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  Linux command execution judge sentences -;, &&, ||
     
  Add Date : 2018-11-21      
         
         
         
  Command execution judgment basis -;, &&, ||

In the Linux operation and maintenance during the ordinary course or Linux operating system will execute multiple commands at the same time, so we need multiple commands manner.

1.

By using the ';' semicolon to execute multiple commands, such as for example:

#sync; sync; shutdown -h now

2.

Run by the judge, && / || the implementation of such cases:

cmd1 && cmd2:

If cmd1 completed and executed correctly ($? = 0), then started cmd2

If cmd1 completed and incorrect execution ($?! = 0), then open cmd2 not executed

cmd1 || cmd2:

If after cmd1 completed execution ($? = 0) is correct, cmd2 not executed.

If completed after cmd1 error ($?! = 0), then started only cmd2

According to the above exercise to learn the contents of the following exercises:

1.

Analyzing / home directory exists a file is created lshome

#ll / home && touch / home / lshome

2.

Determine whether there is create a file / tmp / abc, if / tmp / abc does not exist, create

#ls -l / tmp / abc || mkdir / tmp / abc

3. Analyzing / home / Samlee directory exists, if there is displayed "exist", if there is no will display "not exist"

#ls -l / home / Samlee && echo "exist" || echo "not exist"
     
         
         
         
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