Testing Files & Logical Operators

Testing Files

A useful testing feature provided by the shell is the capability to test file characteristics such as file type and permissions.

Synopsis :

test   -option   filename

Example :

$ test -f funfile
$ echo $?
0
$ test -d funfile
$ echo $?
1

Operation	Description
-d file	True if the file is a directory
-f file	True if the file exists and is a normal file (not a directory)
-s file	True if the file is more than zero bytes in length
-r file	True if the file is readable
-w file	True if the file is writable
-e file	True if the file exists
-L file	True if the file is a symbolic link
file1 -nt file2	True if file1 is newer than file2
file1 -ot file2	True if file1 is older than file2
-x file	True if the file is executable

Testing with Logical Operators

Logical operations can be performed on two expressions with one of the logical operators.

Operation	Description
expr1 -o expr2	Logical OR, true if either expr1 or expr2 is true
expr1 -a expr2	Logical AND, true if both expr1 and expr2 are true
! expr	Logical NOT, true if expr is false