Linux Shell Learning

-- ECHO command

var='hello world!'

echo 'var=' $var

 

 

 

 

-- LOGICAL

 

---- &&    command :

---- ---- command1 && command2

---- ---- ---- if command1 is true, then execute command2; if command1 is false, then not execute command2.

---- ||    command :

---- ---- command1 || command2

---- ---- ---- if command1 is true, then not execute command2; if command1 is false, then execute command2. 

 

---- &&   condition:

---- ---- [[  bool-expression1  &&  bool-expression2  ]]

---- ||     condition:

---- ---- [[  bool-expression1  ||  bool-expression2  ]]

 

----    -a  condition:

---- ---- [  bool-expression1  -a  bool-expression2  ]

----    -o  condition:

---- ---- [ bool-expression1  -o  bool-expression2  ]