How to create list in shell using for loop

Question

I am trying to create a new array using for loop

Images="alpine ubuntu centos"


Image_tags="$(for i in $Images; do
r_madoori1/$i
done)"


echo $Image_tags

I am expecting

Image_tags="r_madoori1/alpine r_madoori1/ubuntu r_madoori1/centos"

instead i am getting below error

./shell.sh: line 7: r_madoori1/alpine: No such file or directory
./shell.sh: line 7: r_madoori1/ubuntu: No such file or directory
./shell.sh: line 7: r_madoori1/centos: No such file or directory

Arrays are a ksh/bash/zsh/etc feature not available in sh. But string="item1 item2 item3" isn't an array at all (that would be array=( item1 item2 item3 )), so it's not clear what you're asking for. — Charles Duffy
– Charles Duffy, Commented Jul 21, 2021 at 16:56
@Rajeshwerwer : From the error message, it seems to me that your script is not run by bash. Please output echo $BASH_VERSION to check this. Also, you don't have any array in your code, and in the title of your question speaks of a list, not an array. Please be clear in what you want to achieve. — user1934428
– user1934428, Commented Jul 22, 2021 at 9:06
@Rajeshwerwer : Thags bash and sh contradict each other. Please remove one of them, and make up your mind, which shell you want to use. — user1934428
– user1934428, Commented Jul 22, 2021 at 9:08
You just forgot to add a printf '%s ' in front of r_madoori1/$i. — Socowi
– Socowi, Commented Jul 22, 2021 at 15:09

anubhava · Accepted Answer · 2021-07-21 17:50:54Z

2

Without using any loop you can do this in bash:

Images="alpine ubuntu centos"

Image_tags="r_madoori1/${Images// / r_madoori1\/}"

echo "$Image_tags"

Output:

r_madoori1/alpine r_madoori1/ubuntu r_madoori1/centos

edited Jul 21, 2021 at 17:50

answered Jul 21, 2021 at 16:54

anubhava

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2 Comments

Charles Duffy Over a year ago

This is bash-only, correct? Might want to make that explicit since this is also tagged sh.

anubhava Over a year ago

Thanks, I have added it now. Didn't notice sh tag earlier.

chepner · Accepted Answer · 2021-07-21 21:41:17Z

2

The for loop repeats commands; it's doesn't build a list of values. You could write something like

# OK
Image_tags="$(for i in $Images; do
 echo -n "r_madoori1/$i "
done)"

but it would be simpler to perform multiple assignments from the, rather than embed a loop in a single assignment.

# Better
for i in $Images; do
  Image_tags="$Image_tags r_madoori1/$i"
done

If you are using bash, though, you should use real arrays, not space-separated strings.

# Best
Images=(alpine ubuntu centos)
for i in "${Images[@]}"; do
  Image_tags+=( "r_maddori1/$i" )
done

or more concisely

Images=(alpine ubuntu centos)
Image_tags=("${Images[@]/#/r_madoori1/}")

edited Jul 21, 2021 at 21:41

answered Jul 21, 2021 at 16:53

chepner

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7 Comments

Yagami Over a year ago

But it is only printing 1st element in array r_maddori1/alpine r_maddori1/alpine r_maddori1/alpine i am expecting r_maddori1/alpine r_maddori1/ubuntu r_maddori1/centos

chepner Over a year ago

Did you mistype something? I can't reproduce that.

Yagami Over a year ago

Images=(alpine ubuntu centos) for i in $Images; do Image_tags="$Image_tags r_madoori1/$i" echo $Image_tags done I tried this

chepner Over a year ago

Images=(...) and Images="..." are two different values. You aren't using the real array properly. Please look at the third example carefully.

Philippe Over a year ago

@CharlesDuffy Indeed, this should be fine : Image_tags=("${Images[@]/#/r_madoori1/}")

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