Linux Basic — ShellCheck Compliance
ShellCheck Compliance
ShellCheck is the static analyser every shell script should pass. It catches quoting bugs, unset vars, bad globs, and 200+ other issues before runtime.
Install & Run
# macOS
brew install shellcheck
# Ubuntu/Debian
apt install shellcheck
# run on a script
shellcheck script.sh
Common Warnings & Fixes
SC2086: Quote to prevent word splitting
# BAD
echo $var
# GOOD
echo "$var"
Always quote variables unless you explicitly want splitting.
SC2046: Quote to prevent word splitting in $(...)
# BAD
files=$(ls *.txt)
# GOOD
mapfile -t files < <(ls *.txt)
# or just use globs:
files=(*.txt)
SC2155: Declare and assign separately
# BAD — exit code of cmd is lost
local result=$(some_command)
# GOOD
local result
result=$(some_command) || die "command failed"
SC2164: cd can fail — use cd ... || exit
# BAD
cd /some/dir
# GOOD
cd /some/dir || exit 1
Or use set -e so the script exits automatically.
SC2128: Expanding an array without an index
# BAD
files=("a" "b")
echo "$files" # only prints first element
# GOOD
echo "${files[@]}" # all elements
Disabling Checks (Rarely Needed)
If ShellCheck flags something intentional, disable it with a comment explaining why:
# shellcheck disable=SC2086
# word-splitting is intentional here for xargs
xargs cmd $opts
Disable per-line, not globally, and always add a reason.
CI Integration
Add to your CI pipeline:
# .github/workflows/lint.yml
- name: ShellCheck
run: shellcheck **/*.sh
Fail the build on any warning.
Levels of Compliance
| Level | Description |
|---|---|
| None | no warnings about critical bugs (quoting, unset vars) |
| Style | no style warnings (use [[ over [, etc.) |
| Pedantic | enable all checks including style nitpicks |
Aim for zero warnings at default level. Pedantic is optional.
ShellCheck + set -euo pipefail
ShellCheck’s warnings overlap with strict mode. Use both:
set -euo pipefail # runtime safety
# ShellCheck catches the issues that slip past -e/-u
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