Looping over comma-separated values in Bash#

Given a file (or a process) that produces comma separated values, here’s how to split those into separate variables and use them in a bash script.

The trick is to set the Bash IFS to a delimiter, then use my_array=($my_string) to split on that delimiter.

Create a text file called data.txt containing this:

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first,1
2
second,2

You can create that by doing:

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echo 'first,1
2
second,2' > /tmp/data.txt

To loop over that file and print each line:

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for line in $(cat /tmp/data.txt);
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do
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  echo $line
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done

To split each line into two separate variables in the loop, do this:

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for line in $(cat /tmp/data.txt);
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do
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  IFS=$','; split=($line); unset IFS;
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  # $split is now a bash array
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  echo "Column 1: ${split[0]}"
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  echo "Column 2: ${split[1]}"
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done

Outputs:

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Column 1: first
2
Column 2: 1
3
Column 1: second
4
Column 2: 2

Here’s a script I wrote using this technique for the TIL Use labels on Cloud Run services for a billing breakdown:

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#!/bin/bash
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for line in $(
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  gcloud run services list --platform=managed \
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    --format="csv(SERVICE,REGION)" \
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    --filter "NOT metadata.labels.service:*" \
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  | tail -n +2)
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do
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  IFS=$','; service_and_region=($line); unset IFS;
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  service=${service_and_region[0]}
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  region=${service_and_region[1]}
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  echo "service: $service    region: $region"
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  gcloud run services update $service \
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    --region=$region --platform=managed \
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    --update-labels service=$service
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  echo
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done