Linux grep Command Usage Introduction __linux

1. grepBrief introduction

　　 grep(The global Search Regular expression (RE) and print out of the line, which searches for regular expressions and prints the rows) is a powerful text search tool that uses regular expressions to search for text and print out matching rows. of Unix grepFamily includes grep, Egrep and Fgrep. Egrep and Fgrep's orders are only with grepThere is a very small difference. Egrep is grepExtensions that support more re meta characters, Fgrep is the fixed grepor fast grep, they treat all letters as words, that is, the metacharacters in regular expressions return to their literal meaning and are no longer special. Linux uses the GNU version of the grep。 It is more powerful and can use the EGREP and FGREP functions through the-G,-E,-F command-line Options.

　　 grepThe way it works is to search for a string template in one or more files. If the template includes spaces, it must be referenced, and all strings after the template are treated as file names. The results of the search are sent to the screen without affecting the contents of the original file.

　　 grepcan be used with shell scripts because grepIndicates the state of the search by returning a status value, returns 0 if the template search succeeds, or 1 if the search is unsuccessful, and returns 2 if the searched file does not exist. We can use these return values to do some automated text processing work.

2. grepRegular expression meta-character set (base set)

^

Anchor Line start as: ' ^grep ' matches all to grepThe beginning of the line.

$

Anchor line end like: ' grep$ ' matches all to grepThe line at the end.

Match a newline character Furu: ' GR.P ' matches the GR followed by an arbitrary character followed by P.

*

Match 0 or more previous characters Furu: ' *grep ' matches all one or more spaces followed by grepLine.. * Use to represent any character together.

[]

Matches a specified range of characters, such as ' [Gg]rep ' match GrepAnd grep。

[^]

Matches a character that is not in the specified range, such as: ' [^a-fh-z]rep ' match does not contain a letter beginning with A-r and T-z, followed by the rep line.

/(.. /)

Tags match characters, such as '/(love/) ', and Love is marked as 1.

/<

Anchor the beginning of a word, such as: '//>

Anchoring the end of a word, such as ' grep/> ' match, contains a grepThe line of the ending word.

x/{m/}

Repeat characters x,m times, such as: ' 0/{5/} ' matches rows containing 5 O.

x/{m,/}

Repeat character X, at least m times, such as: ' o/{5,/} ' matches rows with at least 5 O.

x/{m,n/}

Repeat character X, at least m times, no more than n times, such as: ' o/{5,10/} ' matches 5--10 O's line.

/w

Matches literal and numeric characters, that is, [a-za-z0-9], such as: ' G/w*p ' matches with G followed by 0 or more text or number characters, followed by P.

/w

/w, which matches one or more non word characters, such as the dot number period.

/b

Word locks, such as: '/bgrepb/' matches only grep。

3. For Egrep and grep-e meta character extension set

+

Matches one or more of the previous characters. such as: ' [a-z]+able ', match one or more lowercase letters followed by the able string, such as loveable,enable,disable.

?

Matches 0 or more previous characters. For example: ' Gr?p ' matches a gr followed by one or no characters, then a line of P.

A|b|c

Match A or B or C. such as: grep|sed matching grepor SED

()

Group symbols, such as: Love (able|rs) ov+ match loveable or lovers, matching one or more ov.

X{m},x{m,},x{m,n}

function with x/{m/},x/{m,/},x/{m,n/}

4. POSIX character class

POSIX (The Portable operating System Interface) adds special character classes, such as [: Alnum:], to keep one to the character encodings in different countries. To put them inside the [] number, you can become regular expressions, such as [a-za-z0-9] or [[: Alnum:]]. Under Linux. grepThe POSIX character classes are supported in addition to FGREP.

[: Alnum:]

Literal numeric character

[: Alpha:]

Literal characters

[:d Igit:]

numeric characters

[: Graph:]

Non-null characters (not spaces, control characters)

[: Lower:]

lowercase characters

[: Cntrl:]

Control characters

[:p rint:]

Non-null characters (including spaces)

[:p UNCT:]

Punctuation

[: Space:]

All white-space characters (new lines, spaces, tabs)

[: Upper:]

Uppercase characters

[: Xdigit:]

hexadecimal digits (0-9,a-f,a-f)

5. GrepCommand options

-?

Displays both the top and bottom of the matching row. Rows, such as: grep-2 pattern filename Displays the top and bottom 2 rows of the matching row at the same time.

-b,--byte-offset

Print the block number in which the line is printed before the matching line.

-C,--Count

Prints only the number of rows that match and does not display the matching content.

-F File,--file=file

Extracts the template from the file. The empty file contains 0 templates, so nothing matches.

-h,--no-filename

When searching for multiple files, the matching filename prefix is not displayed.

-i,--ignore-case

ignores case differences.

-q,--quiet

Suppresses display and returns only the exit status. 0 indicates that a matching row was found.

-l,--files-with-matches

Print a list of files that match the template.

-l,--files-without-match

Print a list of files that do not match the template.

-n,--line-number

Print the line number before the matching line.

-s,--silent

Does not display error messages about the absence or inability to read files.

-v,--revert-match

Reverse retrieve, showing only rows that do not match.

-w,--word-regexp

If referenced by/< and/>, the expression is searched as a word.

-v,--version

Displays software version information.

6. Examples

To use good grepThis tool, in fact, is to write a regular expression, so this is not the case grepOf all the functions of the example, only a few examples, to explain a regular expression of the wording.

$ ls-l | grep' ^a '

Filters the contents of the LS-L output through a pipe, showing only the rows that start with a.

$ grep' Test ' d*

Displays the rows that contain test in all files that start with D.

$ grep' Test ' AA bb cc

Displays the row that matches test in the aa,bb,cc file.

$ grep' [a-z]/{5/} ' AA

Displays all the lines that contain at least 5 consecutive lowercase characters for each string.

$ grep' W/(es/) T.*/1 ' AA

If West is matched, the es are stored in memory and labeled 1, then search for any character (. *), followed by another ES (/1), and the line is displayed. If you use Egrep or grep-E, you do not use the "/" to escape, directly written ' W (es) T.*/1 ' on it.