pre-push hook in Git - Time & Space Complexity

Time Complexity: pre-push hook

O(n)

Understanding Time Complexity

We want to understand how the time taken by a git pre-push hook changes as the amount of work it does grows.

Specifically, how does the hook's execution time grow when it checks many files or runs many commands before pushing?

Scenario Under Consideration

Analyze the time complexity of the following pre-push hook script.

#!/bin/sh
# pre-push hook example

while read local_ref local_sha remote_ref remote_sha ; do
   git diff --name-only $local_sha $remote_sha | while read file ; do
     echo "Checking $file"
     # simulate check command
   done
 done

This hook reads refs being pushed, then lists changed files and checks each one before allowing the push.

Identify Repeating Operations

• Primary operation: Loop over changed files to check each one.
• How many times: Once per changed file in the push.

How Execution Grows With Input

As the number of changed files increases, the hook runs more checks, so time grows roughly in direct proportion.

Input Size (n)	Approx. Operations
10 changed files	10 checks
100 changed files	100 checks
1000 changed files	1000 checks

Pattern observation: The time grows linearly with the number of changed files.

Final Time Complexity

Time Complexity: O(n)

This means the hook's running time increases directly with the number of files it checks before pushing.

Common Mistake

[X] Wrong: "The hook always runs in constant time no matter how many files change."

[OK] Correct: The hook checks each changed file one by one, so more files mean more work and longer time.

Interview Connect

Understanding how hooks scale helps you write efficient checks that keep your code safe without slowing down your workflow too much.

Self-Check

"What if the hook ran a single command that checked all files at once instead of one by one? How would the time complexity change?"