keep default Debian colors, print the exact code, and only print it on failure:

# Show exit status on failure.
PROMPT_COMMAND=__prompt_command

__prompt_command() {
    local curr_exit="$?"

    local BRed='\[\e[0;91m\]'
    local RCol='\[\e[0m\]'

    PS1='${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '

    if [ "$curr_exit" != 0 ]; then
        PS1="[${BRed}$curr_exit${RCol}]$PS1"
    fi
}

Compact solution:

PS1='... $(code=${?##0};echo ${code:+[error: ${code}]})'

This approach does not require PROMPT_COMMAND (apparently this can be slower sometimes) and prints [error: <code>] if the exit code is non-zero, and nothing if it's zero:

... > false
... [error: 1]> true
... >

Change the [error: ${code}] part depending on your liking, with ${code} being the non-zero code to print.

Note the use of ' to ensure the inline $() shell gets executed when PS1 is evaluated later, not when the shell is started.

As bonus, you can make it colorful in red by adding \e[01;31m in front and \e[00m after to reset:

PS1='... \e[01;31m$(code=${?##0};echo ${code:+[error: ${code}]})\e[00m'

--

How it works:

• it uses bash parameter substitution
• first, the ${?##0} will read the exit code $? of the previous command
• the ## will remove any 0 pattern from the beginning, effectively making a 0 result an empty var (thanks @blaskovicz for the trick)
• we assign this to a temporary code variable as we need to do another substitution, and they can't be nested
• the ${code:+REPLACEMENT} will print the REPLACEMENT part only if the variable code is set (non-empty)
• this way we can add some text and brackets around it, and reference the variable again inline: [error: ${code}]

The following provides a leading green check mark when the exit code is zero and a red cross in all other cases. The remainder is a standard colorized prompt. The printf statements can be modified to present the two states that were originally requested.

PS1='$(if [ $? -eq 0 ]; then printf "\033[01;32m""\xE2\x9C\x93"; else printf "\033[01;31m""\xE2\x9C\x95"; fi) \[\e[00;32m\]\u@\h\[\e[00;30m\]:\[\e[01;33m\]\w\[\e[01;37m\]\$ '

Why didn't I think about that myself? I found this very interesting and added this feature to my 'info-bar' project. Eyes will turn red if the last command failed.

#!/bin/bash
eyes=(O o ∘ ◦ ⍤ ⍥) en=${#eyes[@]} mouth='_'
face () { # gen random face
    [[ $error -gt 0 ]] && ecolor=$RED || ecolor=$YLW
    if [[ $1 ]]; then printf "${eyes[$[RANDOM%en]]}$mouth${eyes[$[RANDOM%en]]}"
                 else printf "$ecolor${eyes[$[RANDOM%en]]}$YLW$mouth$ecolor${eyes[$[RANDOM%en]]}$DEF"
    fi
}
info () { error=$?
    [[ -d .git ]] && {  # If in git project folder add git status to info bar output
        git_clr=('GIT' $(git -c color.ui=always status -sb)) # Colored output 4 info
        git_tst=('GIT' $(git                    status -sb)) # Simple  output 4 test
    }
    printf -v line "%${COLUMNS}s"                            # Set border length
    date=$(printf "%(%a %d %b %T)T")                         # Date & time 4 test
    test=" O_o $PWD  ${git_tst[*]} $date o_O "               # Test string
    step=$[$COLUMNS-${#test}]; [[ $step -lt 0 ]] && step=0   # Count spaces
    line="$GRN${line// /-}$DEF\n"                            # Create lines
    home="$BLD$BLU$PWD$DEF"                                  # Home dir info
    date="$DIM$date$DEF"                                     # Colored date & time
           #------+-----+-------+--------+-------------+-----+-------+--------+
           # Line | O_o |homedir| Spaces | Git  status | Date|  o_O  |  Line  |
           #------+-----+-------+--------+-------------+-----+-------+--------+
    printf "$line $(face) $home %${step}s ${git_clr[*]} $date $(face) \n$line" # Final info string
}
PS1='${debian_chroot:+($debian_chroot)}\n$(info)\n$ '
case "$TERM" in xterm*|rxvt*)
    PS1="\[\e]0;${debian_chroot:+($debian_chroot)} $(face 1) \w\a\]$PS1";;
esac

Improved demure answer:

I think this is important because the exit status is not always 0 or 1.

if [ $EXIT != 0 ]; then
    PS1+="${Red}${EXIT}:\u${RCol}"      # Add red if exit code != 0
else
    PS1+="${Gre}${EXIT}:\u${RCol}"      # Also displays exit status
fi

To preserve the original prompt format (not just colors), you could append following to the end of file ~/.bashrc:

PS1_ORIG=$PS1 # original primary prompt value
PROMPT_COMMAND=__update_prompt # Function to be re-evaluated after each command is executed
__update_prompt() {
    local PREVIOUS_EXIT_CODE="$?"
    if [ $PREVIOUS_EXIT_CODE != 0 ]; then
        local RedCol='\[\e[0;31m\]'
        local ResetCol='\[\e[0m\]'
        local replacement="${RedCol}\u${ResetCol}"
	
        # Replace username color
        PS1=${PS1_ORIG//]\\u/]$replacement}
        ## Alternative: keep same colors, append exit code
        #PS1="$PS1_ORIG[${RedCol}error=$PREVIOUS_EXIT_CODE${ResetCol}]$ "
    else
        PS1=$PS1_ORIG
    fi
}

See also the comment about the alternative approach that preserves username color and just appends an error code in red to the end of the original prompt format.

You can achieve a similar result to include a colored (non-zero) exit code in a prompt, without using subshells in the prompt nor prompt_command.

You color the exit code portion of the prompt, while having it only appear when non-zero.

Core 2$ section of the prompt: \\[\\033[0;31;4m\\]\${?#0}\\[\\033[0;33m\\]\$ \\[\\033[0m\\]

Key elements:

• return code, if not 0: \${?#0} (specificly "removes prefix of 0")
• change color without adding to calculated prompt-width: \\[\\033[0;31m\\]
  • \\[ - begin block
  • \\033 - treat as 0-width, in readline calculations for cmdline editing
  • [0;31;4m - escape code, change color, red fg, underline
  • \\] - end block

Components:

• \\[\\033[0;31;4m\\] - set color 0;31m fg red, underline
• \${?#0} - display non-zero status (by removing 0 prefix)
• \\[\\033[0;33m\\] - set color 0;33m fg yellow
• \$ - $ or # on EUID
• \\[\\033[0m\\] - reset color

The full PS1 I use (on one host):

declare -x PS1="\\[\\033[0;35m\\]\\h\\[\\033[1;37m\\] \\[\\033[0;37m\\]\\w \\[\\033[0;33m\\]\\[\\033[0;31;4m\\]\${?#0}\\[\\033[0;33m\\]\$ \\[\\033[0m\\]"

Note: this addresses a natural extension to this question, in a more enduring way then a comment.