DACSEXPR(1)						       DACS Commands Manual						       DACSEXPR(1)

NAME

       dacsexpr - DACS expression language shell and interpreter

SYNOPSIS

       dacsexpr [-x] [dacsoptions[1]] [-dl] [-e expr] [-n] [-p] [-s] [-h | -help] [-test]
		[--] [filename] [script-arg...]

DESCRIPTION

       This program is part of the DACS suite.

       The dacsexpr utility evaluates DACS expressions (see dacs.exprs(5)[2]). It is often a useful aid when composing or testing expressions to
       be used in access control rules, or when debugging ACLs and configuration directives. While they continue to be referred to as
       "expressions" for historical reasons, it has become possible to write small programs, and the language can also be useful as a simple
       scripting language independent of the rest of DACS.

       If an expression is provided, it is evaluated and the result is printed to the standard output. At most one expression can be specified. If
       the -q flag is given (one of the dacsoptions[1]), nothing is printed, expression evaluation errors are suppressed, and the program
       terminates with an appropriate exit status[3]; otherwise the result is written to the standard output. If neither a -q flag is given nor
       any flag that controls the logging level, then the logging level is set to warn overriding any configuration file logging level directive;
       this behaviour is usually convenient.

       If no expression is provided, the program reads its standard input. If the input is not coming from a terminal type device, the program
       runs in "batch mode" and prompting is suppressed; otherwise, the program runs in "interactive mode". When prompted in interactive mode,
       enter help for assistance. If the readline(3)[4] functionality was configured when the program was built, command line editing and history
       are available in interactive mode.

       If the program is executed through the system's "#!" mechanism, one or more command line arguments can be given:

	   #!/usr/local/dacs/bin/dacsexpr -test
	   // expect-exact:17
	   ${x} = 17;

       Such programs always use the script file as input, therefore no expression or other file can be specified on the "#!" line.

       The Env namespace is initialized from the program's environment. For example, if the value of the environment variable LOGNAME is bobo,
       then ${Env::LOGNAME} will be instantiated with that value. Syntactically invalid variable names are silently ignored.

	   Note
	   Configuration directives and the Conf variable namespace are available only if a configuration file is processed (e.g., by giving the
	   -uj command line flag). This is relevant, for example, if the http()[5] function is called using the https scheme because proper
	   operation will require the SSL_PROG[6] directive to be configured. See dacs.conf(5)[7].

OPTIONS

       If an expression or file has not already been specified, a filename may appear as the last argument. If filename is "-", the standard input
       is read.

       -dl
	   Print debugging information to stderr.

       -e expr
	   The given expression is evaluated.

       -h
       -help
	   Display a help message and exit.

       -n
	   Do not evaluate any expressions, only check for syntax errors.

       -p
	   Print the final result to the standard output, unless it has been suppressed by -q or -n. Without this flag, the result would have to
	   be output by the program.

       -s
	   If a single expression is being evaluated from the command line or a file and the result of evaluation is a string or bstring, the
	   output will be surrounded by quotes unless this flag is specified.

       -test
	   The input is a test case. A test case consists of options followed by an expression. There can be zero or more options, one per line,
	   embedded within a // style comment:

	       { whitespace* "//" whitespace* option-name ":" option-value end-of-line }*

	   No whitespace is allowed before or after the ":". As a special case, lines having the following format are ignored:

	       whitespace* "///" .* end-of-line

	   The first non-option line terminates the options and is the first line of the expression to be evaluated.

	   Here is an example:

	       /// Test bitwise shifts
	       // expect-exact:1024
	       1 << 10

	   An option controls how the test is to be performed and gives the expected result:

	   expect:regex
	   expect-regex:regex
	       The result string must match regex. These two option names are equivalent.

	   expect-identical:string
	       The result string must match string exactly.

	   expect-exact:string
	       The result string must match string exactly, except that C-style character constants (preceded by a backslash) in string are
	       interpolated.

	   expect-code:code
	       The result code must match code, which is 0 if the result is True, 1 if the result is False, and 2 if an error occurs. If this
	       option is not given, a default code of 0 is assumed.

	   expect-type:type
	       The type of the result must match type, which can be integer, real, string, bstring, literal, or undef.

	   expect-flags:flags
	       Currently, the only recognized values for flags are rw_namespaces and ro_namespaces. The former allows the test to create or modify
	       variables in the DACS, Args, or Env namespace; by default, these namespaces are read-only. This might be useful when testing
	       from()[8], for instance, because it allows the test to set a value for ${DACS::REMOTE_ADDR}. The default behaviour can be
	       explicitly selected by specifying ro_namespaces.

	   show-result:{yes | no}
	       The result is printed to the standard output only if the option value is yes.

	   If the test fails, a descriptive message is printed to the standard error. The program's exit status will be 0 if the test was
	   successful, 1 otherwise.

	   This example should succeed without displaying the result:

	       // expect-exact:2
	       // expect-type:integer
	       /// show-result:yes
	       1 + 1

	       Note
	       The DACS distribution includes a set of test cases in the src/tests directory that can be run for regression testing (do "make
	       tests" from the src directory). Some of the functions provided by dacs.exprs(5)[2] are also used internally by DACS, so it is
	       critical that all tests are successful even for functions that are not used from the user level.

       -x
	   If this is the very first flag it indicates that dacsexpr is being executed as a script via the system's "#!" mechanism. This might be
	   useful if the program's heuristic for determining this is incorrect. The last argument must be a filename.

       --
	   This argument explicitly marks the last flag argument. A filename argument might follow.

EXAMPLES

       The following command evaluates the expression argument (note that it is a single argument to the command) and outputs the result to
       stdout:

	   % dacsexpr -e "1+1"
	   2
	   % dacsexpr -e '${Env::USER}'
	   "bobo"
	   % dacsexpr -u example.com -e '"FEDERATION_NAME=" . ${Conf::FEDERATION_NAME}'
	   "FEDERATION_NAME=EXAMPLE"
	   % dacsexpr - a b c <<HERE
	   ? print("First arg is "${Argv::1}"")
	   ? HERE
	   First arg is "a"
	   % cat ex
	   #!/usr/local/dacs/bin/dacsexpr

	   print("Argv[2] is ${Argv::2}");
	   % chmod 0755 ex
	   % ./ex foo bar baz
	   Argv[2] is bar

DIAGNOSTICS

       If an error occurs, a message may be written to stderr, depending on the logging level. In general, the program exits 0 if and only if
       everything was fine. If a command line expression is evaluated, the program exits 0 if the expression evaluates to True, 1 if it evaluates
       to False, and 2 if an error occurs. If an explicit call to exit() is made and no true error condition occurred, then the program will exit
       with the argument value.

SEE ALSO

       dacs.exprs(5)[2]

BUGS

       New and little-used features should be used with care. This advice applies to all software.

AUTHOR

       Distributed Systems Software (www.dss.ca[9])

COPYING

       Copyright2003-2012 Distributed Systems Software. See the LICENSE[10] file that accompanies the distribution for licensing information.

NOTES

	1. dacsoptions
	   http://dacs.dss.ca/man/dacs.1.html#dacsoptions

	2. dacs.exprs(5)
	   http://dacs.dss.ca/man/dacs.exprs.5.html

	3. exit status
	   http://dacs.dss.ca/man/#diagnostics

	4. readline(3)
	   http://www.freebsd.org/cgi/man.cgi?query=readline&apropos=0&sektion=3&manpath=FreeBSD+9.0-RELEASE&format=html

	5. http()
	   http://dacs.dss.ca/man/dacs.exprs.5.html#http

	6. SSL_PROG
	   http://dacs.dss.ca/man/dacs.conf.5.html#SSL_PROG

	7. dacs.conf(5)
	   http://dacs.dss.ca/man/dacs.conf.5.html

	8. from()
	   http://dacs.dss.ca/man/dacs.exprs.5.html#from

	9. www.dss.ca
	   http://www.dss.ca

       10. LICENSE
	   http://dacs.dss.ca/man/../misc/LICENSE

DACS 1.4.27b							    10/22/2012							       DACSEXPR(1)