params

• shell parameter parsers

• pass parameters to another script

• Manual Case-Loop Parser

  • Bash Equals-Separated

  • with one or more values

  • additional params on --

  • shift with uncertain params

• POSIX getopts Parser

• GNU getopt Parser

• bash-argparse Library

• docopts

• argbash Code Generator

• shflags (Google-style shell option lib)

• references

[!TIP|label:see also:]

• * iMarslo: parameter substitution

shell parameter parsers

PARSER STYLE	DESCRIPTION	PROS	CONS	PORTABILITY
🔸 case + shift loop	Manual parsing with a while + case combo	- Highly customizable - Simple	- Error-prone for complex flags - No automatic help	✅ POSIX-compliant
🔸 getopts (built-in)	Built-in short-option parser	- Easy for short options (-x)	- No long options - No auto help	✅ POSIX-compliant
🔹 getopt (external)	External tool to parse long/short flags	- Supports long & short - Auto reordering	- Not always installed - Not portable across BSD/Linux	⚠️ Not portable
🔸 bash-argparse (lib)	Bash-based helper library	- Structured, powerful - Python-like syntax	- Adds dependency - Not always installed	❌ Bash-only
🔹 docopts (doc-style)	Parses from usage doc string	- Clean UX - Declarative	- Heavy - Requires Python or external	❌ External
🔸 argbash (codegen)	Generates parsing boilerplate	- Auto docs/help - Safe/robust	- Needs build step	❌ Not runtime native
🔹 shflags (Google)	Lightweight Bash lib	- Google-style - Nice syntax	- Needs sourcing a lib	⚠️ Bash-only

PARSER	SHORT OPTS	LONG OPTS	PORTABLE	HELP GEN	EXTERNAL?
Manual Case	✅	✅ (manual)	✅ POSIX	❌	❌
getopts	✅	❌	✅ POSIX	❌	❌
getopt	✅	✅	❌	❌	✅ (GNU)
bash-argparse	✅	✅	❌ Bash	✅	✅
docopts	✅	✅	❌	✅	✅ (Python)
argbash	✅	✅	❌	✅	✅ (tool)
shflags	✅	✅	❌	✅	✅ (lib)

pass parameters to another script

[!NOTE]

• objective:

  $ ./b.sh 1 2 3 4 5` -> $ ./a.sh 2 3 4 5

• b.sh

  #!/bin/bash
  echo """
  b.sh:
    \$1                   : "$1"
    \$#                   : "$#"
    \$@                   : "$@"
    \${@: -1}             : ${@: -1}
    \${@: -2}             : ${@: -2}
    \${@: -3}             : ${@: -2}
    \${@: -\$(( \$#-1 ))} : ${@: -$(( $#-1 ))}
    \$(echo '\${@: -\$(( \$#-1 ))}' | cut -d' ' -f1-) : $(echo "${@: -$(( $#-1 ))}" | cut -d' ' -f1-)
  """
  
  echo -e "\n'~~> ./a.sh \"\${@: -1}\"': ~~~> ./a.sh ${@: -1}:"
  ./a.sh "${@: -1}"
  
  echo -e "\n'~~> ./a.sh \$(echo '\${@: -1}' | cut -d' ' -f1-)': ~~~> ./a.sh $(echo "${@: -1}" | cut -d' ' -f1-):"
  ./a.sh $(echo "${@: -1}" | cut -d' ' -f1-)
  
  echo -e "\n'~~> ./a.sh \"\${@: -4}\"': ~~~> ./a.sh ${@: -4}:"
  ./a.sh "${@: -4}"
  
  echo -e "\n'~~> ./a.sh \$(echo '\${@: -\$(( \$#-1 ))}' | cut -d' ' -f1-)': ~~~> ./a.sh $(echo "${@: -$(( $#-1 ))}" | cut -d' ' -f1-)"
  ./a.sh $(echo "${@: -$(( $#-1 ))}" | cut -d' ' -f1-)

• a.sh

  echo """
  a.sh:
    \$1: "$1"
    \$#: "$#"
    \$@: "$@"
    \${@: -$(( $#-2 ))}: ${@: -$(( $#-2 ))}
  """

• result

  $ ./b.sh 1 2 3 4 5
  
  b.sh:
    $1                 : 1
    $#                 : 5
    $@                 : 1 2 3 4 5
    ${@: -1}           : 5
    ${@: -2}           : 4 5
    ${@: -3}           : 4 5
    ${@: -$(( $#-1 ))} : 2 3 4 5
    $(echo '${@: -$(( $#-1 ))}' | cut -d' ' -f1-) : 2 3 4 5
  
  '~~> ./a.sh "${@: -1}"': ~~~> ./a.sh e:
  a.sh:
    $1: 5
    $#: 1
    $@: 5
    ${@: --1}: 5
  
  '~~> ./a.sh $(echo '${@: -1}' | cut -d' ' -f1-)': ~~~> ./a.sh 5:
  a.sh:
    $1: 5
    $#: 1
    $@: 5
    ${@: --1}: 5
  
  '~~> ./a.sh "${@: -4}"': ~~~> ./a.sh 2 3 4 5:
  a.sh:
    $1: b
    $#: 4
    $@: 2 3 4 5
    ${@: -2}: 4 5
  
  '~~> ./a.sh $(echo '${@: -$(( $#-1 ))}' | cut -d' ' -f1-)': ~~~> ./a.sh 2 3 4 5
  a.sh:
    $1: 2
    $#: 4
    $@: 2 3 4 5
    ${@: -2}: 4 5

Manual Case-Loop Parser

[!NOTE]

• ✅ Pros: Simple, portable

• ❌ Cons: No built-in validation or help

#!/usr/bin/env bash
# shellcheck disable=SC1079,SC1078

usage="""USAGE
\t$0\t[-h|--help] [-c|--clean] [-t|--tag <tag>] [-i|--image <image>]
\t\t\t[-v|--ver <new-version>] [-n|--name <name>]
\t\t\t[-p|--prop <key=value>]
"""

while test -n "$1"; do
  case "$1" in
    -c | --clean    ) clean=true        ; shift   ;;
    -t | --tag      ) tag=$2            ; shift 2 ;;
    -i | --image    ) image=$2          ; shift 2 ;;
    -v | --ver      ) ver=$2            ; shift 2 ;;
    -n | --name     ) name=$2           ; shift 2 ;;
    -p | --prop     ) prop=$2           ; shift 2 ;;
    -h | --help | * ) echo -e "${usage}"; exit 0  ;;
  esac
done

echo """
  clean : ${clean}
    tag : ${tag}
  image : ${image}
    ver : ${ver}
   name : ${name}
   prop : ${prop}
"""

• result

  $ ./longopts.sh -h
  USAGE
    ./longopts.sh [-h|--help] [-c|--clean] [-t|--tag <tag>] [-i|--image <image>]
                  [-v|--ver <new-version>] [-n|--name <name>]
                  [-p|--prop <key=value>]
  
  $ ./longopts.sh -c
    clean : true
      tag :
    image :
      ver :
     name :
     prop :
  
  $ ./longopts.sh -c -t 'ttt' -i 'iii' --ver '1.1.1' --name 'name'
    clean : true
      tag : ttt
    image : iii
      ver : 1.1.1
     name : name
     prop :

until [ -z "$1" ]; do # Until all parameters used up
  echo "\$@  : $@ "; shift ;
done

# result
$ ./shift.sh 1 2 3 4 5
$@  : 1 2 3 4 5
$@  : 2 3 4 5
$@  : 3 4 5
$@  : 4 5
$@  : 5

Bash Equals-Separated

for i in "$@"; do
  case $i in
    -e=* | --extension=*  ) EXTENSION="${i#*=}"  ;  shift    ;;
    -s=* | --searchpath=* ) SEARCHPATH="${i#*=}" ;  shift    ;;
    --default             ) DEFAULT=YES          ;  shift    ;;
    -* | --*              ) echo "Unknown option $i"; exit 1 ;;
    *                     )                                  ;;
  esac
done

echo "FILE EXTENSION  = ${EXTENSION}"
echo "SEARCH PATH     = ${SEARCHPATH}"
echo "DEFAULT         = ${DEFAULT}"
echo "Number files in SEARCH PATH with EXTENSION:" $(ls -1 "${SEARCHPATH}"/*."${EXTENSION}" | wc -l)

with one or more values

[!TIP]

• positional_args+=("$1") to add the arguments to an array one by one

var1=""
flag_verbose=false

# POSIX format using `while [ $# -gt 0 ]`
while [[ $# -gt 0 ]]; do
  case "$1" in
    -v|--verbose ) flag_verbose=true             ;  shift   ;;
    -f|--file    ) var1="$2"                     ;  shift 2 ;;
    --dry-run    ) dryrun=true                   ;  shift   ;;
    -*           ) echo "Unknown option: $1" >&2 ;  exit 1  ;;
    *            ) positional_args+=("$1")       ;  shift   ;;
  esac
done

additional params on --

#!/usr/bin/env bash
# shellcheck disable=SC2051,SC2086

VERBOSE=false
DEBUG=false
MEMORY=
AOPT=
while true; do
  case "$1" in
    -v | --verbose ) VERBOSE=true ; shift   ;;
    -d | --debug   ) DEBUG=true   ; shift   ;;
    -m | --memory  ) MEMORY="$2"  ; shift 2 ;;
    --             ) shift        ; AOPT=$@  ;  break ;;
    *              ) break                  ;;
  esac
done

echo """
  VERBOSE       : ${VERBOSE}
  DEBUG         : ${DEBUG}
  MEMORY        : ${MEMORY}
  AOPT          : ${AOPT}
"""

# example
$ ./param.sh -v -m '256Gi' -- --author 'marslo'
  VERBOSE       : true
  DEBUG         : false
  MEMORY        : 256Gi
  AOPT          : --author marslo

$ ./param.sh -v -- -m '256Gi' --author 'marslo'
  VERBOSE       : true
  DEBUG         : false
  MEMORY        :
  AOPT          : -m 256Gi --author marslo

shift with uncertain params

echo '---------------- before shift -------------------'
echo ".. \$# : $#"
echo ".. \$@ : $@"
echo ".. \$* : $*"

echo '---------------- after shift -------------------'
opt=''

while [[ $# -gt 0 ]]; do
  case "$1" in
    -*) opt+="$1 "; shift;;
     *) break            ;;
  esac
done

echo ".. \$#   : $#"
echo ".. \$@   : $@"
echo ".. \$*   : $*"
echo ".. \$opt : $opt"

if [[ 0 = "$#" ]]; then
  echo -e "\033[0;33mERROR: must provide at least one non-opt param\033[0m"
  exit 2
elif [[ 1 = "$#" ]]; then
  path=''
  params="$1"
else
  path=${*: -1}
  params=${*: 1:$#-1}
fi

echo '---------------- result -------------------'
echo ">> opt    : ${opt}"
echo ">> params : ${params}"
echo ">> path   : ${path}"

POSIX getopts Parser

[!NOTE]

• ✅ Pros: POSIX, built-in

• ❌ Cons: No long options, no multi-word values

while getopts "f:vd" opt; do
  case $opt in
    f  ) FILE="$OPTARG" ;;
    v  ) VERBOSE=true   ;;
    d  ) DRYRUN=true    ;;
    \? ) echo "Invalid option: -$OPTARG"; exit 1 ;;
  esac
done
shift $((OPTIND -1))

# Reset in case getopts has been used previously in the shell.
OPTIND=1
output_file=''
verbose=0

while getopts "h?vf:" opt; do
  case "$opt" in
    h|\? ) show_help; exit 0   ;;
    v    ) verbose=1           ;;
    f    ) output_file=$OPTARG ;;
  esac
done

shift $((OPTIND-1))
[ "${1:-}" = "--" ] && shift

echo "verbose=$verbose, output_file='$output_file', Leftovers: $@"

GNU getopt Parser

[!NOTE]

• MacOS: brew install gnu-getopt

• ✅ Pros: Short + long, nice user UX

• ❌ Cons: Not portable across BSD/macOS by default (GNU-only)

#!/usr/bin/env bash

ARGS=$(getopt -o f:vd -l file:,verbose,dry-run -- "$@")
eval set -- "$ARGS"

while true; do
  case "$1" in
    -f|--file    ) FILE="$2"    ;  shift 2 ;;
    -v|--verbose ) VERBOSE=true ;  shift   ;;
    --dry-run    ) DRYRUN=true  ;  shift   ;;
    --           ) shift        ;  break   ;;
    *            ) break                   ;;
  esac
done

# option --output/-o requires 1 argument
LONGOPTS=debug,force,output:,verbose
OPTIONS=dfo:v

! PARSED=$(getopt --options=$OPTIONS --longoptions=$LONGOPTS --name "$0" -- "$@")
if [[ ${PIPESTATUS[0]} -ne 0 ]]; then
  # e.g. return value is 1
  #  then getopt has complained about wrong arguments to stdout
  exit 2
fi
# read getopt’s output this way to handle the quoting right:
eval set -- "$PARSED"

d=n f=n v=n outFile=-
# now enjoy the options in order and nicely split until we see --
while true; do
  case "$1" in
    -d|--debug   ) d=y          ;  shift            ;;
    -f|--force   ) f=y          ;  shift            ;;
    -v|--verbose ) v=y          ;  shift            ;;
    -o|--output  ) outFile="$2" ;  shift 2          ;;
    --           ) shift        ;  break            ;;
    *            ) echo "Programming error"; exit 3 ;;
  esac
done

# handle non-option arguments
if [[ $# -ne 1 ]]; then
    echo "$0: A single input file is required."
    exit 4
fi

echo "verbose: $v, force: $f, debug: $d, in: $1, out: $outFile"

bash-argparse Library

[!NOTE]

• Anvil/bash-argsparse
• ✅ Pros: Clean, descriptive, built-in help

• ❌ Cons: Bash-only, external lib needed

# requires sourcing the library
source argparse.sh

argparse "$@" <<EOF
--file -f [arg]    Path to the file
--verbose -v       Enable verbose output
--dry-run          Enable dry-run mode
EOF

docopts

[!NOTE]

• docopt/docopt
• ✅ Pros: Elegant, self-documenting

• ❌ Cons: Requires Python + docopts installed

# usage section (docopts parses this!)
read -r -d '' usage <<EOF
Usage:
  script.sh [-v|--verbose] [--dry-run] -f <file>
Options:
  -f --file=<file>     File to process
  -v --verbose         Verbose output
  --dry-run            Simulate actions
EOF

eval "$(docopts -A args -h "$usage" : "$@")"

# access like $args_file, $args_verbose, $args_dry_run

argbash Code Generator

[!NOTE]

• argbash.dev | matejak/argbash
• ✅ Pros: Auto-generates robust scripts

• ❌ Cons: Requires preprocessing step

# ARG_POSITIONAL_SINGLE([file], [File to process])
# ARG_OPTIONAL_BOOLEAN([verbose], [v], [Enable verbose])
# ARG_OPTIONAL_BOOLEAN([dry-run], [], [Dry run mode])
# ARG_HELP([Script to demonstrate argbash])
# ARGBASH_GO()

# The above is preprocessed by `argbash` into full Bash script

shflags (Google-style shell option lib)

[!NOTE]

• shflags | lib/shflags/shflags | kward/shflags
• ✅ Pros: Easy-to-read, Google-style

• ❌ Cons: Needs external lib and sourcing

. ./shflags

DEFINE_string 'file' '' 'file to use' 'f'
DEFINE_boolean 'verbose' false 'verbose mode' 'v'
DEFINE_boolean 'dry-run' false 'simulate mode' ''

FLAGS "$@" || exit 1
eval set -- "${FLAGS_ARGV}"

echo "File: ${FLAGS_file}"

references

• 如何在 Bash 中解析命令行参数？