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--- tools:grep [2024/06/03 08:21] – Humphrey Boa-Gart
+++ tools:grep [2024/09/28 03:07] (current) – Humphrey Boa-Gart
@@ Line 1: / Line 1: @@
-{{wst>iw-cleanup}}
 ====== grep ======
-**grep** is a command line text search utility originally written for Unix. The name is taken from the first letters in global / regular expression / print, a series of instructions for the ed text editor. The grep command searches files or standard input globally for lines matching a given regular expression, and prints them to the program's standard output.
+**grep** is a command line text search utility originally written for Unix. The name is taken from a command for the ancient UNIX text editor **ed** - ''g/re/p'' //(global regular expression search and print)// which has the same effect. The ''grep'' command searches files or standard input globally for lines matching a given regular expression, and prints them to the program's standard output. It is one of the most essential commands you will need to use in [[tools:bash|Linux command line]].
+If you are using a modern version of Linux, chances are that ''grep'' is already installed on your system. If not, it is probably in your distro's official repositories. Consult your [[tools:package-manager|Package Manager]] for more information.
+===== Useful Commands =====
+Using ''grep'' may seem obtuse to new users at first. However, once you know how to structure your commands, it is the absolute fastest way to do many common searches:
+==== Built-in Documentation ====
+''grep --help'' and ''man grep'' will tell you all the flags which are available to use. We will only detail some of the most important ones below:
+==== Search For Lines in Files ====
+To search within //filename.txt// for the string //INSERTSTRING//, and to have grep tell you the line number it is on, use the ''-n'' flag like so:
+  $ grep -n "INSERTSTRING" filename.txt
+==== Search Files in Current Directory ====
+You can also use ''grep'' to search inside all the files within a folder, and not just one. Just replace the filename with an asterisk. To search the pwd for all files containing //INSERTSTRING//, format your command as so:
+  $ grep “INSERTSTRING” *
+You can also use the //asterisk// as a wildcard. So for all files containing //INSERT*// it would be:
+  $ grep “INSERT*” *
+Or to search for all //.txt// files containing //INSERT*// it would be:
+  $ grep “INSERT*” *.txt
+The ''-R'' flag lets you search child directories. So to search your pwd **and** all child directories recursively for all files containing //INSERTSTRING//:
+  $ grep -R "INSERTSTRING" *
+You can combine flags as well. To search your pwd and all child directories recursively for all //.txt// files containing //INSERTSTRING//, and to make grep tell you the line number that the string is found on, combine the ''-R'' and ''-n'' flags like this:
+  $ grep -Rn "INSERTSTRING" *.txt
+==== Search Files in Specific Directories ====
+To search a specific directory path for all files containing //INSERTSTRING//:
+  $ grep "INSERTSTRING" /path/to/directory/*
+The aforementioned flags work on specific directories as well:
+  $ grep -Rn "INSERTSTRING" /path/to/directory/*
-===== Download =====
+==== More Command Flags ====
-[[http://ftp.gnu.mirrors.hoobly.com/gnu/grep/|Download from GNU]]
+There are more flags you can combine with these basic ''grep'' commands to fine-tune your search. Play around with them to see how they affect output!
+  * ''-i'' - Searches made with ''grep'' are case-sensitive. Use this flag to search for both uppercase and lowercase versions of the same string.
+  * ''-l'' - Print only the filename(s) of search results. Incredibly useful when using ''-R'' on large directory trees.
+  * ''-w'' - Match only whole words.
+  * ''-x'' - Match only whole lines.
+  * ''-v'' - Inverted search. Returns only non-matching lines.
+  * ''-s'' - Suppress error messages. Useful in bash scripts.
 ===== Variations =====
-There are countless implementations and derivatives of grep available for many operating systems, as well as for aiding searches in third-party applications such as EnCase (computer forensic software). Early variants of grep included **egrep** and **fgrep**. The former applies an extended regular expression syntax that was added to Unix after Ken Thompson's original regular expression implementation. The latter searches for any of a list of 'fixed' strings using the Aho-Corasick algorithm. These variants are embodied in most modern grep implementations as command-line switches (e.g. -E and -F respectively in GNU grep). In such combined implementations, grep may also behave differently depending on the name by which it is invoked, allowing **fgrep**, **egrep**, and **grep** to be links to the same program.
+There are countless implementations and derivatives of ''grep'' available for many operating systems, as well as for aiding searches in third-party applications such as **EnCase** //(computer forensic software)//. Early variants of grep included ''egrep'' and ''fgrep''. The former applies an extended regular expression syntax that was added to Unix after Ken Thompson's original regular expression implementation. The latter searches for any of a list of 'fixed' strings using the Aho-Corasick algorithm. These variants are embodied in most modern grep implementations as command-line switches //(e.g. ''-E'' and ''-F'' respectively in GNU grep)//. In such combined implementations, grep may also behave differently depending on the name by which it is invoked, allowing ''fgrep'', ''egrep'' and ''grep'' to be links to the same program.
 **pcregrep** is an implementation of grep that uses Perl regular expression syntax.
-Other commands contain the word 'grep' to indicate that they search (usually for regular expression matches). The pgrep utility, for instance, displays the processes whose names match a given regular expression.
+Other commands contain the word ''grep'' to indicate that they search //(usually for regular expression matches)//. The **pgrep** utility, for instance, displays the processes whose names match a given regular expression.
-In [[tools:perl|Perl]], grep is a built-in function that finds elements in a list. In functional programming languages, this higher-order function is typically named "filter" instead.
+In [[tools:perl|Perl]], ''grep'' is a built-in function that finds elements in a list. In functional programming languages, this higher-order function is typically named "filter" instead.
-The DOS, OS/2 and Windows platforms provide the find command for simple string searches. Windows also provides the "findstr" command which approximates much of the functionality of “grep”, or you can use the cygwin grep ported version. A GnuWin32 version of grep is also available.
+The DOS, OS/2 and Windows platforms provide the ''find'' command for simple string searches. Windows also provides the ''findstr'' command which approximates much of the functionality of ''grep'', or you can use the the ported version in [[tools:cygwin|Cygwin]].
 ===== External Links =====
-[[http://www.gnu.org/software/grep/|GNUE official page]]
+[[https://www.gnu.org/software/grep/|Official page for grep at the GNU Project]]
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