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Questions tagged [grep]

grep is a command-line text-search utility originally written for Unix. It uses regular expressions to match text, and is commonly used as a filter in pipelines. Use this tag only if your question relates to programming using grep or grep-based APIs. Questions relating to using or troubleshooting grep command-line options itself are off-topic.

Grep

The name comes from and similar editors, and is derived from global / regular expression / print.

Grep is a command-line utility for searching plain-text data sets for lines matching a regular expression. Grep was originally developed for the Unix operating system, but is available today for all Unix-like systems.

There are many programming languages which include a command or statement called grep; please simply use that language's tag for questions which do not pertain to the Unix utility.

Variations

The following are the several implementations of grep available in some Unix environments:

  • : same as grep -E - Interprets the pattern as an extended regular expression.
  • : same as grep -F - Interprets the pattern as a list of fixed strings, separated by newlines, any of which is to be matched.
  • : displays the processes whose names match a given regular expression.

Common options

  • -f file - Obtain patterns from file, one per line.
  • -i - Ignore case distinctions in both the pattern and the input files.
  • -o - Show only the part of a matching line that matches the pattern.
  • -c - Print a count of matching lines for each input file.
  • -R - Read all files under each directory recursively.
  • -v - Invert the sense of matching to select non-matching lines.

Frequently asked

Other Stack Exchange sites

References

  1. grep/egrep/fgrep man page
  2. pgrep man page
  3. POSIX grep man page
  4. GNU grep manual

Books

  • grep Pocket Reference - "A quick pocket reference for a utility every Unix user needs"
  • GNU GREP and RIPGREP - Step by step guide with hundreds of examples and exercises. Includes detailed discussion on BRE/ERE/PCRE(2)/Rust regular expressions used in these commands.
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Colorized grep -- viewing the entire file with highlighted matches

I find grep's --color=always flag to be tremendously useful. However, grep only prints lines with matches (unless you ask for context lines). Given that each line it prints has a match, the highlighting doesn't add as much capability as it…
zslayton
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Delete all local git branches

I follow a development process where I create a new local branch for every new feature or story card. When finished I merge the branch into master and then push. What tends to happen over time due to a combination of laziness or forgetfulness, is…
Louth
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How can I exclude one word with grep?

I need something like: grep ^"unwanted_word"XXXXXXXX
john
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grep a tab in UNIX

How do I grep tab (\t) in files on the Unix platform?
Sachin
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Grep only the first match and stop

I'm searching a directory recursively using grep with the following arguments hoping to only return the first match. Unfortunately, it returns more than one -- in-fact two the last time I looked. It seems like I have too many arguments, especially…
Tim Kamm
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Capturing Groups From a Grep RegEx

I've got this script in sh (macOS 10.6) to look through an array of files: files="*.jpg" for f in $files do echo $f | grep -oEi '[0-9]+_([a-z]+)_[0-9a-z]*' name=$? echo $name done So far $name merely holds 0, 1 or 2,…
Isaac
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How can I grep for a string that begins with a dash/hyphen?

I want to grep for the string that starts with a dash/hyphen, like -X, in a file, but it's confusing this as a command line argument. I've tried: grep "-X" grep \-X grep '-X'
Mike
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How can I make grep print the lines below and above each matching line?

I want to search each line for the word FAILED, then print the line above and below each matching line, as well as the matching line. Input: id : 15 Status : SUCCESS Message : no problem id : 15 Status : FAILED Message : connection error Desired…
poiuytrez
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Get line number while using grep

I am using grep recursive to search files for a string, and all the matched files and the lines containing that string are print on the terminal. But is it possible to get the line numbers of those lines too?? ex: presently what I get is…
sai
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How can I format my grep output to show line numbers at the end of the line, and also the hit count?

I'm using grep to match string in a file. Here is an example file: example one, example two null, example three, example four null, grep -i null myfile.txt returns example two null, example four null, How can I return matched lines together with…
London
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How do I grep for all non-ASCII characters?

I have several very large XML files and I'm trying to find the lines that contain non-ASCII characters. I've tried the following: grep -e "[\x{00FF}-\x{FFFF}]" file.xml But this returns every line in the file, regardless of whether the line…
pconrey
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How to check if a file contains a specific string using Bash

I want to check if a file contains a specific string or not in bash. I used this script, but it doesn't work: if [[ 'grep 'SomeString' $File' ]];then # Some Actions fi What's wrong in my code?
Hakim
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Fast way of finding lines in one file that are not in another?

I have two large files (sets of filenames). Roughly 30.000 lines in each file. I am trying to find a fast way of finding lines in file1 that are not present in file2. For example, if this is file1: line1 line2 line3 And this is…
Niels2000
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How to perform grep operation on all files in a directory?

Working with xenserver, and I want to perform a command on each file that is in a directory, grepping some stuff out of the output of the command and appending it in a file. I'm clear on the command I want to use and how to grep out string(s) as…
user2147075
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How to search and replace using grep

I need to recursively search for a specified string within all files and subdirectories within a directory and replace this string with another string. I know that the command to find it might look like this: grep 'string_to_find' -r ./* But how…
billtian
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