Inserting a function into all classes in a directory via Terminal

Or; Multi-line Search and Replace regular expression on the Command Line.

The situation

You have a single abstract class which is extended multiple times in 10 or 100 different classes throughout your codebase.

You’ve found a need for a new abstract method which all classes must now implement.

The problem

Who wants to manually insert that new code into all those classes!? (I don’t).

We need an automated way to do this

The solution

ack -l "extends MyClass" | xargs perl -i -pe 'BEGIN{undef $/;} s/(extends MyClass[^{]*{)/\1\r\n\r\n\tpublic function newMethod() {}\r\n\r\n/smg'

How it works

Breaking this up into its parts goes like so:

ack -l "extends MyClass"

Find all files which include the string “extends MyClass” and list them.

xargs perl -i -pe '[...]'

Do an in-place perl regular expression search and replace on each file found from above.

BEGIN{undef $/;}

Tell Perl to no longer consider end-of-line’s – this allows us to do a multi-line search and replace.


Look for all occurrences of [SEARCH] in the file and replace it with [REPLACE].


(extends MyClass[^{]*{)

Match all occurrences of the string “extends MyClass” followed by any characters up until the opening brace (“{“) (remember this also includes new lines!), so it will successfully match all of the following:

extends MyClass{

extends MyClass {

extends MyClass

extends MyClass
/* Comment about class */


\1\r\n\r\n\tpublic function newMethod() {}\r\n\r\n

“\1” will leave what was matched (in the braces “(” and “)” in the result).

“\r\n\r\n” inserts two new lines.

“\t” inserts a tab.

“public function newMethod() {}” inserts the new method.

“\r\n\r\n” inserts a further two lines

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