The edevil Linux-shell tips on If sentence

By failing time after time, I finally master the tricks of writing Linux Shell, the most classical examples were the usage of 'if' sentence in Shell language. Here are the tips and samples:

 

Semantics:

 

If [conditions]; then

Command

Fi

 

Such as test the existance of a file, we use:

 

If [-F "FILENAME"]; then

Echo Yes

Fi

 

But you shoshould be caution that between symbol' ['and'-F' must insert a space, if not the system will parse '[-F' as a single command, and print error MSG: [-F: Command not found

 

Besides, if you comparing two variables by using symbol '=' or '=', you have to insert empty space in both sides, or the test will failed.