Ubuntu Manpage: dacsexpr - DACS expression language shell and interpreter

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.

       A script can be executed through the system's "#!" mechanism:

           #!/usr/local/dacs/bin/dacsexpr

           printf("%s\n", "Hello, world.")

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

       Command line arguments can be passed to a script. If dig-it contains:

           #!/usr/local/dacs/bin/dacsexpr

           if (${Argv::#} != 3) {
             printf("Usage: dig-it digest-name msg\n");
             exit(1);
           }

           printf("%s\n", digest(${Argv::2}, 0, ${Argv::1}));

       then running the script produces:

           % ./dig-it sha3-224 mymsg
           88fdaa49d0371a79efa2d6e8a55d27d62cd39ad393309d9a18665763

       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.

       An empty Expr namespace is created. In interactive use, the prompt string can be changed by assigning a
       string to ${Expr::prompt} and the continuation prompt can be changed by setting ${Expr::prompt2}.

           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:

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

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.

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

       Copyright © 2003-2018 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)
           https://www.freebsd.org/cgi/man.cgi?query=readline&apropos=0&sektion=3&manpath=FreeBSD+10.3-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