Based on an associative array in a Bash script, I need to iterate over it to get the key and value.
#!/bin/bash
declare -A array
array[foo]=bar
array[bar]=foo
I actually don't understand how to get the key while using a for-in loop.
5 Answers
The keys are accessed using an exclamation point: ${!array[@]}, the values are accessed using ${array[@]}.
You can iterate over the key/value pairs like this:
for i in "${!array[@]}"
do
echo "key : $i"
echo "value: ${array[$i]}"
done
Note the use of quotes around the variable in the for statement (plus the use of @ instead of *). This is necessary in case any keys include spaces.
The confusion in the other answer comes from the fact that your question includes "foo" and "bar" for both the keys and the values.
answered Jun 24, 2010 at 19:31
Dennis Williamson
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7 Comments
Michael-O
This is now if assign all keys to an array:
array=(${!hash[@]})
Dennis Williamson
@Michael-O: You need to quote the parameter expansion to protect keys that may have whitespace:
array=("${!hash[@]}")Michael-O
@DennisWilliamson, thanks a lot. I didn't have this on my mind.
pkaramol
How can we use a function argument number instead of a variable? e.g.
for i in "${!$1[@]}" ?Dennis Williamson
@pkaramol: Starting in Bash 4.3 you can use namerefs. Example:
declare -A aa; aa['A']=a1; aa['B']=b2; aa['C']=c3; foo () { declare -n assoc=$1; for key in "${!assoc[@]}"; do echo "Key: $key; Value: ${assoc[$key]}"; done; }; foo aa. Please see BashFAQ/006 for some important information. |
You can access the keys with ${!array[@]}:
bash-4.0$ echo "${!array[@]}"
foo bar
Then, iterating over the key/value pairs is easy:
for i in "${!array[@]}"
do
echo "key :" $i
echo "value:" ${array[$i]}
done
3 Comments
MA1
echo "${!array[@]}" didn't work on my machine. I'm using mac.
plijnzaad
I noticed this too: it works on my Linux (which has bash version 4.4.20) but not on Mac (which has bash version 3.2.57) ...
piero B
This is not the only issue that default bash legacy version can cause on Macos... You need to begin your scripts with:
#!/usr/bin/env bash Then, if you have Xcode and command line tools up to date, your scripts will run with a more recent and comprehensive version of bash. As of today with Macos 26.1 I get bash 5.3.3 in my scripts instead of the 3.2.57 running bash --version in the TerminalUse this higher order function to prevent the pyramid of doom
foreach(){
arr="$(declare -p $1)" ; eval "declare -A f="${arr#*=};
for i in ${!f[@]}; do $2 "$i" "${f[$i]}"; done
}
example:
$ bar(){ echo "$1 -> $2"; }
$ declare -A foo["flap"]="three four" foo["flop"]="one two"
$ foreach foo bar
flap -> three four
flop -> one two
3 Comments
Alexej Magura
I'm not sure how this is applicable? Isn't pyramid of doom a purely aesthetic issue and really only applicable in object-oriented languages?
Bálint Szigeti
could you explain it? The foreach function is bit tricky. I don't get it.
Beni Cherniavsky-Paskin
declare/local arguments can be dynamic, can
local -A f="${arr#*=}" without risky eval.Welcome to input associative array 2.0!
clear
echo "Welcome to input associative array 2.0! (Spaces in keys and values now supported)"
unset array
declare -A array
read -p 'Enter number for array size: ' num
for (( i=0; i < num; i++ ))
do
echo -n "(pair $(( $i+1 )))"
read -p ' Enter key: ' k
read -p ' Enter value: ' v
echo " "
array[$k]=$v
done
echo " "
echo "The keys are: " ${!array[@]}
echo "The values are: " ${array[@]}
echo " "
echo "Key <-> Value"
echo "-------------"
for i in "${!array[@]}"; do echo $i "<->" ${array[$i]}; done
echo " "
echo "Thanks for using input associative array 2.0!"
Output:
Welcome to input associative array 2.0! (Spaces in keys and values now supported)
Enter number for array size: 4
(pair 1) Enter key: Key Number 1
Enter value: Value#1
(pair 2) Enter key: Key Two
Enter value: Value2
(pair 3) Enter key: Key3
Enter value: Val3
(pair 4) Enter key: Key4
Enter value: Value4
The keys are: Key4 Key3 Key Number 1 Key Two
The values are: Value4 Val3 Value#1 Value2
Key <-> Value
-------------
Key4 <-> Value4
Key3 <-> Val3
Key Number 1 <-> Value#1
Key Two <-> Value2
Thanks for using input associative array 2.0!
Input associative array 1.0
(keys and values that contain spaces are not supported)
clear
echo "Welcome to input associative array! (written by mO extraordinaire!)"
unset array
declare -A array
read -p 'Enter number for array size: ' num
for (( i=0; i < num; i++ ))
do
read -p 'Enter key and value separated by a space: ' k v
array[$k]=$v
done
echo " "
echo "The keys are: " ${!array[@]}
echo "The values are: " ${array[@]}
echo " "
echo "Key <-> Value"
echo "-------------"
for i in ${!array[@]}; do echo $i "<->" ${array[$i]}; done
echo " "
echo "Thanks for using input associative array!"
Output:
Welcome to input associative array! (written by mO extraordinaire!)
Enter number for array size: 10
Enter key and value separated by a space: a1 10
Enter key and value separated by a space: b2 20
Enter key and value separated by a space: c3 30
Enter key and value separated by a space: d4 40
Enter key and value separated by a space: e5 50
Enter key and value separated by a space: f6 60
Enter key and value separated by a space: g7 70
Enter key and value separated by a space: h8 80
Enter key and value separated by a space: i9 90
Enter key and value separated by a space: j10 100
The keys are: h8 a1 j10 g7 f6 e5 d4 c3 i9 b2
The values are: 80 10 100 70 60 50 40 30 90 20
Key <-> Value
-------------
h8 <-> 80
a1 <-> 10
j10 <-> 100
g7 <-> 70
f6 <-> 60
e5 <-> 50
d4 <-> 40
c3 <-> 30
i9 <-> 90
b2 <-> 20
Thanks for using input associative array!
1 Comment
EndlosSchleife
Downvoted because it's verbose and contains no new information.
declare -a arr
echo "-------------------------------------"
echo "Here another example with arr numeric"
echo "-------------------------------------"
arr=( 10 200 3000 40000 500000 60 700 8000 90000 100000 )
echo -e "\n Elements in arr are:\n ${arr[0]} \n ${arr[1]} \n ${arr[2]} \n ${arr[3]} \n ${arr[4]} \n ${arr[5]} \n ${arr[6]} \n ${arr[7]} \n ${arr[8]} \n ${arr[9]}"
echo -e " \n Total elements in arr are : ${arr[*]} \n"
echo -e " \n Total lenght of arr is : ${#arr[@]} \n"
for (( i=0; i<10; i++ ))
do echo "The value in position $i for arr is [ ${arr[i]} ]"
done
for (( j=0; j<10; j++ ))
do echo "The length in element $j is ${#arr[j]}"
done
for z in "${!arr[@]}"
do echo "The key ID is $z"
done
~
for i in a,b c_s,d ; do KEY=${i%,*}; VAL=${i#*,}; echo $KEY" XX "$VAL; done