Lint and test a shell script with ShellCheck and Bats

Tools used

• 

  ShellCheck

  Static analysis tool that identifies syntax errors, semantic problems, and pitfalls in bash/sh shell scripts

  40.3kHaskell

• Bats-core

  TAP-compliant testing framework for Bash 3.2+ that runs test cases written as Bash functions to verify Bash scripts and other UNIX programs.

  6.3kShell

Before you start

• -A Bash or Zsh terminal on Linux or macOS
• -The listed tools installed and available on PATH

Steps

1. 1Step 1: Write a script with a quoting bug

   The argument expansion below is deliberately unquoted.

   sh

   $ trmn_guide_dir="$(mktemp -d)"
   $ cd "$trmn_guide_dir"
   $ cat > greet.sh <<'EOF'
   #!/usr/bin/env bash
   $ printf 'Hello, %s!\n' $1
   $ EOF
   $ shellcheck greet.sh

2. 2Step 2: Fix the expansion

   ShellCheck reports SC2086. Replace the script with this version, then lint it again.

   sh

   $ cat > greet.sh <<'EOF'
   #!/usr/bin/env bash
   $ printf 'Hello, %s!\n' "$1"
   $ EOF
   $ shellcheck greet.sh

3. 3Step 3: Add behavior tests

   The second test makes sure a wildcard is treated as text instead of expanding to filenames.

   sh

   $ cat > greet.bats <<'EOF'
   #!/usr/bin/env bats
   $ @test "keeps a name with a space together" {
   $   run bash "$BATS_TEST_DIRNAME/greet.sh" 'Ada Lovelace'
   $   [ "$status" -eq 0 ]
   $   [ "$output" = 'Hello, Ada Lovelace!' ]
   $ }
   $ @test "keeps a wildcard literal" {
   $   run bash "$BATS_TEST_DIRNAME/greet.sh" '*'
   $   [ "$status" -eq 0 ]
   $   [ "$output" = 'Hello, *!' ]
   $ }
   $ EOF
   $ bats --formatter tap greet.bats

   output

   1..2
   ok 1 keeps a name with a space together
   ok 2 keeps a wildcard literal

4. 4Step 4: Check the failure path

   In the temporary greet.sh only, remove the double quotes around $1 and run Bats again. The space test should fail. Restore the quoted version afterwards.