184

Is there any easy way to pass (receive) named parameters to a shell script?

For example,

my_script -p_out '/some/path' -arg_1 '5'

And inside my_script.sh receive them as:

# I believe this notation does not work, but is there anything close to it?
p_out=$ARGUMENTS['p_out']
arg1=$ARGUMENTS['arg_1']

printf "The Argument p_out is %s" "$p_out"
printf "The Argument arg_1 is %s" "$arg1"

Is this possible in Bash or Zsh?

2

12 Answers 12

218

If you don't mind being limited to single-letter argument names i.e. my_script -p '/some/path' -a5, then in bash you could use the built-in getopts, e.g.

#!/bin/bash

while getopts ":a:p:" opt; do
  case $opt in
    a) arg_1="$OPTARG"
    ;;
    p) p_out="$OPTARG"
    ;;
    \?) echo "Invalid option -$OPTARG" >&2
    ;;
  esac
done

printf "Argument p_out is %s\n" "$p_out"
printf "Argument arg_1 is %s\n" "$arg_1"

Then you can do

$ ./my_script -p '/some/path' -a5
Argument p_out is /some/path
Argument arg_1 is 5

There is a helpful Small getopts tutorial or you can type help getopts at the shell prompt.

5
  • 28
    This should be the accepted answer – Kaushik Ghose May 21 '15 at 13:38
  • 7
    I know this is a bit old, but why only 1 letter for the arguments? – Kevin Apr 28 '17 at 15:54
  • 2
    I implemented this (but with i and d). When I run it with my_script -i asd -d asd I get an empty string for the d argument. When I run it my_script -d asd -i asd I get empty string for both arguments. – Milkncookiez Feb 14 '18 at 22:48
  • 4
    @Milkncookiez -- I had a similar problem -- I didn't include a ':' after the last argument (a 'w' in my case). Once I added the ':' it started working as expected – Derek May 24 '18 at 15:30
  • 2
    @KaushikGhose Just fixed it. I guess better late than never. I wish SO notified you when an answer other than the one you accepted got more accepted votes. – Amelio Vazquez-Reina Jan 9 '20 at 12:47
56

I stole this from drupal.org, but you could do something like this:

while [ $# -gt 0 ]; do
  case "$1" in
    --p_out=*)
      p_out="${1#*=}"
      ;;
    --arg_1=*)
      arg_1="${1#*=}"
      ;;
    *)
      printf "***************************\n"
      printf "* Error: Invalid argument.*\n"
      printf "***************************\n"
      exit 1
  esac
  shift
done

The only caveat is that you have to use the syntax my_script --p_out=/some/path --arg_1=5.

2
  • 13
    The caveat is not necessary. :) You can have the conditions as follows: -c|--condition) – Milkncookiez May 30 '17 at 14:27
  • Docs to truncate string in variable (and to continue the trend in this thread, this should be the accepted answer). – toraritte Aug 8 '20 at 16:31
54

I use this script and works like a charm:

for ARGUMENT in "$@"
do

    KEY=$(echo $ARGUMENT | cut -f1 -d=)
    VALUE=$(echo $ARGUMENT | cut -f2 -d=)   

    case "$KEY" in
            STEPS)              STEPS=${VALUE} ;;
            REPOSITORY_NAME)    REPOSITORY_NAME=${VALUE} ;;     
            *)   
    esac    


done

echo "STEPS = $STEPS"
echo "REPOSITORY_NAME = $REPOSITORY_NAME"

Usage

bash my_scripts.sh  STEPS="ABC" REPOSITORY_NAME="stackexchange"

Console result :

STEPS = ABC
REPOSITORY_NAME = stackexchange

STEPS and REPOSITORY_NAME are ready to use in the script.

It does not matter what order the arguments are in.

6
  • 4
    This is neat and should be the accepted answer. – miguelmorin Feb 1 '19 at 17:07
  • This is a neat solution, but it seems to take a long time to parse, like 5 to 10 seconds on my PC, is this normal behavior? – Astronaut Dec 13 '19 at 14:01
  • mmm in my case it is instantaneous. – JRichardsz Dec 13 '19 at 17:22
  • This is neat but assumes you have = delimiter between the key and the value. I.e. you can't pass a value with a space like so: -p 3000 or --port 3000 – Jerry Green Nov 4 '20 at 10:32
  • Unfortunately this breaks if the value has an equals in it like this MYVAR="PROPERTIES_LIST":"\"apim=true&whichvalue=345\"" – PaulNUK Apr 12 at 13:43
39

The probably closest syntax to that is:

p_out='/some/path' arg_1='5' my_script
7
  • 8
    Related to this, if the -k option is set in the calling shell, then my_script p_out='/some/path' arg_1='5' has the same effect. (All arguments in the form of an assignment are added to the environment, not just those assignments preceding the command.) – chepner May 14 '14 at 22:55
  • 14
    I used to love this syntax, but it has a BIG caveat: after the command/function execution, those variables will still be defined in the current scope ! E.g.: x=42 echo $x; echo $x Which means in the next execution of my_script, if p_out is omitted, it will stick to the value passed the last time !! ('/some/path') – Lucas Cimon Sep 1 '15 at 9:13
  • @LucasCimon Can you not unset them after the first execution, reset them before the next execution? – Nikos Alexandris Dec 18 '17 at 15:46
  • 2
    @LucasCimon That is not correct. x=42 echo $x does not even output anything if $x was not defined before. – Hauke Laging Mar 22 '18 at 11:02
  • You're right @HaukeLaging, thanks for correcting that – Lucas Cimon Apr 19 '18 at 9:01
18

With zsh, you'd use zparseopts:

#! /bin/zsh -
zmodload zsh/zutil
zparseopts -A ARGUMENTS -p_out: -arg_1:

p_out=$ARGUMENTS[--p_out]
arg1=$ARGUMENTS[--arg_1]

printf 'Argument p_out is "%s"\n' "$p_out"
printf 'Argument arg_1 is "%s"\n' "$arg_1"

But you'd call the script with myscript --p_out foo.

Note that zparseopts doesn't support abbreviating long options or the --p_out=foo syntax like GNU getopt(3) does.

2
  • Do you know why the zparseopts uses just one dash for the arguments whereas in the [] it is 2 dashes? Does not make sense! – Timo Nov 7 '17 at 14:59
  • @Timo, see info zsh zparseopts for details – Stéphane Chazelas Nov 7 '17 at 16:20
15

I just came up with this script

while [ $# -gt 0 ]; do

   if [[ $1 == *"--"* ]]; then
        v="${1/--/}"
        declare $v="$2"
   fi

  shift
done

pass it like my_script --p_out /some/path --arg_1 5 and then in the script you can use $arg_1 and $p_out.

1
  • I like this solution in KSH88 I had to v=``echo ${1} | awk '{print substr($1,3)}'`` typeset $v="$2" (Remove one backtick each side) – hol Sep 24 '18 at 9:45
9

I found the solution from cdmo the best, because it is not only limited to a single letter. With a slight adjustment it will consume either whitespace separated arguments like --url www.example.com and those with an assignment like, for example the synonym parameter -u=www.example.com. Even flag arguments can be parsed:

while [ $# -gt 0 ]; do
  case "$1" in
    --url*|-u*)
      if [[ "$1" != *=* ]]; then shift; fi # Value is next arg if no `=`
      URL="${1#*=}"
      ;;
    --file*|-f*)
      if [[ "$1" != *=* ]]; then shift; fi
      FILE="${1#*=}"
      ;;
    --help|-h)
      printf "Meaningful help message" # Flag argument
      exit 0
      ;;
    *)
      >&2 printf "Error: Invalid argument\n"
      exit 1
      ;;
  esac
  shift
done
1
  • syntax error near unexpected token `)' *) Worked when I added ;; after exit 0 – tim May 5 '20 at 23:41
6

This answer was initially an edit of @cdmo's answer (thanks to @Milkncookiez's comment also!), that got rejected as expected, so here it goes:

#!/usr/bin/env bash

while [ $# -gt 0 ]; do
  case "$1" in
    -p|-p_out|--p_out)
      p_out="$2"
      ;;
    -a|-arg_1|--arg_1)
      arg_1="$2"
      ;;
    *)
      printf "***************************\n"
      printf "* Error: Invalid argument.*\n"
      printf "***************************\n"
      exit 1
  esac
  shift
  shift
done

The below invocations are all equivalent:

$ ./my-script.sh -a "lofa" -p "miez"
$ ./my-script.sh -arg_1 "lofa" --p_out "miez"
$ ./my-script.sh --arg_1 "lofa" -p "miez"

When using the variables, one can make sure that they have a default value set by using "${p_out:-"default value"}" for example.

1
1

I made a combination of some approaches recommended here. In my case, I need a script that could handle arguments in this format: --arg1=test So I used the following:

args=()

for argument in "$@"
do

    key=$(echo $argument | cut -f1 -d=)
    value=$(echo $argument | cut -f2 -d=)   

    if [[ $key == *"--"* ]]; then
        v="${key/--/}"
        declare $v="${value}" 
   fi
done

args+=( '--local_dir' ${local_dir})
args+=( '--format' ${format})

python3 ./test.py "${args[@]}"

You can see that I added the arguments together to call a python script with those arguments: test_script.sh --local_dir=test --format=other

Thanks to Shahzad Malik and JRichardsz, for the guide to join the two approaches.

0

I have just made this one. It doesn't require "=" and supports non-valued parameters. Mind the need of additional shift commands for valued parameters.

#!/bin/bash

if [ $# -eq 0 ]; then
    printf "Utilizacao:\n"
    printf "$0 [[--imagem_inicial|-i] <tag_inicial>] [[--imagem_final|-f] <tag_final>] [--verbose|-v]\n"
    exit 1
fi

while [ $# -gt 0 ]; do
  case "$1" in
    --imagem_inicial|-i)
      export tag_imagem_inicial="${2}"
      shift
      ;;
    --imagem_final|-f)
      export tag_imagem_final="${2}"
      shift
      ;;
    --verbose|-v)
      export verbose_option=1
      ;;
    *)
      printf "ERRO: Parametros invalidos\n"
      printf "Execute sem parametros para a sintaxe.\n"
      exit 1
  esac
  shift
done

echo tag_imagem_inicial=${tag_imagem_inicial}
echo tag_imagem_final=${tag_imagem_final}
-2

If a function or an application has more than zero arguments, it always has a last argument.

If you want to read option flag and value pairs, as in: $ ./t.sh -o output -i input -l last

And you want to accept a variable number of option/value pairs,

And do not want a huge "if .. then .. else .. fi" tree,

Then after checking for an argument count of non-zero and even,

Write a while loop with these four eval statements as the body, followed by a case statement using the two values determined in each pass through the loop.

The tricky part of the scripting is demonstrated here:

#!/bin/sh    

# For each pair - this chunk is hard coded for the last pair.
eval TMP="'$'$#"
eval "PICK=$TMP"
eval TMP="'$'$(($#-1))"
eval "OPT=$TMP"

# process as required - usually a case statement on $OPT
echo "$OPT \n $PICK"

# Then decrement the indices (as in third eval statement) 

:<< EoF_test
$ ./t.sh -o output -i input -l last
-l 
last
$ ./t.sh -o output -l last
-l 
last
$ ./t.sh  -l last
-l 
last
EoF_test
-3
mitsos@redhat24$ my_script "a=1;b=mitsos;c=karamitsos"
#!/bin/sh
eval "$1"

you've just injected command line parameters inside script scope !!

1
  • 3
    This doesn't work with the syntax the OP specified; they want -a 1 -b mitsos -c karamitsos – Michael Mrozek Feb 18 '15 at 14:48

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