test (Unix)

test is a command-line utility found in Unix-like operating systems that evaluates conditional expressions.

test was turned into a shell builtin command in 1981 with UNIX System III and at the same time made available under the alternate name [.[1]

Syntax

test expression

or

[ expression ]

Description

The test command in Unix evaluates the expression parameter. In most recent shell implementations, it is a shell builtin, even though the external version still exists. In the second form of the command, the [ ] (brackets) must be surrounded by blank spaces. This is because [ is a program and POSIX compatible shells require a space between the program name and its arguments. One must test explicitly for file names in the C shell. File-name substitution (globbing) causes the shell script to exit.

The test command is not to be confused with the [[ reserved word that was introduced with ksh88. The latter is not a command but part of the ksh88 syntax and does not apply file-name substitution to glob expressions.

Arguments

The following arguments are used to construct this parameter:

-e FileName - FileName exists

All remaining arguments return true if the object (file or string) exists, and the condition specified is true.

-b Filename - Returns a True exit value if the specified FileName exists and is a block special file
-c FileName - FileName is a character special file
-d FileName - FileName is a directory

-f FileName - FileName is a regular file
-g FileName - FileName's Set Group ID bit is set
-h FileName - FileName is a symbolic link
-k FileName - FileName's sticky bit is set
-L FileName - FileName is a symbolic link
-p FileName - FileName is a named pipe (FIFO)
-r FileName - FileName is readable by the current process
-s FileName - FileName has a size greater than 0
-t FileDescriptor - FileDescriptor is open and associated with a terminal
-u FileName - FileName's Set User ID bit is set
-w FileName - FileName's write flag is on. However, the FileName will not be writable on a read-only file system even if test indicates true
-x FileName - FileName's execute flag is on
If the specified file exists and is a directory, the True exit value indicates that the current process has permission to change cd into the directory.

Non standard Korn Shell extensions:

file1 -nt file2 - file1 is newer than file2
file1 -ot file2 - file1 is older than file2
file1 -ef file2 - file1 is another name for file2 - (symbolic link or hard link)

String arguments

In Perl, these sections are reversed: eq is a string operator and == is a numerical operator, and so on for the others.

-n String1 - the length of the String1 variable is nonzero
-z String1 - the length of the String1 variable is 0 (zero)
String1 = String2 - String1 and String2 variables are identical
String1 != String2 - String1 and String2 variables are not identical
String1 - true if String1 variable is not a null string

Number arguments 

Integer1 -eq Integer2 - Integer1 and Integer2 variables are algebraically equal
-ne - not equal
-gt - greater than
-ge - greater or equal 
-lt - less than
-le - less or equal

Operators

test arguments can be combined with the following operators:

! - Unary negation operator
-a - Binary AND operator
-o - Binary OR operator (the -a operator has higher precedence than the -o operator)
\(Expression\) - Parentheses for grouping must be escaped with a backslash \

The -a and -o operators, along with parentheses for grouping, are XSI extensions[2] and are therefore not portable. In portable shell scripts, the same effect may be achieved by connecting multiple invocations of test together with the && and || operators and parentheses.

Exit status

This command returns the following exit values:

0 - The Expression parameter is true
1 - The Expression parameter is false or missing
>1 - An error occurred

Examples

1. To test whether a file is nonexistent or empty, type:

 if test ! -s "$1"
 then
   echo $1 does not exist or is empty.
 fi

If the file specified by the first positional parameter to the shell procedure, $1, does not exist or is of size 0, the test command displays the message. If $1 exists and has a size greater than 0, the test command displays nothing.

Note: There must be a space between the -s function and the file name.

The quotation marks around $1 ensure that the test works properly even if the value of $1 is a null string. If the quotation marks are omitted and $1 is the empty string, the test command displays the error message:

test: argument expected.

2. To do a complex comparison, type:

 if [ $# -lt 2 -o ! -e "$1" ]
 then
   exit
 fi

If the shell procedure is given fewer than two positional parameters or the file specified by $1 does not exist, then the shell procedure exits. The special shell variable $# represents the number of positional parameters entered on the command line that starts this shell procedure.

See also

References

  1. ↑ http://www.in-ulm.de/~mascheck/bourne/#system3 Bourne Shell changes with System III
  2. ↑ IEEE Std 1003.1, 2004, documentation for test

Further reading

External links


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