RetroSearch Browse

Home - News ( United States | United Kingdom | Italy | Germany ) - Football scores

Showing content from https://www.geeksforgeeks.org/linux-unix/regular-expression-grep/ below:

Regular Expression in grep - GeeksforGeeks

Regular Expression in grep

Last Updated : 30 Jan, 2019

Prerequisite:

grep

Basic Regular Expression

Regular Expression provides an ability to match a "string of text" in a very flexible and concise manner. A "string of text" can be further defined as a single character, word, sentence or particular pattern of characters. Like the shell’s wild–cards which match similar filenames with a single expression, grep uses an expression of a different sort to match a group of similar patterns.

[ ]: Matches any one of a set characters
[ ] with hyphen: Matches any one of a range characters
^: The pattern following it must occur at the beginning of each line
^ with [ ] : The pattern must not contain any character in the set specified
$: The pattern preceding it must occur at the end of each line
. (dot): Matches any one character
\ (backslash): Ignores the special meaning of the character following it
*: zero or more occurrences of the previous character
(dot).*: Nothing or any numbers of characters.

Examples

(a) [ ]

: Matches any one of a set characters

$grep  “New[abc]”  filename

It specifies the search pattern as :

Newa , Newb or Newc

$grep  “[aA]g[ar][ar]wal”  filename

It specifies the search pattern as

Agarwal , Agaawal , Agrawal , Agrrwal

agarwal , agaawal , agrawal , agrrwal

(b) Use [ ] with hyphen

: Matches any one of a range characters

$grep  “New[a-e]” filename

It specifies the search pattern as

Newa , Newb or Newc , Newd, Newe

```
$grep  “New[0-9][a-z]”  filename
```
It specifies the search pattern as: New followed by a number and then an alphabet.
```
New0d, New4f etc
```

(c ) Use ^

: The pattern following it must occur at the beginning of each line

$grep  “^san”  filename

Search lines beginning with san. It specifies the search pattern as

sanjeev ,sanjay, sanrit , sanchit , sandeep etc.

```
$ls –l |grep  “^d” 
```
Display list of directories only
```
$ls –l |grep  “^-” 
```
Display list of regular files only

(d) Use ^ with [ ]

: The pattern must not contain any character in the set specified

```
$grep  “New[^a-c]”  filename
```
It specifies the pattern containing the word “New” followed by any character other than an ‘a’,’b’, or ‘c’
```
$grep  “^[^a-z A-Z]”  filename
```
Search lines beginning with an non-alphabetic character

(e) Use $

: The pattern preceding it must occur at the end of each line

$ grep "vedik$" file.txt

(f) Use . (dot)

: Matches any one character

$ grep "..vik" file.txt
$ grep "7..9$" file.txt

(g) Use \ (backslash)

: Ignores the special meaning of the character following it

```
$ grep "New\.\[abc\]" file.txt
```
It specifies the search pattern as New.[abc]

$ grep "S\.K\.Kumar" file.txt

It specifies the search pattern as

S.K.Kumar

(h) Use *

: zero or more occurrences of the previous character

$ grep "[aA]gg*[ar][ar]wal" file.txt

(i) Use (dot).*

: Nothing or any numbers of characters.

$ grep "S.*Kumar" file.txt

RetroSearch is an open source project built by @garambo | Open a GitHub Issue

Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo

HTML: 3.2 | Encoding: UTF-8 | Version: 0.7.4