A large collection of Unix/Linux ‘grep’ command examples

Linux grep commands FAQ: Can you share some Linux/Unix grep command examples?

Sure. The name grep means "general regular expression parser", but you can think of the grep command as a "search" command for Unix and Linux systems: it's used to search for text strings and more-complicated "regular expressions" within one or more files.

I think it's easiest to learn how to use the grep command by showing examples, so let's dive right in.

Linux: Recursive file searching with grep -r (like grep + find)

Linux grep FAQ: How can I perform a recursive search with the grep command in Linux?

Solution: find + grep

For years I always used variations of the following Linux find and grep commands to recursively search subdirectories for files that match a grep pattern:

find . -type f -exec grep -l 'alvin' {} \;

This command can be read as, “Search all files in all subdirectories of the current directory for the string ‘alvin’, and print the filenames that contain this pattern.” It’s an extremely powerful approach for recursively searching files in all subdirectories that match the pattern I specify.

A Linux shell script to find large files

I made a mistake in configuring logrotate on a new Linux system, and almost ran into a problem because of that. Fortunately I saw the problem before it became a BIG problem, but as a result, I decided to add a script to my Linux system to check for large files, typically log files that have grown out of control for one reason or another.

Here then is a simple Linux shell script I named, which searches the filesystem for files that are larger than 1GB in size:

A Linux shell script to rename files with a counter and copy them

As a brief note today, I was recently looking for all Messages/iMessage files that are stored on my Mac, and I used this shell script to copy all of those files — many of which have the same name — into a directory named tmpdir, giving them all new names during the copy process:

for i in `cat myfiles`
    fname=`basename $i`
    cp $i tmpdir/${count}-${fname}
    count=`expr $count + 1`

Scala: How to extract parts of a String that match regex patterns

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 1.9, “Extracting Parts of a String that Match Patterns.”


You want to extract one or more parts of a Scala String that match the regular-expression patterns you specify.


Define the regular-expression (regex) patterns you want to extract, placing parentheses around them so you can extract them as “regular-expression groups.” First, define the desired pattern:

How to find regex patterns in Scala strings

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 1.7, “Finding Patterns in Scala Strings.”


You need to determine whether a Scala String contains a regular expression pattern.

How to search multiple jar files for a string or pattern (shell script)

Here’s a Unix shell script that I use to search Java Jar files for any type of string pattern. You can use it to search for the name of a class, the name of a package, or any other string/pattern that will show up if you manually ran jar tvf on each jar file. The advantage of this script — if you’re a Unix, Linux, or Cygwin user — is that it will search through all jar files in the current directory: