Shell simple Use (v) three of the variables

Shell variable Handling

1. Variable deletion

${var#key} Delete the shortest match from the beginning

${var# #key} Delete the longest match from the beginning

　　

2. Variable deletion

${var%key} Delete shortest match from tail forward

${var%%key} deletes the longest match from the tail forward

　　

3. Variable substitution

${var/old/new} replaces the first match

${var//old/new} Replace all matches

　　

4. Replacing and assigning values

A. ${var-init} to variable var, existence is persisted, no then assignment init

　　

B. ${var:-init} to variable Var, a non-null value is persisted, no or null value is assigned to Init

　　

C. ${var+expr} If the variable var does not exist, it is not assigned, and if the variable var exists, the value expr

　　

D. ${var:+expr} if the variable var does not exist or is NULL, the value is not assigned, and if Var is a non-null value, expr is assigned

　　

E. ${var=expr}

　　

F. ${var:=expr}

　　

G. ${var?expr}

　　　　

H. ${var:?expr}

　　

Shell simple Use (v) three of the variables