Detailed explanation of grep command parameters

1. grep command parameter options

-? Simultaneously display the upper and lower lines of matching lines, such as grep -2 'pattern' filename,
-A ? Simultaneously display the lower lines of matching lines grep -A 10 'pattern' filename
-B ? At the same time, display the matching lines? Line
-c prints the number of matches
-E Extended regular egrep

-f Two files have the same line. For example, grep -f file1 file2
-F fgrep
-h does not display the file name of the matching line
-H Displays both line and file names
-i Ignores case
-l Only displays matching file names
-n Displays line numbers
-o Only displays matching characters
-r Recursive query
-v Only displays not Matched lines

2. grep regular expression metacharacter set (basic set)

^ The beginning of the anchor line such as: '^grep' matches all lines starting with grep.
$ End of anchor line For example: 'grep$' matches all lines ending with grep. ^$ is used together to represent a blank line
. Matches a non-newline character. For example: 'gr.p' matches gr followed by any character, then p.
* matches zero or more previous characters. For example: '*grep' matches all lines with one or more spaces followed by grep. .* used together represents any character.
[] matches characters within a specified range, such as '[Gg]rep' matches Grep and grep.
[^] matches a character that is not within the specified range, such as: '[^A-FH-Z]rep' matches a line starting with a letter that does not contain A-R and T-Z, followed by rep.
.. mark matching characters, such as 'love', love is marked as 1.
< Anchor the beginning of a word, such as: '> Anchor the end of a word, such as 'str>' matches lines containing words ending with str.
x{m}
Repeat character x, m times, for example: 'a{5}' matches a line containing 5 a's.
x{m,}
Repeat character x at least m times, for example: 'a{5,}' matches lines with at least 5 a's.
x{m,n}
Repeat the character The metacharacter extension set of E

+ matches one or more previous characters. For example: '[a-z]+able', matches a string of one or more lowercase letters followed by able, such as loveable, enable, disable, etc.

? Matches zero or more previous characters. For example: 'gr?p' matches lines with gr followed by one or no characters, then p.

a|b|c
matches a or b or c. For example: grep|sed matches grep or sed
() grouping symbols, such as g(la|oo)d matches glad or good
()+ multiple repeated grouping matches, such as A(xy)+B matches the beginning of A and the end of B More than one xy such as AxyB.AxyxyB.AxyxyxyB
x{m},x{m,},x{m,n}
has the same effect as x{m},x{m,},x{m,n}

4. POSIX character classes

[:alnum:] 0-9, A-Z, a-z

[:alpha:] A-Z, a-z

[:digit:] 0-9
[:lower:] a-z
[:upper: ] A-Z