Professional and Affordable Web Design

0800 080 5401

Refactoring code with find, xargs and sed

GNU/Linux comes with some fantastic tools, most of which are very specific in what they do, however when joined together they can form a very powerful workflow. The tools I join together on a daily basis are xargs, sed and find.

I'll go over each of these separately first, then talk about joining them together to mass edit many files, something which is needed a lot when programming. In the example, we'll aim to change the name of the class 'FooException' to 'BarException'.


Find is a tool that searches for files in a given directory (recursively as well), and is where our tool set starts. There are many configuration options for Find, however I shall just go over some basics that are enough for the usage we need. A full indepth manual for Find can be found in the 'find' man page.

To start, we'll find all files within a specified directory:

find ./dir/ -type f

This should now display all files within the './dir' directory and all sub folders (recursively). '-type f' controls what should be found, in the case the 'f' stands for 'files'. When we are wanting to mass edit PHP files though, we'll want to make sure we get just PHP files and not every single file. Find supports the '-name' argument which lets us do this easily:

find ./dir -name “*.php”

Sometimes you will only want to search within a directory and not the sub folders, this can be achieved by using the '-maxdepth' argument, such as :

find ./dir -maxdepth 1 -name “*.php”


xargs lets us build and execute commands from the standard input, and will let us link up a few command easily. While xargs is not actually required for what we are aiming at doing, I find it easier and quicker to use than just the 'find' tool.

I wont go into depth with xargs, since we'll only be using it at the very basic level. In the below example, we'll take the input from the last above 'find' command, and use it with 'xargs' and 'echo' to change the output:

find ./dir -maxdepth 1 -name “*.php” | xargs echo “foo”

Each file that 'find' found, should now be prefixed with 'foo'.


sed is a Stream EDitor which allows us to performance text transformations using regex. This tool will give us the magic in mass text replacement to rename our classes. Below is a very basic example of using sed to transform text:

echo “foo” | sed 's/f/b/g'

This will output 'boo'. What happens here is sed is finding all occurrences of 'f' and replacing them with 'b', resulting in 'foo' becoming 'boo'. Learning regular expressions is outside of the scope or this article, and I am going to assume you have knowledge of it.

Linking them all up

So now we want to change the name of a class in our PHP application, 'FooException' to 'BarException'. You could go around every single file, and change them manually – however for a big application that could take a very long time. Instead we shall use the tools above to do it for us in seconds:

find ./dir -name “*.php” | xargs sed -i 's/FooException/BarException/gi'

The '-i' argument we pass to 'sed' tells it to edit the file in place, without it the file would not be edited, there are also 2 regular expression modifiers that I use, 'g' and 'i'. The first one, 'g' tells it to replace all occurrences of it in a single line, without it if there are multiple 'FooException' strings on one line, only the first will be replaced. The latter, 'i' makes it case-insensitive, meaning it will match for 'fooexception', 'fooExCeption' etc.

That is all there is to it. Changing a class name over for an entire application is something that can be done in seconds thanks to the above tools. Of course you can do more major changes to your code, but this is purely an example of what can be done.

Comments0 Comments

All comments are moderated for spam and will not be shown. All genuine comments wil be show, however the links will be based on a NO FOLLOW RULE. Repeat commenters adding value to the articles and discusions will have removed alowing Follow Rule to Work.

Make a Comment

Notify me when someone responds

Quick Contact

See Full Portfolio Some Of Our Work

Screenshot of website

Driving Schools Booking Service (DSBS) is a network of driving instructors, covering the whole of the UK. For this project, we were...

Screenshot of website

County Security is a fully featured E - commerce solution, with an integrated "system configurator", which allows users to choose...

Customer News & Resources

At Mutiny Design we are constantly gathering together articles and help guides to assist our clients.

Introduction to sitemap.xml

Checking for a sitemap A site map (or sitemap) is a list of pages of a web site accessible to crawlers or users. It can be either a document in any form used as a planning tool for web design, or a web page that lists the pages on a web site, Some developers feel that site index is a more appropriately used term to relay page function, web visitors are used to seeing each term and generally associate both as one and the same. However, a site index is often an A-Z index that provides access to content, while a site map provides a general... Read More »

Center a web page in CSS

One simple way to center a web page using CSS is to create a container div, that is horizontally centered by having its left and right margins set to auto. Using this method, you can still apply colours / background images to the body tag, so its a flexible solution. (if you didnt need this ability, just apply margins and width to the body tag instead, and forget using the container div). The container div has the same width as your webpage and, well, contains it. All the code for your web page is placed inside the container div. This will... Read More »