Explanation:
trap command signals executes command when one of signals is "raised".
history | tail -1l | cut -c -5$(command) outputs, executes the command and captures its output.
When command fails, this snippet of code captures history number of last command savedlast command saved into history, and stores it in variable for future deletion.
(Note: if command which failed is not saved into history due to HISTCONTROL, HISTIGNORE, etc., you get history number of previous command, marking it for deletion.)
Enclosing command in inSimple, but works incorrectly with $()HISTCONTROL, like and $(command)HISTIGNORE, executes – when command is not saved into history due to one of the variables, history number of last command saved into history is previous command's one; so, if incorrect command and captures its outputis not saved into history, previous command is going to be deleted.
Captured output is then prepended (not appended!) into FAILED_COMMANDS variable.Slightly more complicated version, which works correctly in that case:
debug_handler() {
LAST_COMMAND=$BASH_COMMAND;
}
error_handler() {
local LAST_HISTORY_ENTRY=$(history | tail -1l)
# if last command is in history (HISTCONTROL, HISTIGNORE)...
if [ "$LAST_COMMAND" == "$(cut -d ' ' -f 2- <<< $LAST_HISTORY_ENTRY)" ]
then
# ...prepend it's history number into FAILED_COMMANDS,
# marking the command for deletion.
FAILED_COMMANDS="$(cut -d ' ' -f 1 <<< $LAST_HISTORY_ENTRY) $FAILED_COMMANDS"
fi
}
trap error_handler ERR
trap debug_handler DEBUG
Because of that, when using this code, you cannot manually call history -d <n>
where n is smaller or equal to greatest number stored in FAILED_COMMANDS
and expect the code to work properly.
It's probably good idea to hook itexit_handler at EXIT, but you can also call it anytime earlier.