Adding a prefix to all array elements in Bash

Question

I am storing command line parameters in an array variable. (This is necessary for me). I wanted to prefix all the array values with a string passing through a variable.

PREFIX="rajiv"

services=$( echo $* | tr -d '/' )

echo  "${services[@]/#/$PREFIX-}"

I am getting this output.

> ./script.sh webserver wistudio
rajiv-webserver wistudio

But I am expecting this output.

rajiv-webserver rajiv-wistudio

codeforester · Accepted Answer · 2018-03-04 06:58:44Z

8

Your array initialization is wrong. Change it to this:

services=($(echo $* | tr -d '/'))

Without the outer (), services would become a string and the parameter expansion "${services[@]/#/$PREFIX-}" adds $PREFIX- to your string.

In situations like this, declare -p can be used to examine the contents of your variable. In this case, declare -p services should show you:

declare -a services=([0]="webserver" [1]="wistudio") # it is an array!

and not

declare -- services="webserver wistudio"             # it is a plain string

edited Mar 4, 2018 at 6:58

answered Mar 4, 2018 at 6:01

codeforester

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4 Comments

Rajiv Rai Over a year ago

Yes. It worked. can you please also tell me why it was wrong? because echo "$services[@]" would still give me the values correctly

Rajiv Rai Over a year ago

I would also like to know if consider it as a string then how would the solution work? in my another script i have to pass the appended value to a executable, Which accept only string.

codeforester Over a year ago

May be create another question with the details.

Gordon Davisson Over a year ago

echo $* still has many potential problems due to word splitting and wildcard expansion. I'd recommend using services=("${@//\//}") to create the array, since it'll work correctly with pretty much anything in the arguments.

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