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 file2file1 -ot file2 - file1 is older than file2file1 -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 identicalString1 != String2 - String1 and String2 variables are not identicalString1 - 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-aoperator has higher precedence than the-ooperator)\(Expression\) - 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 true1 - 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. fiIf 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 fiIf 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.
