An example Analysis of regular expression in Linux

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Regular expression (regular expression) describes a string matching pattern (pattern), which can be used to check whether a string contains a certain substring, replace a matching substring, or extract a substring from a string that meets a certain condition.

Metacharacters are usually divided into two categories in Linux: Shell metacharacters, which are parsed by Linux Shell; regular expression metacharacters, which are parsed by text processing tools such as vi/grep/sed/awk; and regular expressions are generally processed as text lines. Set the-color parameter for the grep command before performing the following example:

Class= "" > $alias grep='grep-- color=auto'

In this way, the string filtered out each time will be colored.

One more thing to do before you begin is to create a re-file file for testing, as follows:

Class= "" > $cat re-fileI had a lovely time on our little picnic.Lovers were all around us. It is springtime. Ohlove, how much I adore you. Do you knowthe extent of my love? Oh, by the way, I thinkI lost my gloves somewhere out in that field ofclover. Did you see them? I can only hope love.is forever. I live for you. It's hard to get back in thegroove.class= "> $cat linux.txtLinux is a goodgod assdxw bcvnbvbjkgreatttttt wexcvxcoperaaaating dhfghfvxgooodfs awrerdxxhklgdsystem awxxxxgladgood regular expression metacharacter special metacharacter extension regular expression

Teach you 3 minutes to finish Linux regular expression teach you 3 minutes to finish Linux regular expression practice

Match all lines that start with love

Class= "> $grep'^ love' re-filelove, how much I adore you. Do you know

Match all lines at the end of love

Class= "> $grep 'love$' re-fileclover. Did you see them? I can only hope love.

Matches all lines that start with l, contain two characters in the middle, and end with e

Class= "" > $grep'l... e' re-fileI had a lovely time on our little picnic.love, how much I adore you. Do you knowthe extent of my love? Oh, by the way, I thinkI lost my gloves somewhere out in that field ofclover. Did you see them? I can only hope love.is forever. I live for you. It's hard to get back in the

Matches 0 or more blank lines, followed by love characters

Class= "" > $grep'* love' re-fileI had a lovely time on our little picnic.love, how much I adore you. Do you knowthe extent of my love? Oh, by the way, I thinkI lost my gloves somewhere out in that field ofclover. Did you see them? I can only hope love.

Match love or Love

Class= "> $grep'[Ll] ove' re-file # is case-insensitive to l. It is springtime. Ohlove, how much I adore you. Do you knowthe extent of my love? Oh, by the way, I thinkI lost my gloves somewhere out in that field ofclover. Did you see them? I can only hope love.

Matches the letter Amurz, followed by ove

Class= "" > $grep'[Amurz] ove' re-fileLovers were all around us. It is springtime. Oh

Match any character lines that are not in the Amurz range, all lowercase characters

Class= "" > $grep'[^ Amurz] 're-fileI had a lovely time on our little picnic.Lovers were all around us. It is springtime. Ohlove, how much I adore you. Do you knowthe extent of my love? Oh, by the way, I thinkI lost my gloves somewhere out in that field ofclover. Did you see them? I can only hope love.is forever. I live for you. It's hard to get back in thegroove.

Match love

Class= "" > $grep 'love\. " Re-fileclover. Did you see them? I can only hope love.

Match Spac

Class= "> $grep'^ $'re-file

Match any character

Class= "> $grep'. * 're-fileI had a lovely time on our little picnic.Lovers were all around us. It is springtime. Ohlove, how much I adore you. Do you knowthe extent of my love? Oh, by the way, I thinkI lost my gloves somewhere out in that field ofclover. Did you see them? I can only hope love.is forever. I live for you. It's hard to get back in thegroove.

The preceding o character is repeated 2 to 4 times

Class= "> $grep'o\ {2pm 4\} 're-filegroove.

Repeat the o character at least 2 times

Class= "> $grep'o\ {2,\} 're-filegroove.

Repeat 0 character up to 2 times

Class= "> $grep'o\ {, 2\} 're-fileI had a lovely time on our little picnic.Lovers were all around us. It is springtime. Ohlove, how much I adore you. Do you knowthe extent of my love? Oh, by the way, I thinkI lost my gloves somewhere out in that field ofclover. Did you see them? I can only hope love.is forever. I live for you. It's hard to get back in thegroove.

Repeat one or more of the previous character

Class= "> $egrep" go+d "linux.txtLinux is a goodgod assdxw bcvnbvbjkgooodfs awrerdxxhklgood#0 or one character ansheng@Ubuntu:/tmp$ egrep" go?d "linux.txtgod assdxw bcvnbvbjkgdsystem awxxxx

Or, find multiple strings

Class= "" > $egrep "gd | good" linux.txtLinux is a goodgdsystem awxxxxgood

Packet filter matching

Class= "> $egrep" g (la | oo) d "linux.txtLinux is a goodgladgood is all the content of the article" regular expression example Analysis of Linux ". Thank you for reading! I believe you will gain a lot after reading this article. The editor will update different knowledge for you every day. If you want to learn more knowledge, please pay attention to the industry information channel.