How do I convert command-line arguments into a bash script array?
I want to take this:
./something.sh arg1 arg2 arg3and 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 [ "$#" -eq 0 ]; then myArray=( defaultarg1 defaultarg2 )
else myArray=( "$@" )
fi7 Answers
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 "$@"
apple banana kiwi fruitUnderstanding how to use the argument structure is particularly useful in POSIX sh, which has nothing else like an array.
7Maybe this can help:
myArray=("$@") also you can iterate over arguments by omitting 'in':
for arg; do echo "$arg"
donewill be equivalent
for arg in "${myArray[@]}"; do echo "$arg"
doneActually 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}"; done12 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 lllFor your specific case, this could be used (without the need for arrays), to set the list of arguments when none was given:
if [ "$#" -eq 0 ]; then set -- defaultarg1 defaultarg2
fiwhich translates to this even simpler expression:
[ "$#" == "0" ] && set -- defaultarg1 defaultarg2Here is another usage :
#!/bin/bash
array=( "$@" )
arraylength=${#array[@]}
for (( i=0; i<${arraylength}; i++ ));
do echo "${array[$i]}"
doneEasier 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 $stuff ; done ; } echoarg Hey Ho Lets Go Hey Ho Lets GoThe importance of the double quotes is worth emphasizing. Suppose an argument contains whitespace.
Code:
#!/bin/bash
printf 'arguments:%s\n' "$@"
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]}"
doneOutput:
> ./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.
> 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 4Output:
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
