Test (Unix)
test is a command-line utility found in Unix-like operating systems that evaluates conditional expressions.
Syntax
test expression
or
[ expression ]
Description
The test command evaluates the expression parameter. In some shells (such as FreeBSD sh(1)), it is actually a shell builtin, even though external version still exists. In the second form of the command, the [ ] (brackets) must be surrounded by blank spaces, this is because /bin/[ 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.
Functions
The following functions are used to construct this parameter:
-e FileName - FileName exists.
Note: All remaining functions 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 (chdir) 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 functions
Note that 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 - String1 variable is not a null string.
Number functions
Integer1 -eq Integer2 - Integer1 and Integer2 variables are algebraically equal. Any of the following comparisons can be used in place of -eq. -ne (not equal) -gt (greater than) -ge (greater or equal) -lt (less than) -le (less or equal)
Operators
These functions 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[1] 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
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