Zsh prompt showing last error code only once - zsh

Question

I would like my prompt to show a cross (✘) when the previous command fails. I use the following code:
export PROMPT=$'%(?..✘\n)\n› '
This gives me the following output:
› echo Hello
Hello
› asjdfiasdf
zsh: command not found: asjdfiasdf
✘
›
✘
I would like to modify the prompt so that it does not repeat the cross when the prompt is redrawn after Enter (the third case in the example above).
Is it possible?

Answer 1

I think I got it. Let me know if you find a bug...
preexec() {
preexec_called=1
}
precmd() {
if [ "$?" != 0 ] && [ "$preexec_called" = 1 ]
then echo ✘; unset preexec_called; fi
}
PROMPT=$'\n› '
Result:
› ofaoisfsaoifoisafas
zsh: command not found: ofaoisfsaoifoisafas
✘
›
› echo $? # (not overwritten)
127

Answer 2

I do this in my zsh, though with colors rather than unicode characters. It's the same principle.
First, I set up my colors, ensuring that they are only used when they are supported:
case $TERM in
( rxvt* | vt100* | xterm* | linux | dtterm* | screen )
function PSC() { echo -n "%{\e[${*}m%}"; } # insert color-specifying chars
ERR="%(0?,`PSC '0;32'`,`PSC '1;31'`)" # if last cmd!=err, hash=green, else red
;;
( * )
function PSC() { true; } # no color support? no problem!
ERR=
;;
esac
Next, I set up a magic enter function (thanks to this post about an empty command (ignore the question, see how I adapt it here):
function magic-enter() { # from https://superuser.com/a/625663
if [[ -n $BUFFER ]]
then unset Z_EMPTY_CMD # Enter was pressed on an empty line
else Z_EMPTY_CMD=1 # The line was NOT empty when Enter was pressed
fi
zle accept-line # still perform the standard binding for Enter
}
zle -N magic-enter # define magic-enter as a widget
bindkey "^M" magic-enter # Backup: use ^J
Now it's time to interpret capture the command and use its return code to set the prompt color:
setopt prompt_subst # allow variable substitution
function preexec() { # just after cmd has been read, right before execution
Z_LAST_CMD="$1" # since $_ is unreliable in the prompt
#Z_LAST_CMD="${1[(wr)^(*=*|sudo|-*)]}" # avoid sudo prefix & options
Z_LAST_CMD_START="$(print -Pn '%D{%s.%.}')"
Z_LAST_CMD_START="${Z_LAST_CMD_START%.}" # zsh <= 5.1.1 makes %. a literal dot
Z_LAST_CMD_START="${Z_LAST_CMD_START%[%]}" # zsh <= 4.3.11 makes %. literal
}
function precmd() { # just before the prompt is rendered
local Z_LAST_RETVAL=$? # $? only works on the first line here
Z_PROMPT_EPOCH="$(print -Pn '%D{%s.%.}')" # nanoseconds, like date +%s.%N
Z_PROMPT_EPOCH="${Z_PROMPT_EPOCH%.}" # zsh <= 5.1.1 makes %. a literal dot
Z_PROMPT_EPOCH="${Z_PROMPT_EPOCH%[%]}" # zsh <= 4.3.11 makes %. a literal %.
if [ -n "$Z_LAST_CMD_START" ]; then
Z_LAST_CMD_ELAPSED="$(( $Z_PROMPT_EPOCH - $Z_LAST_CMD_START ))"
Z_LAST_CMD_ELAPSED="$(printf %.3f "$Z_LAST_CMD_ELAPSED")s"
else
Z_LAST_CMD_ELAPSED="unknown time"
fi
# full line for error if we JUST got one (not after hitting <enter>)
if [ -z "$Z_EMPTY_CMD" ] && [ $Z_LAST_RETVAL != 0 ]; then
N=$'\n' # set $N to a literal line break
LERR="$N$(PSC '1;0')[$(PSC '1;31')%D{%Y/%m/%d %T}$(PSC '1;0')]"
LERR="$LERR$(PSC '0;0') code $(PSC '1;31')$Z_LAST_RETVAL"
LERR="$LERR$(PSC '0;0') returned by last command"
LERR="$LERR (run in \$Z_LAST_CMD_ELAPSED):$N"
LERR="$LERR$(PSC '1;31')\$Z_LAST_CMD$(PSC '0;0')$N$N"
print -PR "$LERR"
fi
}
Finally, set the prompt:
PROMPT="$(PSC '0;33')[$(PSC '0;32')%n#%m$(PSC '0;33') %~$PR]$ERR%#$(PSC '0;0') "
Here's how it looks:
A more direct answer to the question, adapted from the above:
function magic-enter() { # from https://superuser.com/a/625663
if [[ -n $BUFFER ]]
then unset Z_EMPTY_CMD # Enter was pressed on an empty line
else Z_EMPTY_CMD=1 # The line was NOT empty when Enter was pressed
fi
zle accept-line # still perform the standard binding for Enter
}
zle -N magic-enter # define magic-enter as a widget
bindkey "^M" magic-enter # Backup: use ^J
function precmd() { # just before the prompt is rendered
local Z_LAST_RETVAL=$? # $? only works on the first line here
# full line for error if we JUST got one (not after hitting <enter>)
if [ -z "$Z_EMPTY_CMD" ] && [ $Z_LAST_RETVAL != 0 ]; then
echo '✘'
fi
}
PROMPT=$'\n› '
With screen shot:

Answer 3

Use the prexec and precmd hooks:
The preexec hook is called before any command executes. It isn't called when no command is executed. For example, if you press enter at an empty prompt, or a prompt that is only whitespace, it won't be called. A call to this hook signals that a command has been run.
The precmd hook is called before the prompt will be displayed to collect the next command. Before printing the prompt you can print out the exit status. In here we can check if a command was just executed, and if there's a status code we want to display.
This is very similar to the solution suggested by #sneep, which is also a great solution. It's worth using the hooks though so that if you've got anything else registering for these hooks they can do so too.
# print exit code once after last command output
function track-exec-command() {
zsh_exec_command=1
}
function print-exit-code() {
local -i code=$?
(( code == 0 )) && return
(( zsh_exec_command != 1 )) && return
unset zsh_exec_command
print -rC1 -- ''${(%):-"%F{160}✘ exit status $code%f"}''
}
autoload -Uz add-zsh-hook
add-zsh-hook preexec track-exec-command
add-zsh-hook precmd print-exit-code

Answer 4

Thanks to everyone for their answers. Four years later, I would like to illustrate a variation on sneep's answer for those looking for the error code and an alert without a symbol. This is a minimalist prompt but when an error occurs it displays the error code and > in red following the top level directory.
preexec() {
preexec_called=1
}
precmd() {
if [ "$?" != 0 ] && [ "$preexec_called" = 1 ]; then
unset preexec_called
PROMPT='%B%F{blue}%1~%f%b%F{red} $? > %F{black}'
else
PROMPT='%B%F{blue}%1~%f%b%F{blue} > %F{black}'
fi
}