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 GNUcoreutils 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 nativeWin32ports of common GNU Unix-like utilities.[3] The test command has also been ported to the IBM i operating system.[4]
Syntax
test expression or [ expression ]
Arguments
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)
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[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.
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:
iftest!-s"$1"thenecho$1doesnotexistorisempty.
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 $1 is the empty string, the test command displays the error message:
test: argument expected.
2. To do a complex comparison, type:
if["$#"-lt2]||![-e"$1"]thenexitfi
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.
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. ISBN978-0-596-55526-9.