Linux Learning---Regular expressions and grep

Regular Expressions (Regular expression (RE))

is through the arrangement of some special characters to "search/replace/delete" one or more columns of text string, in short, the regular expression is used in the processing of a string "expression" above. Regular expressions are not a tool program, but a standard basis for string processing, and if you want to use regular expressions to handle strings, you will need a tool program that supports regular expressions, such as VI, awk, grep, sed ...

Grep

Basic rules:

grep ' Search String ' filename

Options and Parameters:

-A: Search data in binary archives in text file mode

-C: Calculates the number of ' search string ' found

-I: Ignore case

-N: Output line number

-V: Reverse selection, which displays rows without a ' search string ' content

Example

1. Remove the line that appears root in the last

 Last grep ' Root '

2. As opposed to 1, as long as there is no root line

 Last grep ' Root '

3. Remove the/etc/man.config containing the Manpath and display the line number

grep ' MANPATH ' -n/etc/man. config

Plus the--color=auto option, the keywords you find are displayed in a special color.

Advanced

Rules:

grep ' Search String ' filename

Options and Parameters:

-A: The following can be added to the number, in the meaning of After, in addition to listing the row, the subsequent n rows are also listed

-B: The following can be added as a number, for the meaning of befer, in addition to listing the row, the previous n rows are also listed

Example

1.

grep ' ETH '

The DMESG can list the core-generated messages and access the network card-related information via grep (ETH).

2. With the title, the first two lines of the keyword line and the last three lines are also displayed:

grep ' ETH '

3. Use the brackets [] to search for set characters

If you want to search for test or taste these two words, you can find that they have a common ' t?st ' existence, this time,
I can search for this:

grep ' t[ae]st ' filename

4. We can use,

grep ' oo ' filename

To search for a line that contains ' oo ', so maybe or search for a bunch of words good, food ... Line, what if we don't want ' oo ' in front of ' G '? You can use the inverse selection of the set character [^]:

grep ' [^g]oo ' filename

If you don't want ' oo ' to have lowercase letters, we can write this:

grep -n [^a-z]oo'  filename

That is, for consecutive females or numbers, you can write this [a-z], [A-z], [0-9].

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