I needed to review a large number of text files and pick those that included a string pattern. grep is awesome for this.
I opened a terminal and navigated to the main directory folder where I had several subfolders and susbsequent sub-folders. There, I run a grep command and wrote the output in a .txt file.
~/mainFolder$ grep -H -r 'stringPattern' ~/mainFolder/ > ~/myTextFile.txt
The basic structure of the command is:
grep [options] [regexp] [filename]
From https://en.wikipedia.org/wiki/Grep, grep stands for “g/re/p (globally search for a regular expression and print matching lines)” and it’s a command-line programme.
The options I used are:
-H, which commands to print out the filename for each match. This is key as this will allow me to locate those files! And-r, which sets the grep to be recursive, searching within sub-folders.
The regexp can be any regex, in my case, I used the literal string that I wanted to search, say ' 5', the number five.
The filename in this case is every file in the folder and sub-folders.
Finally, > is an extra that I added in order to write the output in a file, instead of returning it as standard output. For reference https://askubuntu.com/a/420983.
I used this as reference: “A Beginner’s Guide To Grep: Basics And Regular Expressions” in https://www.opensourceforu.com/2012/06/beginners-guide-gnu-grep-basics/. Also, see https://www.howtoforge.com/tutorial/linux-grep-command/.