set -e Will Kill Your Script For No Good Reason

set -e Will Kill Your Script For No Good Reason

You add set -e to your bash script because you want it to stop on errors. Reasonable expectation. What could go wrong?

Plenty.

The Problem

set -e makes your script exit immediately when any command returns non-zero. Sounds fine until you remember how many things legitimately return non-zero:

grep -q "pattern" file    # returns 1 when no match found
curl -s https://example.com  # returns non-zero on 4xx/5xx
(( counter > 5 ))          # returns 1 when false

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None of those are errors. But set -e doesn't care.

Real Example

#!/bin/bash
set -e

# This fails silently when the string isn't found
name=$(grep "^username=" /etc/app/config | cut -d= -f2)

# This fails when count is zero  
if (( count > 0 )); then
    process_items
fi

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The grep returns 1 when there's no match. set -e kills the script. Same with arithmetic that's false.

The Workarounds

Option 1: Disable locally

set -e
grep -q "pattern" file || true   # always succeeds

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Option 2: Toggle around suspect code

set +e
grep -q "pattern" file
result=$?
set -e

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Option 3: Check explicitly

if grep -q "pattern" file; then
    name=$(grep "^username=" /etc/app/config | cut -d= -f2)
fi

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The Smarter Default

Skip set -e entirely. Check your commands explicitly:

if ! grep -q "pattern" file; then
    echo "pattern not found" >&2
    exit 1
fi

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More verbose, but you control exactly what fails and why.

Why This Bites You At 3am

Because the script worked for months, then one day curl starts returning 404 for a URL that moved, and your whole deploy stops. The actual failure is trivial, but set -e treats it like the world ended.

It's not your logic that's broken. It's set -e being overprotective.

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This isn't a reason to never use set -e. Just don't use it without understanding what it actually checks. Most shell script bugs I debug come down to this flag surprising someone at the worst moment.