trap 'caller 1' ERR
set -e
is-oil()
{
test -n "$OIL_VERSION"
}
set -E || is-oil
trap 'echo "$BASH_SOURCE:$LINENO: error: failure during early startup! Details unavailable."' ERR
magic_exitvalue=$(($(kill -l CONT)+128))
backtrace()
{
{
local status=$?
if [ "$status" -eq "$magic_exitvalue" ]
then
echo '(omit backtrace)'
exit "$magic_exitvalue"
fi
local max file line func argc argvi i j
echo
echo 'Panic! Something failed unexpectedly.' "(status $status)"
echo 'While executing' "$BASH_COMMAND"
echo
echo Backtrace:
echo
max=${#BASH_LINENO[@]}
let max-- # The top-most frame is "special".
argvi=${BASH_ARGC[0]}
for ((i=1;i<max;++i))
do
file=${BASH_SOURCE[i]}
line=${BASH_LINENO[i-1]}
func=${FUNCNAME[i]}
argc=${BASH_ARGC[i]}
printf '%s:%d: ... in %q' "$file" "$line" "$func"
# BASH_ARGV: ... bar foo ...
# argvi ^
# argvi+argc ^
for ((j=argc-1; j>=0; --j))
do
printf ' %q' ${BASH_ARGV[argvi+j]}
done
let argvi+=argc || true
printf '\n'
done
if true
then
file=${BASH_SOURCE[i]}
line=${BASH_LINENO[i-1]}
printf '%s:%d: ... at top level\n' "$file" "$line"
fi
} >&2
exit "$magic_exitvalue"
unreachable
}
shopt -s extdebug
trap 'backtrace' ERRThe Bash code is not only fast but pretty easy to understand (other than perhaps the header, which I never have to change).
There are some ways around this:
#!/bin/sh
[ "${DEBUG:-0}" = "1" ] && set -x
set -u
foo="$( my-external-program | pipe1 | pipe2 | pipe3 )"
if [ -z "$foo" ] ; then
echo "Error: I didn't get any output; exiting!"
exit 1
fi
echo "Well I got something back. Was it right?"
if ! printf "%s\n" "$foo" | grep -q -E 'some-extended-regex' ; then
echo "Error: '$foo' didn't match what I was looking for; exiting!"
exit 1
fi
echo "Do the thing now..."
Advanced diagnosis code won't make your program work better, but it will make it more complicated. Re-running with tracing enabled works just as well 99% of the time.
$ osh -c 'set -E; set -o |grep errtrace'
set -o errtrace
(The Oils runtime supports FUNCNAME BASH_SOURCE and all that, but there is room for a much better introspection API. It actually has a JSON crash report with a shell stack dump, but it probably needs some polish.)
What's the point? You can't fix them anyway
Here's an excerpt that shows how to set PS4 from a main() in a .env shell script for configuring devcontainer userspace:
for arg in "${@}"; do
case "$arg" in
--debug)
export __VERBOSE=1 ;
#export PS4='+${LINENO}: ' ;
#export PS4='+ #${BASH_SOURCE}:${LINENO}:${FUNCNAME[0]:+${FUNCNAME[0]}()}:$(date +%T)\n+ ' ;
#export PS4='+ ${LINENO} ${FUNCNAME[0]:+${FUNCNAME[0]}()}: ' ;
#export PS4='+ $(printf "%-4s" ${LINENO}) | '
export PS4='+ $(printf "%-4s %-24s " ${LINENO} ${FUNCNAME[0]:+${FUNCNAME[0]}} )| '
#export PS4='+ $(printf "%-4s %-${SHLVL}s %-24s" ${LINENO} " " ${FUNCNAME[0]:+${FUNCNAME[0]}} )| '
;;
--debug-color|--debug-colors)
export __VERBOSE=1 ;
# red=31
export ANSI_FG_BLACK='\e[30m'
#export MID_GRAY_256='\e[38;5;244m' # Example: a medium gray
export _CRESET='\e[0m'
export _COLOR="${ANSI_FG_BLACK}"
printf "${_COLOR}DEBUG: --debug-color: This text is ANSI gray${_CRESET}\n" >&2
export PS4='+ $(printf "${_COLOR}%-4s %-24s%s |${_CRESET} " ${LINENO} "${FUNCNAME[0]:+${FUNCNAME[0]}}" )'
;;
esac
done
function error_handler {
echo "Error occurred on line $(caller)" >&2
awk 'NR>L-4 && NR<L+4 { printf "%-5d%3s%s\n",NR,(NR==L?">>>":""),$0 }' L=$1 $0 >&2
}
if (echo "${SHELL}" | grep "bash"); then
trap 'error_handler $LINENO' ERR
fiAs an aside, I actually wonder if Bash's caller() was inspired by Perl's.
There is also Carp and friends, plus Data::Dumper when you not only need the stack trace but also the state of objects and data structures. Which is something that I don't think Bash can really do at all.
for value in "${SOMEARRAY[@]}"; do
echo "${value}"
done
for key in "${!SOMEARRAY[@]}"; do
echo "key: ${key} - value: ${SOMEARRAY["${key}"]}"
done
declare -p SOMEARRAY
declare -a SOMEARRAY=([0]="a" [1]="b" [2]="c" [3]="d" [4]="e" [5]="f")
Let's "dump" all variables that start with "BASH":
for k in "${!BASH@}"; do
declare -p "${k}"
done
for k in "${!BASH@}"; do
echo "${k}: ${!k}"
done
newAccount2025•9h ago
inetknght•9h ago
For what it's worth, I think `set -euo pipefail` should be default for every script, and thoroughly checked with shellcheck.net.
scns•8h ago
This
mananaysiempre•8h ago
(I rather dislike shellcheck because it combines genuine smells with opinions, such as insisting on $(...) instead of `...`. For the same reason, with Python I regularly use pyflakes but can’t stand flake8. But to each their own.)
koolba•5h ago
Only one of those can be (sanely) nested. Why would you ever want to use backticks?
oguz-ismail•4h ago
imcritic•8h ago
https://mywiki.wooledge.org/BashPitfalls#set_-euo_pipefail
larkost•7h ago
It is not that `set -e` is bad, it is that bash is a bit weird in this area and you have to know when things eat errors and when they don't. This is not really changed by `set -e`: you already had to know them to make safe code. `set -e` does not wave a magic wand saying you don't have to understand bash error control.
But having `set -e` is almost universally better for people who do not understand it (and I would argue also for people who do). Without it you are responsible for implementing error handling on almost every line.
As other have already said: this is one of those things that generally pushes me to other languages (in my case often Python), as the error handling is much more intuitive, and much less tricky to get right.
eikenberry•7h ago
koolba•9h ago
forrestthewoods•6h ago