Lập Trình Linux

Linux Terminal Basics: Grep

Grep can be used for finding text within a file or output from previous command. You can use Regex with grep (or egrep), which I cover in this video.

Bash Regex Cheatsheet:

Background from Charlie Henson:
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  • You can also return the lines around the matching line.
    grep -A3 pattern filename will include the 3 lines after the match.
    grep -B4 " " to include 4 lines before the match.
    grep -C2 " " to include 2 lines before and 2 lines after the match.

  • Knowing Grep turns you from a competent IT guy into a full on hacker. Just need a black hoodie.

  • very helpful n precise. Sounds UK or Australian accent.

  • instead of:

    $ ps -a | grep [[:space:]][[:digit:]][[:space:]]

    can't you just do:

    $ ps -a | egrep ' [0-9] '

    or does that not always work?

  • If in a script and it's not huge file (or otherwise, performance isn't an issue), I always opt for a pure-shell appraoch in my programs, both personal and published on GitHub. For example, here I'm getting the currently used RAM, using just the two processes (bash and free):

    while read -a X; do
    if [ "${X[0]}" == "Mem:" ]; then
    printf "%-'dMn" "${X[2]}"
    done <<< "$(/usr/bin/free -m)"

    Whereas most people would wind up using bash, free, grep, cut, and God knows what else; I consider this massively inefficient and messy. That said, it really does depend on the task, and obviously this is more advanced than a simple grep and cut, but thought I'd still show passers-by my approach.

  • Noice.

  • I have to just take a moment to say how much I am loving this series. I love learning new things about commands I already knew, and new CLI commands, that can help me in my daily tasks

  • Please do a tutorial about cmatrix, sl, ddate and xlogo.

  • DavidDavid

    Author Reply


  • GNU grep v. BSD grep feels like a missing section of this video. People using a Mac will in some instances have a much different experience without first installing core utils through some 3rd party source. I remember finding that out when I tried `grep -i…` in OS X years ago.

  • Worth mentioning : -F to search for non regex strings (faster when handling huge files)

  • Why do you hide the window decorations you present on ? I noticed that in your recent videos. Still on KDE Neon ?

  • Using grep -rn is a real life saver for coders, especially within a large codebase. I've been using it for years.