grep is short for "global search regular expression and print out the line", which means to search regular expressions comprehensively and print them out. This command can be used in combination with regular expressions. It is also the most widely used command in linux.
The options of grep command are used to supplement the search process, and its command mode is very flexible, which can be variables, strings and regular expressions. Note: when a pattern contains spaces, be sure to enclose them in double quotation marks.
linux system supports three forms of grep commands. The eldest son is the representative of grep, standard and imitation. The second son is interested in love - egrep, which is referred to as the extended grep command for short. In fact, it is equivalent to grep -E and supports basic and extended regular expressions. The youngest son runs the fastest - fgrep, referred to as the fast grep command for short. In fact, it is equivalent to grep -F and does not support regular expressions. It matches according to the surface meaning of the string.
Syntax format: grep [parameter]
Common parameters:
-i | Ignore case when searching |
|---|---|
-c | Output only the number of matching rows |
-l | Only matching file names are listed, and no specific matching lines are listed |
-n | List all matching lines and display the line number |
-h | Do not display file names when querying multiple files |
-s | Do not display error messages that do not exist and do not have matching text |
-v | Displays all lines that do not contain matching text |
-w | Match whole word |
-x | Match entire row |
-r | Recursively searching |
-q | It is forbidden to output any results. The exited status indicates whether the search is successful |
-b | Prints the offset, in bytes, of the matching line from the file header |
-o | Used in combination with - b to print the offset of the header of the matched word data file, in bytes |
Reference example
Support multi file query and wildcard:
[root@linux ~]# grep zwx file_* /etc/hosts file_1:zwx file_1:zwx file_1:zwxddkjflkdjfdlkfjlsdkj file_2:zwx file_4:dkfjlzwxejfkje file_4:zwx djfkdjf file_4:zwxedkfgj
Number of output matching string lines:
[root@linux ~]$ grep -c zwx file_* file_1:2 file_2:1 file_3:0
List all matching lines and display the line number:
[root@linux ~]# grep -n zwx file_* file_1:1:zwx file_1:4:zwx file_1:10:zwxddkjflkdjfdlkfjlsdkj file_2:2:zwx file_4:3:dkfjlzwxejfkje file_4:4:zwx djfkdjf file_4:5:zwxedkfgj
Show all rows without schema:
[root@linux ~]# grep -vc zwx file_* file_1:7 file_2:4 file_3:5 file_4:2
Do not show file names again:
[root@linux ~]# grep -h zwx file_* zwx zwx zwxddkjflkdjfdlkfjlsdkj zwx dkfjlzwxejfkje zwx djfkdjf zwxedkfgj
Only the matching file names are listed, and the specific matching lines are not listed:
[root@linux ~]# grep -l zwx file_* file_1 file_2 file_4
Do not display text information that does not exist or does not match:
[root@linux ~]# grep -s zwx file1 file_1 file_1:zwx file_1:zwx file_1:zwxddkjflkdjfdlkfjlsdkj [root@linuxcool ~]# grep zwx file1 file_1 grep: file1: No such file or directory file_1:zwx file_1:zwx file_1:zwxddkjflkdjfdlkfjlsdkj
Recursive search, which searches not only the current directory but also subdirectories:
[root@linux ~]# grep -r zwx file_2 * file_2:zwx anaconda-ks.cfg:user --name=zwx --gecos="zwx" file_1:zwx file_1:zwx file_1:zwxddkjflkdjfdlkfjlsdkj file_2:zwx file_4:dkfjlzwxejfkje file_4:zwx djfkdjf file_4:zwxedkfgj initial-setup-ks.cfg:user --name=zwx --gecos="zwx"
Matching the whole word and explaining it literally is equivalent to exact matching:
[root@linux ~]# grep zw* file_1 zwx zwx zdkfjeld zw ze zwxddkjflkdjfdlkfjlsdkj [root@linuxcool ~]# grep -w zw* file_1 zw
Match the whole line. Only when the whole line in the file matches the pattern can it be printed:
[root@linux ~]# grep -x zwx file_* file_1:zwx file_1:zwx file_2:zwx
No results are output. The exited status indicates the results:
[root@linux ~]# grep -q zwx file_1 [root@linux ~]# echo $? 0 [root@linux ~]# grep -q zwx file_5 [root@linux ~]# echo $? 1 [root@linux ~]# grep -q zwx file5 grep: file5: No such file or directory [root@linux ~]# echo $? 2
Find empty and non empty lines in a file:
[root@linux ~]# grep -c ^$ file_1 4 [root@linux ~]# grep -c ^[^$] file_1 15
Match any or repeated characters with "." or "*" symbols:
[root@linux ~]# grep ^z.x file_1
zwx
zwx
zwxddkjflkdjfdlkfjlsdkj
[root@linux ~]# grep ^z* file_6
zwx
dfkjd
zzdfjkd
zz dfdww
haha