true(1) General Commands Manual true(1)NAME
true, false - Returns a standard exit value
SYNOPSIS
true
false
STANDARDS
Interfaces documented on this reference page conform to industry standards as follows:
true: XCU5.0
false: XCU5.0
Refer to the standards(5) reference page for more information about industry standards and associated tags.
DESCRIPTION
The true command returns a 0 (zero) exit value. The false command returns a nonzero exit value. These commands are usually used in input to
shell commands.
NOTES
The special built-in utility : (colon) is sometimes more efficient than the true command.
EXIT STATUS
[Tru64 UNIX] The nonzero value returned by the false command may vary from system to system.
EXAMPLES
To construct a loop in a shell procedure, enter: while true do date sleep 60 done
This procedure displays the date and time once a minute. To stop it, press the Interrupt key sequence.
SEE ALSO
Commands: csh(1), ksh(1), Bourne Shell sh(1b), POSIX shell sh(1p)
Standards: standards(5)true(1)
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test(1) General Commands Manual test(1)NAME
test, [ - Evaluates conditional expressions
SYNOPSIS
test [expression]
[[expression]]
STANDARDS
Interfaces documented on this reference page conform to industry standards as follows:
test: XCU5.0
[: XCU5.0
Refer to the standards(5) reference page for more information about industry standards and associated tags.
OPTIONS
None
OPERANDS
The expression to be evaluated as true or false. This expression is constructed from the operators and elements explained in the DESCRIP-
TION section.
DESCRIPTION
The test command evaluates an expression constructed of functions and operators. If the value of expression is true, test returns an exit
value of zero(0); otherwise, it returns FALSE, a nonzero exit value. The test command also returns a nonzero exit value if there are no
arguments.
The alternate form of the command surrounds expression with brackets ([ ]). When you use this form, you must surround the brackets with
spaces.
The test Expressions
All of the listed functions and operators are separate arguments to test.
The following functions are used to construct expression: TRUE if file exists and has read permission. TRUE if file exists and has write
permission. TRUE if file exists and has execute permission. TRUE if file exists and is a regular file. TRUE if file exists and is a
directory. TRUE if file exists. TRUE if file exists and is a character-special file. TRUE if file exists and is a block-special file.
TRUE if file exists and is a named pipe (FIFO). [Tru64 UNIX] TRUE if file exists and is a soft link. Synonym for -L expression. TRUE if
file exists and is a soft link. Synonym for -h expression. TRUE if file exists and its set-user ID bit is set. TRUE if file exists and
its set-group ID bit is set. [Tru64 UNIX] TRUE if file exists and its sticky bit is set. TRUE if file exists and has a size greater than
zero(0). TRUE if the open file with file descriptor number file_descriptor (1 by default) is associated with a terminal device. TRUE if
the length of string1 is zero(0). TRUE if the length of string1 is nonzero. TRUE if string1 and string2 are identical. TRUE if string1
and string2 are not identical. TRUE if string1 is not the null string. TRUE if the integers number1 and number2 are algebraically equal.
Any of the comparisons -ne, -gt, -ge, -lt, and -le can be used in place of -eq.
The listed functions can be combined with the following operators: Unary negation operator. Binary AND operator. Binary OR operator (the
-a operator has higher precedence than the -o operator). [Tru64 UNIX] Parentheses for grouping.
EXIT STATUS
The following exit values are returned: The test command evaluated expression and its value is TRUE. The test command evaluated expression
and is value is FALSE, or there are no arguments. An error occurred.
EXAMPLES
To test whether a file exists and is not empty, enter: 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 does not exist, this displays an error message. If
$1 exists, it displays nothing. There must be a space between -s expression and the file name.
The double quotes around $1 ensure that the test will work properly even if the value of $1 is the empty string. If the double
quotes are omitted and $1 is the empty string, test displays the error message test: parameter expected. To do a complex compari-
son, enter: if [ $# -lt 2 -o ! -s "$1" ] then exit fi
If the shell procedure was given fewer than two positional parameters or the file specified by $1 does not exist, then this exits
the shell procedure. The special shell variable $# represents the number of positional parameters entered on the command line that
started this shell procedure.
ENVIRONMENT VARIABLES
The following environment variables affect the execution of test: Provides a default value for the internationalization variables that are
unset or null. If LANG is unset or null, the corresponding value from the default locale is used. If any of the internationalization vari-
ables contain an invalid setting, the utility behaves as if none of the variables had been defined. If set to a non-empty string value,
overrides the values of all the other internationalization variables. Determines the locale for the interpretation of sequences of bytes
of text data as characters (for example, single-byte as opposed to multibyte characters in arguments). Determines the locale for the for-
mat and contents of diagnostic messages written to standard error. Determines the location of message catalogues for the processing of
LC_MESSAGES.
SEE ALSO
Commands: csh(1), find(1), ksh(1), Bourne shell sh(1b), POSIX shell sh(1p)
Standards: standards(5)test(1)