Linux: Regular expressions and: grep tools

1. What is a regular expression:

   The regular expression is the method that handles the string, he is the behavior unit to carry on the string processing behavior, the regular expression through some special symbol's auxiliary, may let the user easily achieves the search, the deletion, replaces a certain string's handler, actually like quite with adds the position qualifier, the quantity qualifier, Character to set the range reduction match.

2.grep Tools:

First, grep is a lookup tool, and then a regular expression completes the search for the string.

There are 3 qualifiers:

The first is the character qualifier:

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Quantity qualifier:

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Position qualifier:

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Other qualifiers:

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is the extended specification for grep regular expressions, and the basic specification also has these syntaxes, just characters? +{}| () shall

interpreted as ordinary characters, to indicate that the above special meaning needs to be added \ escaped. If you use grep instead of egrep and do not add-E

parameter, the regular expression should be written in accordance with the basic specification. (Be sure to pay attention to!!!!! ）

Let's take a look at the various options for grep, and combine the various qualifiers above to use the following:

The common grep options are:
-C outputs only the count of matching rows.
- I is case-insensitive (only for single-character).
-H does not display a file name when querying multiple files.
-L Only output file names that contain matching characters when querying multiple files.
-n Displays matching lines and line numbers.
-S does not display error messages that do not exist or have no matching text.
-V Displays all lines that do not contain matching text.

One by one:

First we enter the command under Terminal: Count=0;while [$count-le];d o echo "Hello abc $count" >>file;let count++;d One

Create a 100-line file:

-C: outputs only the count of matching rows.

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-I: Case insensitive (only for single-character).

Before using this, we used the SED tool to convert the file files: the SED tool will write blog posts later.

Sed-i/he/s/he/he/g File

That means we're converting every line of he into he.

Then we use grep-i;

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-H does not display a file name when querying multiple files.

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-N Displays matching lines and line numbers.

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-S does not display error messages that do not exist or have no matching text.

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-V Displays all lines that do not contain matching text.

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-L Only output file names that contain matching characters when querying multiple files.

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This is what is commonly used =. =

This article is from the "egg-left" blog, please be sure to keep this source http://memory73.blog.51cto.com/10530560/1792687

Linux: Regular expressions and: grep tools