grep, Egrep, and corresponding regular expression usages

The Grep,egrep command in a Linux system is a powerful text search tool that uses regular expressions and extended regular expressions to search for text and print the rows that match.

1. Search for a specific string "the" Note: N is the display line number

# grep-n ' the ' regular_express.txt

2. Use the- v option to reverse the search for a specific string "the"

# grep-vn ' the ' regular_express.txt

3. Match the string with the case "the", using the-i option

# grep-in ' the ' regular_express.txt

4.[] Indicates a string matching "[]" in the range

When I search for the two words of test or tast, I find that they have a common ' t?st ', so we can search for them.

# grep-n ' t[ae]st ' regular_express.tx

Note: uppercase English/lowercase English/numbers can be written using [a-z]/[a-z]/[0-9], or can be written together

[A-za-z0-9] indicates that a string is required to be numeric and English

If we want to get the line with numbers, then:

# grep-n ' [0-9] ' regular_express.txt

can also be used

[[: Lower:]] instead of a-Z

[[:d Igit:]] instead of 0-9

[[: Upper:]]: all uppercase letters;

[[: Lower:]]: all lowercase letters;

[[:d Igit:]]: all numbers;

[[: Alpha:]]: all letters;

[[: Space:]]: white space characters;

[[:p UNCT:]]: punctuation;

Example: # grep-n ' [^[:lower:]]oo ' Regular_express.txt

# grep-n ' [[:d igit:]] ' regular_express.txt, etc.

5.[^] Represents a string outside the range of "[]", such as [^0-9] for non-numeric characters, [^a-z] for non-uppercase character ranges

If we want to get the line without numbers, then:

# grep-n ' [0-9] ' regular_express.txt

6.^word represents a matching string (word) at the beginning of the line

Displays the string at the beginning of ' the '

# grep-n ' ^the ' regular_express.txt

Displays the beginning of the line as lowercase characters

# grep-n ' ^[a-z] ' regular_express.txt

7.word$ represents a matching string (word) at the end of a row

Displays the end of the line as a point. The line

# grep-n ' \.$ ' regular_express.txt

Show Blank Lines

# grep-n ' ^$ ' regular_express.txt

8.. sign to match 1 arbitrary characters

Find out g?? D string, beginning G four string ending D

# Grep-n ' G.. d ' Regular_express.txt

9. * Indicates a match of 0 to infinity (regular expression) before one character

"Goo*g" stands for Gog,goog,gooog ... such as

# grep-n ' Goo*g ' regular_express.txt

10. \ = Matches the preceding character 0 or 1 times

Match the O character 0 or one time

# grep-n Ro\?t Regular_express.txt

11. \+ matches the preceding character at least once

Match a string that contains at least one O character

Grep-n ro\+t Regular_express.txt

Note: the. symbol represents any character,. * represents an empty character or one to n any character

Find a string with two g in the middle containing any character

# grep-n ' G.*g ' regular_express.txt

\ denotes an escape character, preceded by a special character, will remove the meaning of the original special character

Note: {} because there is a special meaning in the shell, you need to add the signifier \ to make it meaningless.

\{m,n\} means finding the first character of N to M (regular expression)

Find a string with two O

# grep-n ' o\{2\} ' regular_express.txt

Find the string after G that contains 2 to 5 O and ends with a G

# grep-n ' Go\{2,5\}g ' regular_express.txt

\{n,\} represents more than n previous re characters

Find the string after g that contains more than 2 O and ends with G

# grep-n ' Go\{2,\}g ' regular_express.txt

\< or \b Indicates the first anchor of the word.

Find the string with the "RO" string at the beginning of the word

# grep-n "ro\<" Regular_express.txt

\> or \b indicates a final anchor

Find the string at the end of the word with the "ro" string

# grep-n "\>ro" Regular_express.txt

Egrep supports the use of extended regular expressions, which are basically the same as grep usage, except that the egrep is in addition to the final and final anchors

"<" ">" symbol to use "\" to change the meaning, the other symbols are not used,

Example:

1. + represents repeating one or more of the previous re characters

Example: Egrep ' Go+d ' regular_express.txt

Expression Search (God) (good) (Goood) ... And so on string, o+ stands for [more than one o]

2.? Represents a repeat of 0 or one of the previous re characters

Example: Egrep ' Go?d ' regular_express.txt

Represents a search (GD) string, o represents [empty or 1 O]

3. () indicates finding the group string

Example: Egrep ' G (la|oo) d ' regular_express.txt

Represents a search (glad) or (good) string

4. () + indicates identification of multiple repeating groups

Example: Echo ' axyzxyzxyzxyzxyzc ' |egrep ' A (xyz) +c '

Indicates that the search begins with a ending is C, with more than one ' xyz ' string in the middle

The rest of the usage is not a detailed example that mimics grep usage:

Range Matching:

The. Number means matching any single character

[]: matches any single character within the range

[^]: matches any single character outside the range

Number of matches:

*: Matches any time

?: matches 0 or 1 times

+: Match 1 or more times

{m}: match matches m times

{M,n}: matches at least m times, up to N times

{0,n}: matches at least 0 times up to unlimited times

{m,}: matches at least m times

Location Matching:

^ Indicates the beginning of the line anchoring

$ indicates end of line anchoring

\< or \b Indicates the first anchor of the word

\> or \b indicates a final anchor

This article is from the "Linux" blog, so be sure to keep this source http://wyg11.blog.51cto.com/11253863/1750068

grep, Egrep, and corresponding regular expression usages