code / scripts

   1 #!/bin/sh
   2 # Simple shell script to parse one command line argument at a time.
   3 #
   4 #   Usage: arg <flag> args...
   5 #
   6 # If the flag is present among the given arguments, its value (if any) will be printed.
   7 # Otherwise, the command will fail (subject to the special values below).
   8 # Positional arguments are those that either don't begin with a '-', or appear
   9 # after a lone "--" argument.
  10 #
  11 #   Special Values:
  12 #     @                 Print all positional arguments (i.e. excluding flags).
  13 #     <num>             Print the Nth positional arg, if present, otherwise fail.
  14 #     <flag>?           Pipe output to /dev/null, but still use success status
  15 #                       to indicate if flag is present.
  16 #     <flag>=<default>  If flag is not present, use <default> as the value.
  17 #                       Always succeeds.
  18 #     <flag1>|<flag2>   If flag1 is not present, check flag2 instead.
  19 #
  20 #   Examples:
  21 #     arg '-v|--verbose?' "$@" && verbose=yes || verbose=no
  22 #     if logfile="$(arg --log "$@")"; then ...; fi
  23 #     path="$(arg '-p|--path=/tmp/default' "$@")"
  24 #     for f in $(arg @ "$@"); do ...; done
  25 #     case "$(arg 1 "$@")" in ... esac
  26 #     arg verboten.txt'?' "$@" && echo "You can't use that file!" && exit 1
  27 #
  28 # Note: space-separated flag/value pairs are not supported, e.g. `ls -I \*.txt`
  29 # or `ls --ignore \*.txt`. In these cases, please use the following call
  30 # syntax instead: `ls -I\*.txt` or `ls -I=\*.txt` and `ls --ignore=\*.txt`.
  31 # Supporting space-separated flag/value pairs would make positional argument
  32 # functionality impossible because there would be no way to know whether x or y
  33 # is the first positional arg in these examples: `arg 1 -f x y`, `arg 1 --foo x y`
  34 # (At least, not without telling `arg` whether or not each flag expects a value)
  35 #
  36 # Note 2: If you expect arguments to contain "\x1E", you may want to run `arg`
  37 # with a custom record separator in the environment variable `RS`. Or, if you want
  38 # to customize the output of `arg @ ...` to use a custom output record separator,
  39 # you can use the environment variable `ORS`.
  40 #
  41 [ $# -eq 0 ] && echo "arg: a single-flag argument parser. Usage: arg <flag> args..." && exit
  42 target="$1"; shift
  43 RS=${RS-$'\x1E'}
  44 ORS=${ORS-$'\n'}
  45 case "$target" in
  46     @) printf "%s$RS" "$@" | awk -v RS="$RS" -v ORS="$ORS" 'raw || !/^-/; /^--$/ {raw=1}' ;;
  47     --) ! printf "%s$RS" "$@" | awk -v RS="$RS" "/^--$/ {if (++count>1) exit 1}" ;;
  48     -[^-]\?) ! printf "%s$RS" "$@" | awk -v RS="$RS" "/^-[^-]*${target#-}/ {exit 1}" ;;
  49     *\?) $0 "${target%\?}" "$@" >/dev/null ;;
  50     *=*) default="${target#*=}"; $0 "${target%%=*}" "$@" || echo "$default" ;;
  51     *\|*) $0 "${target%%\|*}" "$@" || $0 "${target#*\|}" "$@" ;;
  52     [1-9]*) n="$target"; [ $# -ge "$n" ] && ORS="$RS" $0 @ "$@" | awk -v RS="$RS" "NR==$n" ;;
  53     -[^-]) ! printf "%s$RS" "$@" | awk -v RS="$RS" "
  54         /^--$/ {exit 0}
  55         /^-[^-]*${target#-}/ {sub(/^-[^-]*${target#-}=?/,\"\"); print; exit 1}" ;;
  56     *) ! printf "%s$RS" "$@" | awk -v RS="$RS" "
  57         /^--$/ {exit 0}
  58         /^$target$/ {exit 1}
  59         /^$target=/ {sub(/^$target=/,\"\"); print; exit 1}" ;;
  60 esac