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Bash Script Linter

Paste a shell script and find the bugs that only show up on the server — unquoted variables, #!/bin/sh scripts using bash-only syntax, rm -rf $VAR, unclosed fi. Every warning is explained in plain English, with the exact line and column.

Input

Your script

Nothing is uploaded — the check runs in this tab. Paste the whole file, shebang included, so the dialect check works.

1 line(s) checked.

Result

Summary

Pattern-based checker for the common, high-impact bash mistakes — it is not a full ShellCheck implementation and will not catch everything. Run it through ShellCheck for full analysis
Shebang
No shebang detected
Errors
0
Warnings
1
Notes
0

Paste a script above, or load the sample, to check it.

Applied 1 fix(es): 1 × shebang added

Findings

What will break, and why

Correctness bugs only — no style or portability preferences.

SeverityLine:ColRuleMessageFix
warning1:1WX100

No shebang line

Without a #! line, what runs the script depends entirely on how it is invoked. "./script.sh" hands it to whatever the kernel falls back to, cron runs it under /bin/sh, and your interactive test under bash works fine — so it passes locally and fails as a cron job.

Add as the very first line: #!/usr/bin/env bash

Reference

Common mistakes cheat sheet

The bugs this linter looks for, and the shape of the fix. These are the ones that survive local testing and fail in production.

Always quote expansions

✗cp $src $dst
✓cp "$src" "$dst"

Unquoted, the value is split on whitespace and then glob-expanded. One path with a space becomes two arguments.

"$@", never $@

✗mycmd $@
✓mycmd "$@"

"$@" is the only form that passes every argument through exactly as received, including empty ones.

[[ ]] is bash, [ ] is POSIX

✗#!/bin/sh … [[ -f $f ]]
✓#!/bin/sh … [ -f "$f" ]

On Debian and Ubuntu /bin/sh is dash. [[ does not exist there — "[[: not found" and the test is false.

Strings with =, numbers with -eq

✗[ "$n" = 10 ]
✓[ "$n" -eq 10 ]

= compares text, so "010" ≠ "10". -eq compares integers and errors loudly on non-numeric input.

cd can fail

✗cd /srv/app rm -rf ./cache
✓cd /srv/app || exit 1 rm -rf ./cache

If cd fails the script continues in the previous directory — and the next relative command hits the wrong tree.

Guard rm against an empty variable

✗rm -rf $DIR/
✓rm -rf "${DIR:?DIR is not set}"/

An unset $DIR makes this "rm -rf /". ${VAR:?msg} aborts instead of expanding to nothing.

Never read and write one file

✗sort f.txt > f.txt
✓sort f.txt > f.tmp && mv f.tmp f.txt

The redirect truncates the file before sort opens it, so you are left with an empty file.

Assignments take no spaces

✗NAME = value
✓NAME=value

With spaces the shell runs NAME as a command. The variable is never set and every later $NAME is empty.

Glob the directory, do not parse ls

✗for f in $(ls *.log)
✓for f in *.log

ls output is one string that gets split on whitespace, so filenames with spaces split into pieces.

read needs -r

✗while read line
✓while IFS= read -r line

Without -r, backslashes are eaten. Without IFS=, leading and trailing whitespace is stripped.

$? is only the last command

✗mycmd echo done [ $? -ne 0 ]
✓if ! mycmd; then …

The echo resets $?. Test the command directly rather than inspecting the status later.

Fail fast, fail loudly

✗#!/bin/bash
✓#!/bin/bash set -euo pipefail

-e stops on the first failure, -u catches typoed variable names, pipefail makes a broken pipeline fail.

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