Linux Shell Study Notes 10

14th class hour Functions

14.1 create and use functions

Format: Name () {list ;}

 

An important feature of Shell functions is that they can be used to replace binary executable files or shell built-in commands with the same name.

For example:

CD () {chdir $ {1:-$ home}; PSI = "'pwd' $"; export PSI ;}

This statement uses a function instead of the CD command, which changes the Directory and sets the main shell prompt $ PSI to include the current directory.

 

Function variables in shell scripts do not work with other scripting languages. For example, in PHP, when the script execution exceeds the function range, the internal variables

Will disappear, so there is no problem if you do not delete it.

In Shell, variables are identified as global variables, so they must be managed with caution.

 

For example:

$ Test () {test = 123 ;}

$ Test

$ Echo $ test # output 123

 

 

 

15th Lesson text filter

Shell scripts are often called to operate and format the output of the executed command.

1) Head

2) tail

3) grep

4) sort

5) uniq

6) tr

 

15.1.1 head and tail commands

Format: head [-n lines] files

If no-n lines exist, the first 10 lines of the standard are displayed.

 

15.1.2 tail command

Format: tail [-n lines] files

If no-n lines exist, the last 10 lines of the standard are displayed.

-F option, used to view the file that is being written.

 

 

15.2 use grep

The grep command allows you to find a line containing a special word or phrase in the file.

 

15.2.1 search for words

Format:

Grep Word file

Here, the file specifies the files in which the word is to be searched. The grep command displays each line of the word in the file.

When multiple files are specified, the grep command adds the file name containing the row before the output line.

-I option, case insensitive.

 

15.2.2 read from stdin (standard input)

When no file is specified, grep looks for a match from the stdin input line, which makes it well connected to the pipeline.

Example: $ who | grep Root

-V option to list rows that do not match the condition

 

15.2.3 row number

Option-n. The result list returns the row number.

$ Grep-N pipe ch15.doc

Return format: file: line number: Line

 

15.2.4 only list file names

Sometimes, you only need to return a file name containing a word.

You can use the-L option.

Example: $ grep-l PHP *

Return Value: index. php