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What are the grep commands in Linux? I believe that many inexperienced people are at a loss about this, so this article summarizes the causes and solutions of the problem. Through this article, I hope you can solve this problem.

Grep command is a powerful text search tool in Linux system. It can use regular expressions to search text and print matching lines. The full name of grep is Global Regular Expression Print, which represents the global regular expression version, and its permission is for all users.

1. Action

Grep command is a powerful text search tool in Linux system. It can use regular expressions to search text and print matching lines. The full name of grep is Global Regular Expression Print, which represents the global regular expression version, and its permission is for all users.

The grep family includes grep, egrep and fgrep. The commands of egrep and fgrep are only slightly different from grep. Egrep is an extension of grep to support more re metacharacters. Fgrep is fixed grep or fast grep, which treats all letters as words, that is, metacharacters in regular expressions express their own literal meaning and are no longer special. Linux uses the GNU version of grep. It is more powerful, and you can use the functions of egrep and fgrep through the-G,-E,-F command line options.

two。 Format and main parameters

Grep [options]

Main parameters: grep-help can be viewed

-c: outputs only the count of matching rows.

-I: case-insensitive.

-h: the file name is not displayed when querying multiple files.

-l: when querying multiple files, only the file names that contain matching characters are output.

-n: displays matching lines and line numbers.

-s: does not display error messages that do not exist or have no matching text.

-v: displays all lines that do not contain matching text.

-- color=auto: you can add the color display to the keywords you find.

The main parameters of the pattern regular expression:

\: ignore the original meaning of special characters in regular expressions.

^: matches the start line of the regular expression.

$: matches the end line of the regular expression.

\: to the end of the line matching the regular expression.

[]: single character, such as [A], that is, A meets the requirements.

[-]: range, such as [Amurz], that is, A, B, C all the way up to Z meet the requirements.

.: all single characters.

*: all characters, the length can be 0.

The 3.grep command uses a simple example

Itcast$ grep 'test' d *

Show lines that contain test in all files that begin with d

Itcast $grep 'test' aa bb cc

Displays the lines that match the test in the aa,bb,cc file.

Itcast $grep'[a murz]\ {5\}'aa

Displays all lines that contain at least five consecutive lowercase characters for each string.

Itcast $grep w\ (es\) t.*\ 1' aa

If the west is matched, the es is stored in memory and marked as 1, and then any character (. *) is searched, followed by another es (\ 1), and the line is displayed when found. If you use egrep or grep-E, instead of using the "\" sign for escape, you can just write'w (es) t. *\ 1'.

The 4.grep command uses complex instances

Explicitly request to search for subdirectories:

Grep-r

Or omit subdirectories

Grep-d skip

If you have a lot of output, you can pipe it to 'less' to read:

Itcast$ grep magic / usr/src/Linux/Documentation/* | less

In this way, you can read it more easily.

It is important to note that you must provide a file filtering method (use * to search all files). If you forget, 'grep' will wait until the program is interrupted. If you encounter such a situation, press and try again.

Here are some interesting command-line arguments:

Grep-i pattern files: search insensitive to case. The default is case sensitive

Grep-l pattern files: lists only matching file names

Grep-L pattern files: lists mismatched file names

Grep-w pattern files: matches only the whole word, not part of the string (such as matching 'magic', instead of' magical')

Grep-C number pattern files: the matching context displays [number] lines respectively.

Grep pattern1 | pattern2 files: displays lines that match pattern1 or pattern2

For example: grep "abc\ | xyz" testfile means to filter rows containing abc or xyz

Grep pattern1 files | grep pattern2: displays lines that match both pattern1 and pattern2.

Line number information can be displayed by grep-n pattern files

You can find the total number of rows by grep-c pattern files

There are also some special symbols for search:\

Mark the beginning and end of the word respectively.

For example:

Grep man * will match 'Batman',' manic', 'man', etc.

Grep'\

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