Search file contents in multiple directories with Recursive grep

There are times – many in fact – when I need to find a file, or multiple files containing a particular string. For example, I’m developing a web application, and need to find out which pages call a particular class method, say, all the files which call the getTopTenCDs() method – I can do this by opening a Terminal, and running grep (Global Regular Expression Print), with a couple of options:

grep -r -n 'getTopTenCDs()' /var/www/cdcollection/*

This will return a list of files, and the lines within those files, and the line numbers containing the string ‘getTopTenCDs()’ in the directory /var/www/cdcollection/. The -n option tells grep to output the line numbers, the -r option tells grep to search recursively through the sub-directories too, and * tells it to look in all files – which can be changed to *.php etc: /var/www/cdcollection/*.php

So, the output would be something along the lines of:

/var/www/cdcollection/viewcd.php:192:   $topTen = $cd->getTopTenCDs();
/var/www/cdcollection/sidebar.php:215:   $topTen = $cd->getTopTenCDs();

If I just want a list of files without the lines containing the search string, I can use the -l option:

grep -r -l 'getTopTenCDs()' /var/www/cdcollection/*

which would simply return:

/var/www/cdcollection/viewcd.php
/var/www/cdcollection/sidebar.php

As the name implies, grep uses Regular Expressions, and therefore the search string can contain the usual RegEx operatiors: . ? * + {n} etc. RegEx is out of scope for this post I’m affraid – there are dozens of great tutorials available on RegEx, and applying RegEx to grep.

One final point about grep: if the search string begins with a hyphen (minus sign, or whatever you want to call “-”), the search string needs to be preceded with the -e option:

grep -r -e '-starts with a hyphen' /var/www/cdcollection/*

so that grep doesn’t mistake the search pattern for an option! Forget the -e option, and you’ll get:

grep: invalid option -- $
Usage: grep [OPTION]... PATTERN [FILE]...
Try `grep --help' for more information.

Also, remember the ever useful pipe | and output to file > commands. If the list printed by grep is huge, you can simply pipe it to more:

grep -r 'getTopTenCDs()' /var/www/cdcollection/* | more

or, if you want to save it to a file to peruse later:

grep -r 'getTopTenCDs()' /var/www/cdcollection/* > ~/grep_output.txt

Always useful.

Finally, remember to take a look at the grep man page:

man grep

Which contains a world of useful information, including a wealth of options I haven’t covered.

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