ShellCheck

Name: shellcheck
Rating: 92
Author: mhalder

Lint shell scripts and fix common issues using ShellCheck.

Instructions

•Run ShellCheck on the script
•Analyze findings by severity
•Explain each issue clearly
•Provide fixes for each issue

Run ShellCheck

bash

# Basic check
shellcheck script.sh

# With severity filter
shellcheck --severity=warning script.sh

# Specific shell dialect
shellcheck --shell=bash script.sh

# Output formats
shellcheck --format=json script.sh
shellcheck --format=gcc script.sh

# Check multiple files
shellcheck *.sh

Common issues and fixes

SC2086: Double quote to prevent globbing

bash

# Bad
rm $file
echo $var

# Good
rm "$file"
echo "$var"

SC2046: Quote command substitution

bash

# Bad
rm $(find . -name "*.tmp")

# Good
rm "$(find . -name "*.tmp")"
# Or for multiple results:
find . -name "*.tmp" -delete

SC2006: Use $() instead of backticks

bash

# Bad
date=`date`

# Good
date=$(date)

SC2164: Use cd ... || exit

bash

# Bad
cd /some/dir
do_something

# Good
cd /some/dir || exit 1
do_something

SC2155: Declare and assign separately

bash

# Bad
local var=$(command)

# Good
local var
var=$(command)

SC2162: Read without -r mangles backslashes

bash

# Bad
read line

# Good
read -r line

SC2034: Variable appears unused

bash

# Check if it's exported or used in eval/source
# Or prefix with _ to indicate intentionally unused
_unused_var="value"

Disable warnings

bash

# Disable for next line
# shellcheck disable=SC2086
echo $unquoted_var

# Disable for entire file (at top)
# shellcheck disable=SC2034,SC2086

# Disable for block
# shellcheck disable=SC2086
{
    echo $var1
    echo $var2
}

Output format

code

## Issues Found

### Errors (must fix)
- Line 10, SC2086: Double quote to prevent globbing and word splitting

### Warnings (should fix)
- Line 15, SC2155: Declare and assign separately to avoid masking return values

### Suggestions
- Line 20, SC2034: UNUSED_VAR appears unused (verify or prefix with _)

## Fixed Code
[Show corrected version]

Rules

•MUST run shellcheck before reviewing manually
•MUST explain why each issue matters
•MUST provide specific fix for each issue
•Never ignore errors (SC level error)
•Always explain when disabling is appropriate
•Offer to auto-fix simple issues with Edit tool