argecho

#!/bin/sh -eu
# argecho (part of ossobv/vcutil) // wdoekes/2020 // Public Domain
#
# Quick and dirty argument echo. Helps when developing shell scripts, or
# when explaining shell quoting.
#
# Example situation:
#
#   curl='curl https://somewhere/api'
#   key=error_count
#   $curl -H 'Accept: application/json' | jq '.["'$key'"]'
#
# In the above example, it may be hard to tell where the single and
# double quotes should go.
#
# If you (backslash) escape the pipe between 'curl' and 'jq' and prepend
# the statement with 'argecho', you get this:
#
#   argecho $curl -H 'Accept: application/json' \| jq '.["'$key'"]'
#
# That outputs:
#
#   # nArgs: 7
#   # Warning: unescaped a pipe. Please remove escape when done with argecho.
#   'curl' 'https://somewhere/api' '-H' 'Accept: application/json' |
#     'jq' '.["error_count"]'
#
# And that output is safe to paste in your shell directly, so you can
# test if it works as expected.
#
# (Be sure to remove the backslash before the pipe when removing argecho.)

quoted() {
    # Stupid but effective shell quoting.
    # - Surround arguments with single quotes '...'.
    # - Escape single quotes by breaking out and adding backslash single quote.
    if test "$1" = "|"; then
        echo "# Warning: unescaped a pipe. \
Please remove escape when done with argecho." >&2
        printf '|\n '
    else
        printf '%s' "$1" | sed -e "s/'/'\\\\''/g;s/^/'/;s/$/'/"
    fi
}

echo "# nArgs: $#" >&2
if test $# -gt 0; then
    (
        printf '%s' "$(quoted "$1")"
        shift
        for arg in "$@"; do
            printf '%s' " $(quoted "$arg")"
        done
        echo
    ) | tac | tac  # buffer all output, to avoid stderr on the same line
fi