How to split a environment variable based on delimiter in Docker

December 17, 2021

I am trying to split the following string into array on delimiter

str="We;Welcome;You;On;Javatpoint"

I manage to find a solution in bash that is

#!/bin/bash  
#Example for bash split string by another string  
  
str="We;Welcome;You;On;Javatpoint"  
delimiter=";"  
s=$str$delimiter  
array=();  
while [[ $s ]];  
do  
array+=( "${s%%"$delimiter"*}" );  
s=${s#*"$delimiter"};  
done;  
declare -p array

Results in

array=([0]="We" [1]="Welcome" [2]="You" [3]="On" [4]="Javatpoint")

I need to split the string into an array inside Dockerfile.

DOCKERFILE:

> FROM python:3.7-slim
> 
> ENV IN="We;Welcome;You;On;Javatpoint"

>Solution :

Just let bash do the splitting.

IFS=';' read -r -a array <<<"str"

or similar with readarray for multiline variables.

inside Dockerfile

If you want to use bash features make sure first that you are runnig Bash. RUN commands in dockerfile by default sexecute /bin/sh (see dockerfile reference documentation) which may not be Bash and may not support Bash arrays.

In this specific case, to be /bin/sh compatible, replace ; for a newline (tr) and read it as a newline separated stream or use word-splitting if there are no other whitespaces. See https://mywiki.wooledge.org/BashFAQ/001