[Shell] bash basic functions: Multi-command sequential execution and pipeline operators

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1. Multiple commands are executed sequentially.

Semicolon (;)

Logic and (&&)

Logic or (|)

 

Semicolon:

Ls;Date;CD/user;PWD

Execution sequence: commands are executed sequentially. There is no relation between commands and they do not affect each other.

Purpose: connect multiple commands to simplify operations

 

Example:

Dd If = input file of = output file BS = Bytes Count = count (used to copy a disk)

(Date; dd If =/dev/Zero of =/home/testfile BS = 1 k count = 10000; Date) # Count the execution time

Option:

If = input file specifies source file or Source Device

Of = specifies the target file or target device for the output device.

BS = the number of bytes specifies the number of bytes input/output at a time, that is, these bytes are considered as a data block.

Count = number of data blocks specified for Input/Output

 

Logic and:

　　Ls & Echo Yes

Execution sequence: The second command is executed only when the first command is successfully executed.

Purpose: The command has a logical relationship and must have a certain execution order.

 

Logic or:

　　Ls | echo No

Execution sequence: the first is successfully executed, the second is not executed; the first is not executed correctly, and the second is executed

Purpose: Determine whether the previous command is correctly executed

 

Use of logic and logic or combination:

　　Command & Echo Yes | echo No# Use this method to determine whether the command is executed

 

2. pipeline operator:

　　Command 1 | command 2# Use the result of command 1 as the operation object of command 2

Example:

Ls-L | more # display the correct command execution result on multiple screens

　　

　　Grep [Option] 'search content' file name# Search for matching strings in the file

Option:

-I case-insensitive

-N: Output row number

-V reverse lookup

-- Color = the keywords searched by auto are displayed in color.

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