For Loop variable in Bash Script [duplicate]

Question

I am trying to execute this script as bash test.sh

#!/bin/bash
for region in "aws ec2 describe-regions --output text | cut -f4";
  do 
     echo -e "\nListing Instances in region:'$region'...";
      aws ec2 describe-instances --region $region;
done

But the only output that I get for $region is the print of the command. so it says "Listing Instances aws ec2 describe-regions .. "

How can I fix this ?

See BashPitfalls #1 for a brief discussion of why for variable in $(anything) is a bad idea, and BashFAQ #1 for a discussion of how to correctly iterate over lines of input one at a time. — Charles Duffy
– Charles Duffy, Commented Feb 22, 2021 at 20:00
(Also, echo -e is itself better avoided, as it's wildly nonportable (not just between shells, but even between runtime configurations when your shell is known to be bash); see Why is printf better than echo? at Unix & Linux). — Charles Duffy
– Charles Duffy, Commented Feb 22, 2021 at 20:01
(also, using a .sh extension on a bash script is not great practice; it implies that it's a sh script, but bash and sh are two different languages; also, executable scripts are executables, and executables on UNIX typically don't have extensions at all -- you run ls, not ls.elf; similarly, one runs pip, not pip.py). — Charles Duffy
– Charles Duffy, Commented Feb 22, 2021 at 20:04

chepner · Accepted Answer · 2021-02-22 19:40:45Z

1

You aren't executing a command; you are iterating over a sequence containing exactly one element, the strings aws ec2 ...

You need a command substitution to actually execute the command:

for region in $(aws ec2 describe-regions --output text | cut -f4); do
    echo -e ...
    aws ec2 describe-instances --region "$region"
done

answered Feb 22, 2021 at 19:40

chepner

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1 Comment

Charles Duffy Over a year ago

....though that's not the best way to iterate over aws ec2's output, as discussed in Don't Read Lines With For.

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