test, [, [[ -- test for condition

test, [, [[ test for condition	Command

SYNOPSIS

test expression

[ expression ]

[[ expression ]]

The test command checks for various properties of files, strings and integers. It produces no output (except error messages) but returns the result of the test as the exit status; see DIAGNOSTICS for more information.

The command line includes a Boolean expression. The simplest expression is a string which is true if the string is non-empty (that is, has non-zero length). More complex expressions are composed of operators and operands, each of which is a separate argument (that is, surrounded by white space). The operators imply the number and type of their operands. The operators taking a file operand evaluate as false (without error) if the file does not exist.

The [ command

[ expression ]

is identical to the test command

The [[ command

[[ expression ]]

features some different operators than the test and [ commands.

Operators

test, [, and [[ accept the following operators:

-b file

true if the file is a block special file

-c file

true if the file is a character special file

-d file

true if the file is a directory

-e file

true if the file exists

-f file

true if the file is an ordinary file

-g file

true if the setgid attribute of the file is on under UNIX

-h file

true if file is a symbolic link

-k file

true if the save text attribute of the file is on under UNIX

-L file

true if file is a symbolic link

-n string

true if the length of string is greater than zero

-p file

true if the file is a FIFO (named pipe)

-r file

true if the file is readable

-s file

true if the size of the file is non-zero

-t fd

true if the numeric file descriptor fd is open and associated with a terminal

-u file

true if the setuid attribute of the file is on under UNIX

-w file

true if the file is writable

-x file

true if the file is executable

-z string

true if the length of the string is zero

number1 -eq number2

true if number1 and number2 are equal

Both number1 and number2 must be integers

number1 -ge number2

true if number1 is greater than or equal to number2

number -gt number

true if number1 is greater than number2

number1 -le number2

true if the first number1 is less than or equal to number2

number1 -lt number2

true if number1 is less than number2

number1 -ne number2

true if number1 is not equal to number2

file1 -nt file2

true if file1 is newer than file2

file1 -ot file2

true if file1 is older than file2

file1 -ef file2

true if file1 has the same device and i-node number as file2

The following operators handle string comparisons for the test and [ commands:

string: true if string is not a null string
string1 = string2: true if string1 and string2 are identical
string1 != string2: true if string1 and string2 are not identical

The [[ command has several operators which handle string comparisons and pattern-matching. In the following descriptions, pattern is a glob pattern as described in the File Name Generation section of sh. To treat pattern as a string, quote it.

string == pattern
string = pattern: true if string matches pattern.
string != pattern: true if string does not match pattern.
string1 < string2: true if string1 comes before string2 alphabetically.
string1 > string2: true if string1 comes after string2 alphabetically.

The following operators allow you to combine other operators:

expr1 -a expr2 (test and [ commands)
expr1 && expr2 ([[ command): logical AND; true if both expr1 and expr2 are true
expr1 -o expr2 (test and [ commands)
expr1 || expr2 ([[ command): logical OR; true if either expr1 or expr2 is true
! expr: logical negation; true if expr is false
( expr ): binding; true if expr is true

The precedence of the operators, in descending order, is:

parenthesized expressions
unary operators
comparison operators
logical AND
logical OR

EXAMPLES

The following command reports on whether the first positional parameter contains a directory or a file:

if [ -f $1 ]
then
  echo $1 is a file
elif [ -d $1 ]
then
  echo $1 is a directory
else
  echo $1 neither file nor directory
fi

This example illustrates the use of test and is not intended to be an efficient method.

DIAGNOSTICS

Possible exit status values are:

0: The expression was true.
1: The expression was false or missing.
2: The expression was badly formed.

PORTABILITY

POSIX.2. x/OPEN Portability Guide 4.0.

The -k, -L, -nt, -ot, -ef, -a and -o operators, plus the use of parentheses to group operators together, are all extensions to the POSIX standard.

The -k, -L, -nt, -ot, and -ef operators are extensions to the x/OPEN standard.