Bash regular expression, text file find grep egrep

1. Syntax + options

syntax: grep [-CINVABC] ' word ' filename
-C: Print the number of lines that meet the requirements
- N: Output with the same number of lines as required
-V: Print rows that do not meet the requirements
-A: followed by a number (with or without spaces), e.g. –A2
prints the line that meets the requirements and the following two lines
-B: followed by a number, such as –B2, indicates that the print meets the requirements
Line and the above two lines
-C: followed by a number, such as –C2, indicates that printing meets the requirements
rows and two rows above and below each other .
-R: All files under the directory are traversed
grep-r ' root '/etc/all files in the directory are checked all the time

[0-9] take any 1 of the brackets


2. Example Introduction
filter out a line with a keyword and enter the travel number grep-n ' root ' 1.txt
filter out lines without a keyword and lose travel number grep-n-V ' root ' 1.txt
filter out all rows that contain numbers grep ' [0-9] ' 1.txt
filter out all lines that do not contain numbers grep-v ' [0-9] ' 1.txt
Remove all lines beginning with ' # ' grep-v ' ^# ' 1.txt
Remove all empty lines and lines beginning with ' # ' grep-v ' ^$ ' 1.txt|grep-v ' ^# '
filter out lines that begin with the English alphabet grep ' ^[a-za-z] ' 1.txt
filter out lines that start with a non-digit grep ' ^[^0-9] ' 1.txt
filter any one or more characters grep ' r.o ' 1.txt;
grep ' r*t ' 1.txt; grep ' r.*t ' 1.txt
. Represents any one character; * represents 0 or more preceding characters;
. * Denotes 0 or more arbitrary characters, and a blank line is included
Specify the number of filter characters grep ' o\{2\} ' 1.txt

3. Egrep
The Egrep tool is an extension of the grep tool
egrep ' o+ ' 1.txt means 1 or more than 1 preceding characters
egrep ' O? ' 1.txt represents 0 or 1 preceding characters
egrep ' roo|body ' 1.txt match roo or match body
egrep ' r (oo) | (at) o ' 1.txt brackets denote a whole
egrep ' (oo) + ' 1.txt denotes 1 or more ' oo '

4.. * + ? Summarize
. Represents any one character (including special characters)
* Represents 0 or more * preceding characters
. * denotes any arbitrary character (contains blank lines)
+ represents 1 or more + preceding characters
？ Represents 0 or 1 characters in front of each other
where, +? GREP is not supported, EGREP is supported.

^ The character following the beginning of the anchor line, which must appear at the beginning of the line

$ anchor Line end, character following this character, must appear at the end of the row

"^" in [^] denotes non-meaning

^$ Empty Line

Any character after \< or \b must appear as the hand of the word.

Any character in front of the \> or \b must appear as the tail of the word

\<root\> for the whole word

\ (\) Group: \ (ab\) * Indicates the presence of any AB

Extended groupings do not need to be added to the meaning;

A|b means A or B.

This article is from the "you and I Walk" blog, please be sure to keep this source http://ondali.blog.51cto.com/6650368/1615962

Bash regular expression, text file find grep egrep