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 [.

Overview
The  command in Unix evaluates the   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  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  bundled in GNU coreutils was written by Kevin Braunsdorf and Matthew Bradburn. 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. The test command has also been ported to the IBM i operating system.

Syntax
or

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

For the  argument, if the specified file exists and is a directory, the   exit value indicates that the current process has permission to change   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:  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
arguments can be combined with the following operators: ! - Unary negation operator -a - Binary AND operator -o - Binary OR operator (the  operator has higher precedence than the   operator) \(Expression\) - Parentheses for grouping must be escaped with a backslash

The  and   operators, along with parentheses for grouping, are XSI extensions and are therefore not portable. In portable shell scripts, the same effect may be achieved by connecting multiple invocations of  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 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 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.