CODEWITHSUNDEEP
arraysbashshell
Suman
Suman

Reputation: 9561

Convert command line arguments into an array in Bash

How do I convert command-line arguments into a bash script array?

I want to take this:

./something.sh arg1 arg2 arg3

and convert it to 

myArray=( arg1 arg2 arg3 )

so that I can use myArray for further use in the script.

This previous SO post comes close, but doesn't go into how to create an array: How do I parse command line arguments in Bash?

I need to convert the arguments into a regular bash script array; I realize I could use other languages (Python, for instance) but need to do this in bash. I guess I'm looking for an "append" function or something similar?

UPDATE: I also wanted to ask how to check for zero arguments and assign a default array value, and thanks to the answer below, was able to get this working:

if [ "$#" -eq 0 ]; then
  myArray=( defaultarg1 defaultarg2 )
else
  myArray=( "$@" )
fi

Upvotes: 246

Views: 249116

Answers (7)

kojiro
kojiro

Reputation: 77069

Actually your command line arguments are practically like an array already. At least, you can treat the $@ variable much like an array. That said, you can convert it into an actual array like this:

myArray=( "$@" )

If you just want to type some arguments and feed them into the $@ value, use set:

$ set -- apple banana 'kiwi fruit'
$ echo "$#"
3
$ echo "$@"
apple banana kiwi fruit
$ for arg in "${@}"; do echo -n ", $arg"; done
, apple, banana, kiwi fruit

Understanding how to use the argument structure is particularly useful in POSIX sh, which has nothing else like an array.

Upvotes: 296

Nahuel Fouilleul
Nahuel Fouilleul

Reputation: 19315

Maybe this can help:

myArray=("$@")

also you can iterate over arguments by omitting 'in':

for arg; do
   echo "$arg"
done

will be equivalent

for arg in "${@}"; do
   echo "$arg"
done

Upvotes: 87

tuğrul altun
tuğrul altun

Reputation: 161

Here is another usage :

#!/bin/bash
array=( "$@" )
arraylength=${#array[@]}
for (( i=0; i<${arraylength}; i++ ));
do
   echo "${array[$i]}"
done

Upvotes: 16

Jacob Wegelin
Jacob Wegelin

Reputation: 1306

The importance of the double quotes is worth emphasizing. Suppose an argument contains whitespace.

Code:

#!/bin/bash
printf 'arguments:%s\n' "$@"
declare -a arrayGOOD=( "$@" )
declare -a arrayBAAD=(  $@  )

printf '\n%s:\n' arrayGOOD
declare -p arrayGOOD
arrayGOODlength=${#arrayGOOD[@]}
for (( i=1; i<${arrayGOODlength}+1; i++ ));
do
   echo "${arrayGOOD[$i-1]}"
done

printf '\n%s:\n' arrayBAAD
declare -p arrayBAAD
arrayBAADlength=${#arrayBAAD[@]}
for (( i=1; i<${arrayBAADlength}+1; i++ ));
do
   echo "${arrayBAAD[$i-1]}"
done

Output:

> ./bash-array-practice.sh 'The dog ate the "flea" -- and ' the mouse.
arguments:The dog ate the "flea" -- and 
arguments:the
arguments:mouse.

arrayGOOD:
declare -a arrayGOOD='([0]="The dog ate the \"flea\" -- and " [1]="the" [2]="mouse.")'
The dog ate the "flea" -- and 
the
mouse.

arrayBAAD:
declare -a arrayBAAD='([0]="The" [1]="dog" [2]="ate" [3]="the" [4]="\"flea\"" [5]="--" [6]="and" [7]="the" [8]="mouse.")'
The
dog
ate
the
"flea"
--
and
the
mouse.
>

Upvotes: 4

Kirin
Kirin

Reputation: 29

Side-by-side view of how the array and $@ are practically the same.

Code:

#!/bin/bash

echo "Dollar-1 : $1"
echo "Dollar-2 : $2"
echo "Dollar-3 : $3"
echo "Dollar-AT: $@"
echo ""

myArray=( "$@" )

echo "A Val 0: ${myArray[0]}"
echo "A Val 1: ${myArray[1]}"
echo "A Val 2: ${myArray[2]}"
echo "A All Values: ${myArray[@]}"

Input: 

./bash-array-practice.sh 1 2 3 4

Output:

Dollar-1 : 1
Dollar-2 : 2
Dollar-3 : 3
Dollar-AT: 1 2 3 4

A Val 0: 1
A Val 1: 2
A Val 2: 3
A All Values: 1 2 3 4

Upvotes: 2

user2350426
user2350426

Reputation:

Actually the list of parameters could be accessed with $1 $2 ... etc.
Which is exactly equivalent to:

${!i}

So, the list of parameters could be changed with set,
and ${!i} is the correct way to access them: 

$ set -- aa bb cc dd 55 ff gg hh ii jjj kkk lll
$ for ((i=0;i<=$#;i++)); do echo "$#" "$i" "${!i}"; done

12 1 aa
12 2 bb
12 3 cc
12 4 dd
12 5 55
12 6 ff
12 7 gg
12 8 hh
12 9 ii
12 10 jjj
12 11 kkk
12 12 lll

For your specific case, this could be used (without the need for arrays), to set the list of arguments when none was given:

if [ "$#" -eq 0 ]; then
    set -- defaultarg1 defaultarg2
fi

which translates to this even simpler expression:

[ "$#" == "0" ] && set -- defaultarg1 defaultarg2

Upvotes: 24

runlevel0
runlevel0

Reputation: 2963

Easier Yet, you can operate directly on $@ ;)

Here is how to do pass a a list of args directly from the prompt: 

function echoarg { for stuff in "$@" ; do echo $stuff ; done ; } 

    echoarg Hey Ho Lets Go
    Hey
    Ho
    Lets
    Go

Upvotes: 5

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