Pattern searching using grep

The g/RE/p stands for globally search for the regular expression (RE) and print out the line.

Return status – success 0, pattern not found 1, file not found 2.

$  ps -ef | grep root

The preceding command will show all processes running currently whose user ID is "root".

$  ll /proc | grep "cpuinfo"

The preceding command will show the file with the name cpuinfo from the /proc directory.

$  grep –lir "text" *   // only file names  //   
$ grep –ir  "text" dir_name   // show lines of files //

We will try the following commands on the love.txt file:

Metacharacter	Function	Example	Description
`^`	Beginning-of-line anchor	`'^mango'`	Will display all lines beginning with `mango`
`$`	End-of-line anchor	`'mango'$'`	Will display all lines ending with `mango`
`.`	Matches single character	`'m..o'`	Will display lines containing `m`, followed by two characters, followed by an `o`
`*`	Matches zero or more characters preceding the asterisk	`'*mango'`	Will display lines with zero or more spaces, followed by the pattern `mango`
`[ ]`	Matches single character in the set	`'[Mm]ango'`	Will display lines containing `Mango` or `mango`
`[^]`	Matches single character not in the set	`'[^A–M]ango'`	Will display lines not containing a character in the range `A` through `M`, followed by `ango`
`\<`	Beginning-of-word anchor	`'\<mango'`	Will display lines containing a word that begins with `mango`
`\>`	End-of-word anchor	`'mango\>'`	Will display lines containing a word that ends with `mango`

We will create a new file sample.txt, as follows:

Apple  Fruit    5  4.5
Potato  Vegetable  4  .5
Onion  Vegetable  .3  8
Guava  Fruit    5  1.5
Almonds  Nuts    1  16
Tomato  Vegetable  3  6
Cashew  Nuts    2  12
Mango    Fruit    6  6
Watermelon  Fruit    5  1

We will try the following commands on the sample.txt file:

Sr. no.	Command	Description
1	`grep Fruit sample.txt`	This will show all lines with pattern `Fruit`.
2	`grep Fruit G*`	This searches pattern `Fruit` in all files starting with `G`.
3	`grep '^M' sample.txt`	This searches all lines starting with `M`.
4	`grep '6$' sample.txt`	This searches lines ending with `6`.
5	`grep '1\..' sample.txt`	This displays lines containing 1 and any character after it.
6	`grep '\.6' sample.txt`	This shows lines containing .`6`.
7	`grep '^[AT]' sample.txt`	This searches lines starting with `A` or `T`.
8	`grep '[^0-9]' sample.txt`	This contains at least one alphabet.
9	`grep '[A-Z][A-Z] [A-Z]' sample.txt`	This searches the upper case, upper case space, and upper case word.
10	`grep '[a-z]\{8\}' sample.txt`	This displays all lines in which there are at least eight consecutive lowercase letters.
11	`grep '\<Fruit' sample.txt`	This displays all lines containing a word starting with Fruit. The `\<` is the beginning-of-word anchor.
12	`grep '\<Fruit\>' sample.txt`	This displays the line if it contains the word `Fruit`. The `\<` is the beginning-of-word anchor and the `\>` is the end-of-word anchor.
13	`grep '\<[A-Z].*o\>' sample.txt`	This displays all lines containing a word starting with an uppercase letter, followed by any number of characters and a word ending in `o`.
14	`grep -n '^south' sample.txt`	This displays line numbers also.
15	`grep –i 'pat' sample.txt`	This displays case insensitive search.
16	`grep -v 'Onion' sample.txt > temp` `mv temp sample.txt`	This deletes the line containing pattern.
17	`grep –l 'Nuts' *`	This lists files containing pattern.
18	`grep –c 'Nuts' sample.txt`	This prints the number of lines where pattern is present.
19	`grep –w 'Nuts' sample.txt`	This counts where the whole world pattern is present, not a part of the word.

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Table of Contents for Learning Linux Shell Scripting

Pattern searching using grep

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Learning Linux Shell Scripting