test (Unix)

test is a command-line utility found in Unix, Plan 9, and 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]

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.

The version of test bundled in GNU coreutils was written by Kevin Braunsdorf and Matthew Bradburn.^[2] The command is available as a separate package for Microsoft Windows as part of the UnxUtils collection of native Win32 ports of common GNU Unix-like utilities.^[3] The test command has also been ported to the IBM i operating system.^[4]

test expression or [ expression ]

The following arguments are used to construct this parameter. All arguments return True if the object (file or string) exists, and the condition specified is true.

For the -x argument, 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.

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)

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

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

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^[5] 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.

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

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 ] || ! [ -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.

• List of POSIX commands
• Unix shell
• find (Unix)

• Robbins, Arnold; Nelson H. F. Beebe (2005). "6.2.4 The test Command". Classic Shell Scripting: Hidden Commands that Unlock the Power of Unix. O'Reilly Media, Inc. pp. 120–128. ISBN 978-0-596-55526-9.
• Ian Shields (20 February 2007). "Linux tip: Bash test and comparison functions". IBM DeveloperWorks.
• William Shotts (2013). "27 – Flow Control: Branching With if". The Linux Command Line. No Starch Press. pp. 381–390. ISBN 978-1-59327-389-7. (free download)

The Wikibook Guide to Unix has a page on the topic of: Commands

• test – Shell and Utilities Reference, The Single UNIX Specification, Version 5 from The Open Group
• test(1) – Linux User Commands Manual
• test(1) – Plan 9 Programmer's Manual, Volume 1