Get stack trace in Bash shell script/program.

stack_trace.sh

# LICENSE: MIT, wtfpl or whatever OSS license you like
function get_stack () {
   STACK=""
   local i message="${1:-""}"
   local stack_size=${#FUNCNAME[@]}
   # to avoid noise we start with 1 to skip the get_stack function
   for (( i=1; i<$stack_size; i++ )); do
      local func="${FUNCNAME[$i]}"
      [ x$func = x ] && func=MAIN
      local linen="${BASH_LINENO[$(( i - 1 ))]}"
      local src="${BASH_SOURCE[$i]}"
      [ x"$src" = x ] && src=non_file_source

      STACK+=$'\n'"   at: "$func" "$src" "$linen
   done
   STACK="${message}${STACK}"
}

Here's a version that prints arguments, if shopt -s extdebug is in effect:

function stack_trace() {
    local -a stack=()
    local stack_size=${#FUNCNAME[@]}
    local -i start=${1:-1}
    local -i max_frames=${2:-$stack_size}
    ((max_frames > stack_size)) && max_frames=$stack_size
    local -i i
    local -i max_funcname=0
    local -i stack_size_len=${#max_frames}
    local -i max_filename_len=0
    local -i max_line_len=0

    # to avoid noise we start with 1 to skip the stack function
    for (( i = start; i < max_frames; i++ )); do
	local func="${FUNCNAME[$i]:-(top level)}"
	((${#func} > max_funcname)) && max_funcname=${#func}
	local src="${BASH_SOURCE[$i]:-(no file)}"
	# Line number is used as a string here, not an int,
	# since we want the length of it as a string.
	local line="${BASH_LINENO[$(( i - 1 ))]}"
	((${#src} > max_filename_len)) && max_filename_len=${#src}
	((${#line} > max_line_len)) && max_line_len=${#line}
    done
    local stack_frame_str="    (%${stack_size_len}d)   %${max_filename_len}s:%-${max_line_len}d  %${max_funcname}s%s"
    local -i arg_count=${BASH_ARGC[0]}
    for (( i = start; i < max_frames; i++ )); do
	local func="${FUNCNAME[$i]:-(top level)}"
	local -i line="${BASH_LINENO[$(( i - 1 ))]}"
	local src="${BASH_SOURCE[$i]:-(no file)}"
	local -i frame_arg_count=${BASH_ARGC[$i]}
	local argstr=
	if ((frame_arg_count > 0)) ; then
	    local -i j
	    for ((j = arg_count + frame_arg_count - 1; j >= arg_count; j--)) ; do
		argstr+=" ${BASH_ARGV[$j]}"
	    done
	fi
	# We need a dynamically generated string to get the columns correct.
	# shellcheck disable=SC2059
	stack+=("$(printf "$stack_frame_str" "$((i - start))" "$src" "$line" "$func" "${argstr:+ $argstr}")")
	arg_count=$((arg_count + frame_arg_count))
    done
    (IFS=$'\n'; echo "${stack[*]}")
}

I'm impressed with all improvements I see here. Perhaps somebody would submit their version as an improvement to https://github.com/olivergondza/bash-strict-mode/

P.S. when printing stack traces, it's better to use STDERR

I did it that way so that higher level code can more conveniently capture the output; it can also redirect it to stderr. Either way works, certainly.

I find the arguments to be invaluable for debugging. I have a very complex script that itself provides an API, and there's a lot of control flow complexity. Ideally it would be written in Go or something, but none of those languages provide the convenience of shell scripting for running other commands.