git bisect run for automated bisect - Commands & Configuration

Introduction

When you have a bug but don't know which commit caused it, git bisect run helps you find the exact commit automatically by running a test script on each step.

When you want to find the commit that introduced a bug without manually checking each commit.

When you have a test script that can tell if the bug is present or not.

When you want to save time by automating the bisect process instead of manual testing.

When you have a large number of commits and manual bisecting is too slow.

When you want to integrate bisecting into a CI/CD pipeline for automatic bug detection.

Commands

Start the bisect session to find the bad commit.

Terminal

git bisect start

Expected Output

No output (command runs silently)

Mark the current commit as bad (contains the bug).

Terminal

git bisect bad

Expected Output

No output (command runs silently)

Mark a known good commit (e.g., tag v1.0) where the bug was not present.

Terminal

git bisect good v1.0

Expected Output

No output (command runs silently)

Run the automated test script on each commit to find the first bad commit.

Terminal

git bisect run ./test_bug.sh

Expected Output

Bisecting: 3 revisions left to test after this (roughly 2 steps)

[def5678] Introduce bug

Bisecting: 1 revision left to test after this (roughly 1 step)

[abc1234] Fix some feature

def5678 is the first bad commit



Bisecting complete after 5 steps

[def5678] Introduce bug

End the bisect session and return to the original branch.

Terminal

git bisect reset

Expected Output

Previous HEAD position was def5678 Introduce bug

Switched to branch 'main'

Key Concept

If you remember nothing else, remember: git bisect run automates finding the first bad commit by running your test script on each step.

Common Mistakes

Not marking a known good commit before running git bisect run

Git needs a reference point where the bug was not present to narrow down the search.

Always mark a known good commit with git bisect good before running the automated test.

Using a test script that does not return correct exit codes

Git bisect run relies on the script's exit code: 0 means good, non-zero means bad. Wrong exit codes cause incorrect bisect results.

Ensure your test script returns 0 if the commit is good and non-zero if bad.

Not resetting bisect after finishing

The repository stays in bisect mode, which can confuse further work.

Run git bisect reset to return to the original branch and clean state.

Summary

Start bisect with git bisect start, mark bad and good commits.

Run git bisect run with a test script to automate checking commits.

Reset bisect with git bisect reset to finish and return to normal.

Practice

1. What is the main purpose of git bisect run in debugging?

easy

A. To manually mark commits as good or bad during bisect

B. To automate the process of finding the first bad commit using a test script

C. To reset the repository to the latest commit

D. To merge two branches automatically

Solution

1. Step 1: Understand the role of git bisect run

   This command automates the bisect process by running a test script on each commit to check if it is good or bad.

2. Step 2: Compare with other options

   Manual marking is done without run, resetting or merging are unrelated to bisect automation.

3. Final Answer:

   To automate the process of finding the first bad commit using a test script -> Option B

4. Quick Check:

   Automation with test script = B [OK]

Hint: Remember: git bisect run automates testing commits [OK]

Common Mistakes:

• Confusing manual bisect with automated bisect
• Thinking it resets or merges branches
• Assuming it marks commits without a script

2. Which of the following is the correct syntax to start an automated bisect with a test script named test.sh?

easy

A. git bisect start test.sh

B. git bisect automate test.sh

C. git bisect run ./test.sh

D. git bisect test ./test.sh

Solution

1. Step 1: Recall the correct command structure

   The correct syntax to run a test script during bisect is git bisect run <script>.

2. Step 2: Match options with syntax

   Only git bisect run ./test.sh matches the correct syntax with the script path ./test.sh.

3. Final Answer:

   git bisect run ./test.sh -> Option C

4. Quick Check:

   Correct syntax = D [OK]

Hint: Use git bisect run <script> to automate tests [OK]

Common Mistakes:

• Using 'start' instead of 'run'
• Omitting './' before script name
• Using incorrect verbs like 'automate' or 'test'

3. Given the following test script test.sh that exits with 1 if a file bug.txt exists, else exits 0:

#!/bin/sh
if [ -f bug.txt ]; then
  exit 1
else
  exit 0
fi

What will git bisect run ./test.sh interpret if bug.txt is present in a commit?

medium

A. The commit will be skipped

B. The commit is good

C. The bisect will stop with an error

D. The commit is bad

Solution

1. Step 1: Understand exit codes in test script

   The script exits with 1 if bug.txt exists, which means failure (bad commit).

2. Step 2: Interpret exit code in bisect context

   git bisect run treats exit code 0 as good and non-zero as bad, so exit 1 means bad commit.

3. Final Answer:

   The commit is bad -> Option D

4. Quick Check:

   Exit 1 = bad commit = A [OK]

Hint: Exit 0 means good; non-zero means bad in bisect scripts [OK]

Common Mistakes:

• Confusing exit 1 as good
• Assuming script errors stop bisect
• Thinking bisect skips commits on exit 1

4. You run git bisect run ./test.sh but it stops with the error: ./test.sh: Permission denied. What is the most likely cause?

medium

A. The test script is missing execute permission

B. The bisect command is misspelled

C. The repository is not initialized

D. The test script returns exit code 0

Solution

1. Step 1: Analyze the error message

   The error Permission denied means the shell cannot run the script, often due to missing execute permission.

2. Step 2: Check other options

   Bisect command spelling or repo initialization would cause different errors; exit code 0 does not cause this error.

3. Final Answer:

   The test script is missing execute permission -> Option A

4. Quick Check:

   Missing execute permission = A [OK]

Hint: Make script executable with chmod +x before running [OK]

Common Mistakes:

• Ignoring file permissions
• Assuming bisect command typo
• Thinking exit code causes command not found

5. You want to find the first bad commit that introduced a bug detected by a Python test script check_bug.py. The script returns exit code 0 if no bug and 1 if bug found. Which sequence of commands correctly automates bisecting?

hard

A. git bisect start; git bisect bad <bad_commit>; git bisect good <good_commit>; git bisect run python3 check_bug.py

B. git bisect start; git bisect good; git bisect bad <bad_commit>; git bisect run python3 check_bug.py

C. git bisect start; git bisect bad; git bisect good <good_commit>; git bisect run python3 check_bug.py

D. git bisect start; git bisect good <bad_commit>; git bisect bad <good_commit>; git bisect run python3 check_bug.py

Solution

1. Step 1: Understand bisect start sequence

   You must start bisect, mark a known bad commit first, then a known good commit, then run the test script.

2. Step 2: Match the correct order

   git bisect start; git bisect bad <bad_commit>; git bisect good <good_commit>; git bisect run python3 check_bug.py correctly marks bad commit first, then good commit, then runs the script with Python.

3. Final Answer:

   git bisect start; git bisect bad <bad_commit>; git bisect good <good_commit>; git bisect run python3 check_bug.py -> Option A

4. Quick Check:

   Bad then good then run script = C [OK]

Hint: Always mark bad commit first, then good, then run script [OK]

Common Mistakes:

• Swapping good and bad commit order
• Forgetting to start bisect
• Running script before marking commits