Creating custom hook scripts in Git - Quick Revision & Summary

Recall & Review

beginner

What is a Git hook?

A Git hook is a script that Git runs before or after events like commits, pushes, or merges. It helps automate tasks.

beginner

Where do you place custom Git hook scripts?

Custom Git hook scripts go inside the .git/hooks folder of your repository.

beginner

How do you make a Git hook script executable?

You run chmod +x <hook-script> to make the script executable so Git can run it.

beginner

Name two common Git hook types you can customize.

Two common hooks are pre-commit (runs before a commit) and post-commit (runs after a commit).

intermediate

What happens if a pre-commit hook script exits with a non-zero status?

Git stops the commit process and shows an error. This lets you prevent bad commits.

Where should you place a custom Git hook script?

A root folder of the project

B .git/hooks folder

C any folder in your home directory

D inside the .gitignore file

Git looks for hook scripts inside the .git/hooks folder of the repository.

What command makes a Git hook script executable?

A chmod 777 <hook-script>

B git hook enable <hook-script>

C chmod +x <hook-script>

D git run-hook <hook-script>

chmod +x sets the executable permission needed for Git to run the hook script.

Which hook runs before a commit is finalized?

A post-merge

B post-commit

C pre-push

D pre-commit

The pre-commit hook runs before the commit is saved, allowing checks or validations.

What happens if a pre-commit hook script returns a non-zero exit code?

A The commit is stopped

B The commit proceeds normally

C Git deletes the commit

D Git ignores the hook

A non-zero exit code signals failure, so Git stops the commit to prevent errors.

Which language can you use to write Git hook scripts?

A Any scripting language like Bash, Python, or Perl

B Only Git's own language

C Only compiled languages like C

D Only JavaScript

Git hooks are scripts and can be written in any language your system can run.

Explain how to create and enable a custom pre-commit Git hook script.

Think about where the script goes and how Git runs it.

Describe what happens when a Git hook script fails during a commit.

Focus on the effect of the script's exit code.

Practice

1. What is the main purpose of creating a custom Git hook script?

easy

A. To delete branches remotely

B. To change the Git commit message manually

C. To create new Git repositories

D. To run scripts automatically at specific Git events

Solution

1. Step 1: Understand Git hooks

   Git hooks are scripts that run automatically at certain points in Git's workflow, like before a commit or after a push.

2. Step 2: Identify the purpose of custom hooks

   Custom hooks let you automate tasks or enforce rules during these Git events without manual intervention.

3. Final Answer:

   To run scripts automatically at specific Git events -> Option D

4. Quick Check:

   Git hooks = automatic scripts at Git events [OK]

Hint: Hooks run scripts automatically at Git events [OK]

Common Mistakes:

• Thinking hooks manually change commit messages
• Confusing hooks with branch deletion
• Assuming hooks create repositories

2. Which of the following is the correct way to make a Git hook script executable on Linux or macOS?

easy

A. chmod +x .git/hooks/pre-commit

B. git hook enable pre-commit

C. chmod 777 .git/hooks/pre-commit

D. git config hook.pre-commit true

Solution

1. Step 1: Understand file permissions for hooks

   Git hooks must be executable files to run automatically.

2. Step 2: Use the correct command to make a file executable

   The command chmod +x adds execute permission without changing other permissions.

3. Final Answer:

   chmod +x .git/hooks/pre-commit -> Option A

4. Quick Check:

   Make hook executable = chmod +x [OK]

Hint: Use chmod +x to make hook scripts executable [OK]

Common Mistakes:

• Using git commands that don't exist for hooks
• Setting overly permissive permissions like 777
• Trying to enable hooks via git config

3. Given this pre-commit hook script placed in .git/hooks/pre-commit and made executable:

#!/bin/sh
if git diff --cached --quiet; then
  echo "No changes staged for commit."
  exit 1
fi

What happens when you try to commit without staging any changes?

medium

A. The commit is blocked with message 'No changes staged for commit.'

B. The commit proceeds normally without any message

C. The commit is blocked with a syntax error

D. The commit proceeds but shows a warning

Solution

1. Step 1: Analyze the script logic

   The script checks if there are no staged changes using git diff --cached --quiet. If true, it prints a message and exits with code 1.

2. Step 2: Understand Git hook exit codes

   Exiting with code 1 in a pre-commit hook stops the commit process and shows the message.

3. Final Answer:

   The commit is blocked with message 'No changes staged for commit.' -> Option A

4. Quick Check:

   Exit 1 in pre-commit = block commit [OK]

Hint: Exit non-zero in pre-commit stops commit [OK]

Common Mistakes:

• Assuming commit proceeds despite exit 1
• Confusing staged vs unstaged changes
• Expecting syntax errors from correct shell script

4. You wrote this post-commit hook script but it does not run after commits:

#!/bin/sh
echo "Commit done!"

Which is the most likely reason?

medium

A. The script filename is incorrect

B. The script is not executable

C. Git hooks cannot echo messages

D. The script must be in the project root, not .git/hooks

Solution

1. Step 1: Check common hook issues

   Hooks must be executable files inside .git/hooks/ with correct names.

2. Step 2: Identify the most common cause

   Often, scripts don't run because they lack execute permission, even if named correctly.

3. Final Answer:

   The script is not executable -> Option B

4. Quick Check:

   Hooks must be executable to run [OK]

Hint: Make hook scripts executable with chmod +x [OK]

Common Mistakes:

• Placing scripts outside .git/hooks directory
• Assuming echo is not allowed in hooks
• Using wrong hook filenames

5. You want to create a custom Git hook that prevents commits if the commit message does not contain the word 'JIRA'. Which script placed in .git/hooks/commit-msg will achieve this?

hard

A. #!/bin/sh
if grep -q 'JIRA' "$1"; then
exit 1
fi

B. #!/bin/sh
grep 'JIRA' "$1" || echo "Commit message missing JIRA"

C. #!/bin/sh
if ! grep -q 'JIRA' "$1"; then
echo "Commit message must include 'JIRA'."
exit 1
fi

D. #!/bin/sh
echo "Checking commit message for JIRA"

Solution

1. Step 1: Understand commit-msg hook argument

   The commit message file path is passed as the first argument ($1) to the script.

2. Step 2: Check script logic for enforcing 'JIRA'

   #!/bin/sh if ! grep -q 'JIRA' "$1"; then echo "Commit message must include 'JIRA'." exit 1 fi uses grep -q to check if 'JIRA' is missing, then prints a message and exits with 1 to block the commit.

3. Step 3: Evaluate other options

   #!/bin/sh grep 'JIRA' "$1" || echo "Commit message missing JIRA" only echoes but does not block commit. #!/bin/sh if grep -q 'JIRA' "$1"; then exit 1 fi blocks if 'JIRA' is present (wrong logic). #!/bin/sh echo "Checking commit message for JIRA" just echoes without checks.

4. Final Answer:

   #!/bin/sh if ! grep -q 'JIRA' "$1"; then echo "Commit message must include 'JIRA'." exit 1 fi -> Option C

5. Quick Check:

   Exit 1 if 'JIRA' missing blocks commit [OK]

Hint: Use commit-msg hook with exit 1 to block bad messages [OK]

Common Mistakes:

• Not exiting with non-zero to block commit
• Checking for presence instead of absence
• Only printing message without blocking