The grep command of the Shell scripting tool

Tag: The grep command of the Shell scripting tool

grep (abbreviated from globally search a Regular expression and Print) is a powerful text-search tool for Linux systems that can search for text using regular expressions , and print out the matching lines. Egrep and Fgrep are grep extensions that support more re- metacharacters ,fgrep is fixed grep or fast Grep.linux uses the GNU version of Grep, which is more powerful and can be used with the-G,-e,-f command-line options to use the egrep and fgrep features. grep can be used for shell script , because grep describes the status of the search by returning a status value, or 0 if the template search succeeds, or 1 if the search is unsuccessful, or 2 if the searched file does not exist. We can do some automated text processing with these return values.

Normal expression meta-characters of grep

^ Beginning Locator

$ line Footer Locator

. Match any one character

* Match 0 or more leading characters

[] matches one of the characters in the specified range

[^] matches characters not in range

\< Word Head Locator

/〉 Ending Locator

X\{m\} repeats x characters m times

X\{m,\} repeats x characters at least m times

X\{m,n\} repeats x characters m to n times

File contents:

[email protected] opt]# ll passwd
-rw-r--r--. 1 root root 1087 Mar 17:39 passwd
[email protected] opt]# cat passwd
Root:x:0:0:root:/root:/bin/bash
Bin:x:1:1:bin:/bin:/sbin/nologin
Daemon:x:2:2:daemon:/sbin:/sbin/nologin
Adm:x:3:4:adm:/var/adm:/sbin/nologin
Lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
Sync:x:5:0:sync:/sbin:/bin/sync
Shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
Halt:x:7:0:halt:/sbin:/sbin/halt
Mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
Uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin
Operator:x:11:0:operator:/root:/sbin/nologin
Games:x:12:100:games:/usr/games:/sbin/nologin
Gopher:x:13:30:gopher:/var/gopher:/sbin/nologin
Ftp:x:14:50:ftp User:/var/ftp:/sbin/nologin
[Email protected] opt]#

1.GREP command format

grep [option] character mode [filename 1, filename 2 ...]

2. Find rows starting with R

[[email protected] opt]# grep ' ^r ' passwd
Root:x:0:0:root:/root:/bin/bash
[Email protected] opt]#

3. Find the line ending in C

[[email protected] opt]# grep ' C $ ' passwd
Sync:x:5:0:sync:/sbin:/bin/sync
[Email protected] opt]#

4. Look for lines that begin with H, end with a T, and have only two characters in the middle

[[email protected] opt]# grep ' \Halt:x:7:0:halt:/sbin:/sbin/halt
[Email protected] opt]#

5. Find the contents of the file as long as there are h or Q characters

[[email protected] opt]# grep ' [HQ] ' passwd
Root:x:0:0:root:/root:/bin/bash
Shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
Halt:x:7:0:halt:/sbin:/sbin/halt
Gopher:x:13:30:gopher:/var/gopher:/sbin/nologin
[Email protected] opt]#

6. Find each line with a to O character appearing 7 times

[[email protected] opt]# grep ' [a-o]\{7\} ' passwd
Bin:x:1:1:bin:/bin:/sbin/nologin
Daemon:x:2:2:daemon:/sbin:/sbin/nologin
Adm:x:3:4:adm:/var/adm:/sbin/nologin
Lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
Mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
Uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin
Operator:x:11:0:operator:/root:/sbin/nologin
Games:x:12:100:games:/usr/games:/sbin/nologin
Gopher:x:13:30:gopher:/var/gopher:/sbin/nologin
Ftp:x:14:50:ftp User:/var/ftp:/sbin/nologin
[Email protected] opt]#

7. Find the same content in some files

[[email protected] opt]# grep root passwd*
Passwd:root:x:0:0:root:/root:/bin/bash
Passwd:operator:x:11:0:operator:/root:/sbin/nologin
Passwd1:root:x:0:0:root:/root:/bin/bash
Passwd1:operator:x:11:0:operator:/root:/sbin/nologin
[Email protected] opt]#

8. Display the line number of the grep result

[Email protected] opt]# grep root-n passwd
1:root:x:0:0:root:/root:/bin/bash
11:operator:x:11:0:operator:/root:/sbin/nologin
[Email protected] opt]#

9. Display file names that contain characters

[Email protected] opt]# grep root-l passwd
passwd
[Email protected] opt]#

10. Displaying characters in a file

[Email protected] opt]# grep root-c passwd
2
[Email protected] opt]#

11. Find content is a word

[Email protected] opt]# Grep-w halt passwd
Halt:x:7:0:halt:/sbin:/sbin/halt
[Email protected] opt]#

12. Reverse Filtering

[Email protected] opt]# grep-v Bash passwd | Grep-v Nologin passwd
Root:x:0:0:root:/root:/bin/bash
Sync:x:5:0:sync:/sbin:/bin/sync
Shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
Halt:x:7:0:halt:/sbin:/sbin/halt
[Email protected] opt]#

13. Use-E to interpret wildcard characters

[Email protected] opt]# grep-v-E ' bash|nologin ' passwd
Sync:x:5:0:sync:/sbin:/bin/sync
Shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
Halt:x:7:0:halt:/sbin:/sbin/halt
[Email protected] opt]#

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The grep command of the Shell scripting tool