shell 的if 判断

String, Integer, and File Testing

Test Operator	Test For
String Test
string1 = string2	String1 is equal to String2 (space surrounding = required)
string1 != string2	String1 is not equal to String2 (space surrounding != required)
string	String is not null
–z string	Length of string is zero
–n string	Length of string is nonzero
	EXAMPLE test -n $word or [ -n $word ] test tom = sue or [ tom = sue ]
Integer Test
int1 –eq int2	Int1 is equal to int2
int1 –ne int2	Int1 is not equal to int2
int1 –gt int2	Int1 is greater than int2
int1 –ge int2	Int1 is greater than or equal to int2
int1 –lt int2	Int1 is less than int2
int1 –le int2	Int1 is less than or equal to int2
Logical Test
expr1 -a expr2	Logical AND
expr1 -o expr2	Logical OR
! expr	Logical NOT
File Test
–b filename	Block special file
–c filename	Character special file
–d filename	Directory existence
–f filename	Regular file existence and not a directory
–g filename	Set-group-ID is set
–k filename	Sticky bit is set
–p filename	File is a named pipe
–r filename	File is readable
–s filename	File is nonzero size
–u filename	Set-user-ID bit is set
–w filename	File is writable
–x filename	File is executable