Bash script eval with aws command producing "command not found"

Question

I have a short bash script to take in an int from a user to identify to select a certain eks cluster.

When I use eval $(aws eks --region us-east-1 update-kubeconfig --name eventplatform$input)

I get the error: Updated: command not found

This is resolved if I simply change the command to just aws eks --region us-east-1 update-kubeconfig --name eventplatform$input

Why is the eval command not working for this?

#!/usr/bin/env bash -e

read -p "Which cluster are you trying to access? (int >= 0): " input

while [[ -n ${input//[0-9]/} ]]
do
    read -p "Which cluster are you trying to access? (int >= 0): " input
done

eval $(aws eks --region us-east-1 update-kubeconfig --name eventplatform$input)

set -x is your friend to enable trace logging so you can see what's going on. That said, you almost certainly shouldn't be using eval here. What's the point of it? — Charles Duffy
– Charles Duffy, Commented Jul 19, 2022 at 19:20
(btw, set -e is generally a bad idea; it makes your script far harder for readers/reviewers to understand its behavior, not to mention authors. See the exercises section of BashFAQ #105) — Charles Duffy
– Charles Duffy, Commented Jul 19, 2022 at 19:21
The command you are using modifies your ~/.kube/config file. It does not output text that can be executed by a shell. — jordanm
– jordanm, Commented Jul 19, 2022 at 19:21
...also, if you are going to use eval, there is basically no circumstance where eval $(something) is more correct than eval "$(something)" -- the former breaks the output of something into words and expands each word as a glob expression before combining them back into a single string and trying to parse that string as code. But collect the xtrace log so we know what's happening during execution before trying to go down that road. — Charles Duffy
– Charles Duffy, Commented Jul 19, 2022 at 19:22
(also, it's arguably a bug that AWS is emitting their "Updated" message to stdout instead of stderr, which is where POSIX states that diagnostic data -- a category which includes status updates meant for human readers -- belongs). — Charles Duffy
– Charles Duffy, Commented Jul 19, 2022 at 19:25

Charles Duffy · Accepted Answer · 2022-07-19 19:26:06Z

2

The eval command isn't supposed to work for this (whatever you expect "work" to mean in this context).

eval runs data as code. Only programs that write well-formed shell commands or scripts to their stdout as data should have that data evaled.

answered Jul 19, 2022 at 19:26

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Charles Duffy

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1 Comment

xpusostomos Over a year ago

Yes. Eval is rarely useful. Eval is for advanced users, and most advanced users usually know better than to use it.

Shakiba Moshiri · Accepted Answer · 2022-07-20 08:36:23Z

1

Simple. eval argument should be a string or something that exists to run, not output of other comments

#!/bin/bash

eval "ls" # okay 
# file1.txt
# file2.txt

eval $(ls); # error
# bash: file1.txt: command not found

See help eval

eval: eval [arg ...] Execute arguments as a shell command.
Combine ARGs into a single string, use the result as input to the shell,
and execute the resulting commands.

edited Jul 20, 2022 at 8:36

answered Jul 20, 2022 at 8:29

Shakiba Moshiri

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