How do I search code with grep?

Searching through a codebase can feel slow when you rely only on your editor’s global search. grep gives you a direct, script-friendly way to find patterns across files and folders from the terminal. It’s quick, flexible, and works well for everything from spotting function calls to hunting down configuration values.

What is grep and when should you use it?

grep searches text input for lines that match a pattern. In practice, that means you can scan source files, logs, or generated output for:

Function or method names (handleRequest, to_json, render)
Error strings ("connection refused", "timeout")
TODO or FIXME notes
Imports and module usage
Config keys (API_KEY, timeout_ms, feature_flag)

It shines when you need repeatable searches, want results you can pipe to other commands, or need to scan large folder trees quickly.

The basic grep pattern

The simplest form is:

bash

1grep "pattern" file

Example:

bash

1grep "TODO" app.py

This prints every line in app.py that contains TODO.

If you want line numbers:

bash

1grep -n "TODO" app.py

If you want the filename included (useful when searching multiple files):

bash

1grep -H "TODO" app.py

Searching recursively through a project

Most code searches are recursive:

bash

1grep -R "pattern" .

Example: find where handleLogin is used:

bash

1grep -R "handleLogin" .

To include line numbers and show filenames clearly:

bash

1grep -RIn "handleLogin" .

Common flags here:

-R recursive
-I skip binary files
-n show line numbers

Case-insensitive searches and whole words

To ignore case:

bash

1grep -Ri "error" .

To match whole words only (so cat doesn’t match concatenate):

bash

1grep -Rw "cat" .

These help reduce noisy matches in large repositories.

Using regular expressions for smarter matching

grep supports regular expressions. Two common modes:

Basic regex (default)
Extended regex with -E (often easier)

Example: find import statements for either requests or httpx:

bash

1grep -REn "import (requests|httpx)" .

Example: find function definitions in Python (simple pattern):

bash

1grep -REn "^def [a-zA-Z_][a-zA-Z0-9_]*" .

Example: find lines that end with a semicolon (useful in mixed code or generated files):

bash

1grep -REn ";$" .

Showing context around matches

Sometimes the matching line isn’t enough. Add context:

-C N shows N lines before and after
-B N shows N lines before
-A N shows N lines after

Example: show 3 lines around matches for deprecated:

bash

1grep -RIn -C 3 "deprecated" .

This is handy for reading surrounding logic without opening a file.

Filtering by file type and excluding folders

Limit the search to certain file patterns using --include:

bash

1grep -RIn "timeout" . --include="*.js"

Exclude generated or vendor directories:

bash

1grep -RIn "timeout" . --exclude-dir=node_modules --exclude-dir=dist --exclude-dir=build

Exclude files by name pattern:

bash

1grep -RIn "timeout" . --exclude="*.min.js"

This keeps results focused and avoids scanning large dependency trees.

Inverting matches and counting results

To show lines that do not match a pattern:

bash

1grep -RIn -v "DEBUG" .

To count matches per file:

bash

1grep -RIn -c "TODO" .

To list only filenames that contain the match:

bash

1grep -RIl "TODO" .

To list filenames that do not contain the match:

bash

1grep -RIL "TODO" .

Practical workflows for code search

A few reliable day-to-day searches:

Find hardcoded secrets (then verify before acting):
bash
```
1grep -RIn "API_KEY" . --exclude-dir=node_modules
```
Locate old endpoints or routes:
bash
```
1grep -RIn "/v1/" .
```
Find usage of a class or symbol:
bash
```
1grep -RInw "UserService" .
```
Review all TODOs in only source folders:
bash
```
1grep -RIn "TODO" src tests
```

Closing thoughts

grep is a strong tool for code search because it’s predictable: you can refine patterns, limit scope, add context, and combine it with other command-line tools. Once you get comfortable with recursive searches, file filtering, and regex, it becomes a natural part of reading and maintaining code.