Leveraging the Linux grep Command for Web Development

Although the Linux command line can seem intimidating at times, it holds the power to greatly improve our productivity as web developers. In this article, I cover one of my all-time favorite Linux commands - the grep utility.

Using grep to Search for Strings

The grep command lets users find strings in files. Computer scientist Ken Thompson (who also helped create the Golang programming language), originally authored the grep utility in 1973, and grep continues to be an integral part of Unix operating systems today. Its basic usage is like this

grep someWord someFile.txt

The above command searches inside someFile.txt for all occurrences of the word "someWord". The grep command will then print each line where a match for "someWord" was found to the terminal. In this example, grep is case sensitive. Therefore, "sOmEword" and "someword" will not be matches. To get a case-insensitive match, we can add in the -i flag like this

grep -i someWord someFile.txt

and this can sometimes come in handy.

Why I Love grep

So why is grep useful to us as developers you might ask? The grep command can be helpful for both working in our own projects, and in someone else's codebase.

For example, in web development, I frequently write out JavaScript console.log statements to check the expected behavior of variables. Although I usually remove these when I'm done testing something, before deploying an application, I like to double check that I have not left any console.log statements in any of my files. To do this, I use the following grep command from the main directory of the project I'm working on:

grep -rl 'console.log' --exclude-dir=node_modules ./*

This grep command recursively (via the r flag) searches all files below the current working directory for "console.log", and prints to the terminal a list (using the l flag) of all files that contain a match. Pretty cool, right? But what if in addition to node_modules, you also don't want to search in .git and .cache? You can just add those in brackets to form a glob with the exclude flag like this

grep -rl 'console.log' --exclude-dir={node_modules,.git,.cache} ./*

Then grep will also not search in the .git and .cache folders.

While the above examples focus on how we might use grep in searching for a console.log statement, I've found grep to be incredibly useful when learning a new codebase to see where some function is being used, tracking down software bugs based on an error message, and finding files using a string that needs to be renamed during a code refactor. This last example in particular lays the framework on how grep can be combined with another powerful Linux command - the sed utility, which I intend to discuss in a future article.