Beginner's Guide to grep

Did you know the whole grep program was written within a day, by non other then Ken Thompson https://youtube.com/watch?v=NTfOnGZUZDk&feature=share7

This is cool, but I'd love to see some examples outputs so I can get a sense of what it actually does.

Very nice guide, thanks for taking the time!

Good information and barely scratches the surface of grep usage. It can get a lot more complicated but also do a lot more than you think.

Two of my most used grep invocations are:

• Diff two files, showing lines: grep -xvFf (file2) (file1)
• Show lines that do not contain a string: grep -rivE '^#' (file) ( only shows uncommented lines for most Linux configuration files)

You can live without vim, but not without cat and grep.

Excellent guide, thanks for the write up!

One thing I'd like to point out is that you can pipe output from an application into grep and then be able to use all the information above.

For instance if I want to know the full name of my wireguard interface I can just pass (pipe) the output of ifconfig into grep:

ifconfig | grep wire

Others have already mentioned man grep or grep help

But, in case you don't know about it, there are two great utilities to get examples and help for almost any given command: tldr and cheat are great.

https://github.com/cheat/cheat

https://github.com/tldr-pages/tldr

Just cheat grep or tldr grep and you're good to go :)

A few more options that I use pretty much daily:

• -v for reversing the match (display non-matching instead of matching)
• -e to specify multiple patterns, matching any one is sufficient
• -w to match only at word boundaries, easier to type than the equivalent regexp
• -c for displaying the match count rather than the matches

And some that that I use occasionally:

• -NUM, -B NUM, -A NUM also show NUM lines around/before/after match
• -l to display only the filenames with the matches
• -F "fixed" pattern meaning literal match only rather than regexp. Great to avoid having to quote regexp special characters when you don't need regexp matching
• -P for PCRE style regexps
• -f to read match patterns from a file
• -q quiet, only produce exit status, no output. Useful in shell expressions (scripts, one liners).
• -a force treating the input as text (useful to override the binary detection heuristic. mnemonic: ascii)

Beginner’s Guide to grep

man grep

Would you mind explaining this regular expression a little, and how it's grabbing email addresses? What is "\b"? What does "+" do? And the {2,}?

Also see https://pubs.opengroup.org/...

Fantastic summary of one of the most universally used cli tool. One thing to add is that the name grep comes from the ed command g/re/p which stands for "global, regular expression, print" since thats what it does; search everything (global) for a given regular expression (even if the "regular expression" is just a specific string to match) and prints it out. Keeping the name origin in mind helps me to remember what it does.

Thank you, always fun to read these and learn about an option you haven't used yourself yet.

If you are serious about working in a terminal, then I highly recommend learning modern replacements for the old tools.

In this case ripgrep (or rg) https://github.com/BurntSushi/ripgrep is phenomenal. Especially for searching recursively in a large directory tree it is unbelievably quicker than regular grep.

It won't be installed on any random machine, so grep is still useful, but if you regularly need to text search in files then there are better tools.

Though related, it's often conflated with regular expressions as a concept. On that note, services like RegExr let you test patterns and their effects visually.

grep -v inverts the search. All lines that do not match are printed.

"Using regular expressions" is misleading. A beginner could think that by default grep is looking for a literal string, but it does not.

Bookmarked for later, thank you kind lemming.