1# macOS with Homebrew
 2brew install shellcheck
 3
 4# Ubuntu/Debian
 5apt-get install shellcheck
 6
 7# From source
 8git clone https://github.com/koalaman/shellcheck.git
 9cd shellcheck
10make build
11make install
12
13# Verify installation
14shellcheck --version

1# Set default shell target
2export SHELLCHECK_SHELL=bash
3
4# Enable strict mode
5export SHELLCHECK_STRICT=true
6
7# Specify configuration file location
8export SHELLCHECK_CONFIG=~/.shellcheckrc

1# SC1004: Backslash continuation not followed by newline
2echo hello\
3world  # Error - needs line continuation
4
5# SC1008: Invalid data for operator `=='
6if [[ $var =  "value" ]]; then  # Space before ==
7    true
8fi

 1# SC2009: Consider using pgrep or pidof instead of grep|grep
 2ps aux | grep -v grep | grep myprocess  # Use pgrep instead
 3
 4# SC2012: Use `ls` only for viewing. Use `find` for reliable output
 5for file in $(ls -la)  # Better: use find or globbing
 6
 7# SC2015: Avoid using && and || instead of if-then-else
 8[[ -f "$file" ]] && echo "found" || echo "not found"  # Less clear
 9
10# SC2016: Expressions don't expand in single quotes
11echo '$VAR'  # Literal $VAR, not variable expansion
12
13# SC2026: This word is non-standard. Set POSIXLY_CORRECT
14# when using with scripts for other shells

 1# SC2086: Double quote to prevent globbing and word splitting
 2for i in $list; do  # Should be: for i in $list or for i in "$list"
 3    echo "$i"
 4done
 5
 6# SC2115: Literal tilde in path not expanded. Use $HOME instead
 7~/.bashrc  # In strings, use "$HOME/.bashrc"
 8
 9# SC2181: Check exit code directly with `if`, not indirectly in a list
10some_command
11if [ $? -eq 0 ]; then  # Better: if some_command; then
12
13# SC2206: Quote to prevent word splitting or set IFS
14array=( $items )  # Should use: array=( $items )

1# SC3010: In POSIX sh, use 'case' instead of 'cond && foo'
2[[ $var == "value" ]] && do_something  # Not POSIX
3
4# SC3043: In POSIX sh, use 'local' is undefined
5function my_func() {
6    local var=value  # Not POSIX in some shells
7}

1#!/bin/bash
2# Configure for maximum portability
3
4shellcheck \
5  --shell=sh \
6  --external-sources \
7  --check-sourced \
8  script.sh

1#!/bin/bash
2# Configure for Bash development
3
4shellcheck \
5  --shell=bash \
6  --exclude=SC1091,SC2119 \
7  --enable=all \
8  script.sh

 1#!/bin/bash
 2set -Eeuo pipefail
 3
 4# Analyze all shell scripts and fail on issues
 5find . -type f -name "*.sh" | while read -r script; do
 6    echo "Checking: $script"
 7    shellcheck \
 8        --shell=bash \
 9        --format=gcc \
10        --exclude=SC1091 \
11        "$script" || exit 1
12done

 1#!/bin/bash
 2# .git/hooks/pre-commit
 3
 4#!/bin/bash
 5set -e
 6
 7# Find all shell scripts changed in this commit
 8git diff --cached --name-only | grep '\.sh$' | while read -r script; do
 9    echo "Linting: $script"
10
11    if ! shellcheck "$script"; then
12        echo "ShellCheck failed on $script"
13        exit 1
14    fi
15done

 1name: ShellCheck
 2
 3on: [push, pull_request]
 4
 5jobs:
 6  shellcheck:
 7    runs-on: ubuntu-latest
 8
 9    steps:
10      - uses: actions/checkout@v3
11
12      - name: Run ShellCheck
13        run: |
14          sudo apt-get install shellcheck
15          find . -type f -name "*.sh" -exec shellcheck {} \;

1shellcheck:
2  stage: lint
3  image: koalaman/shellcheck-alpine
4  script:
5    - find . -type f -name "*.sh" -exec shellcheck {} \;
6  allow_failure: false

 1#!/bin/bash
 2
 3# Disable warning for entire line
 4# shellcheck disable=SC2086
 5for file in $(ls -la); do
 6    echo "$file"
 7done
 8
 9# Disable for entire script
10# shellcheck disable=SC1091,SC2119
11
12# Disable multiple warnings (format varies)
13command_that_fails() {
14    # shellcheck disable=SC2015
15    [ -f "$1" ] && echo "found" || echo "not found"
16}
17
18# Disable specific check for source directive
19# shellcheck source=./helper.sh
20source helper.sh

1# Problem
2for i in $list; do done
3
4# Solution
5for i in $list; do done  # If $list is already quoted, or
6for i in "${list[@]}"; do done  # If list is an array

 1# Problem
 2some_command
 3if [ $? -eq 0 ]; then
 4    echo "success"
 5fi
 6
 7# Solution
 8if some_command; then
 9    echo "success"
10fi

1# Problem
2[ -f "$file" ] && echo "exists" || echo "not found"
3
4# Solution - clearer intent
5if [ -f "$file" ]; then
6    echo "exists"
7else
8    echo "not found"
9fi

1# Problem
2echo 'Variable value: $VAR'
3
4# Solution
5echo "Variable value: $VAR"

1# Problem
2ps aux | grep -v grep | grep myprocess
3
4# Solution
5pgrep -f myprocess

 1#!/bin/bash
 2
 3# Sequential checking
 4for script in *.sh; do
 5    shellcheck "$script"
 6done
 7
 8# Parallel checking (faster)
 9find . -name "*.sh" -print0 | \
10    xargs -0 -P 4 -n 1 shellcheck

 1#!/bin/bash
 2
 3CACHE_DIR=".shellcheck_cache"
 4mkdir -p "$CACHE_DIR"
 5
 6check_script() {
 7    local script="$1"
 8    local hash
 9    local cache_file
10
11    hash=$(sha256sum "$script" | cut -d' ' -f1)
12    cache_file="$CACHE_DIR/$hash"
13
14    if [[ ! -f "$cache_file" ]]; then
15        if shellcheck "$script" > "$cache_file" 2>&1; then
16            touch "$cache_file.ok"
17        else
18            return 1
19        fi
20    fi
21
22    [[ -f "$cache_file.ok" ]]
23}
24
25find . -name "*.sh" | while read -r script; do
26    check_script "$script" || exit 1
27done

1shellcheck script.sh
2
3# Output:
4# script.sh:1:3: warning: foo is referenced but not assigned. [SC2154]

1shellcheck --format=gcc script.sh
2
3# Output:
4# script.sh:1:3: warning: foo is referenced but not assigned.

1shellcheck --format=json script.sh
2
3# Output:
4# [{"file": "script.sh", "line": 1, "column": 3, "level": "warning", "code": 2154, "message": "..."}]

1shellcheck --format=quiet script.sh
2
3# Returns non-zero if issues found, no output otherwise