test (Unix)

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test is a command-line utility found in Unix-like operating systems that evaluates conditional expressions.

Syntax[edit]

 test expression 

or

 [ expression ] 

Description[edit]

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[edit]

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[edit]

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[edit]

 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[edit]

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[edit]

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[edit]

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[edit]

References[edit]

  1. ^ IEEE Std 1003.1, 2004, documentation for test