ARG(2) ARG(2)
NAME
arg - parse program arguments
SYNOPSIS
include "arg.m";
arg := load Arg Arg->PATH;
init: fn(argv: list of string);
setusage: fn(s: string);
usage: fn();
progname: fn(): string;
opt: fn(): int;
arg: fn(): string;
earg: fn(): string;
argv: fn(): list of string;
DESCRIPTION
Arg parses a program's argument list in a traditional form,
as received from a shell or other program (see command(2)).
The list must be passed to init to set the state for the
other functions.
Arg takes the first argument to be the program name. Subse-
quent calls to progname return it.
Options are arguments containing one or more letters pre-
ceded by - (dash, hyphen, minus). The list of options ends
before the first argument that does not begin with a -.
Option lists also end after an argument --, to allow pro-
grams to accept arguments that would otherwise look like
options (eg, file names for rm(1) or a pattern for grep(1)).
Finally, option lists end before an argument -, which is
traditionally interpreted by some commands as referring to
the standard input or output (depending on context).
Successive calls to opt return option characters in turn; 0
is returned at the end of the list. A program might take a
parameter to a given option (eg, an option of the form
-ffile or -f file). Following a call to opt, a call to arg
will return the rest of the current argument string if not
empty, failing that, the next argument string if any, and
otherwise nil. Earg is like arg except that if there is no
argument associated with the option, an error message is
printed to standard error, and a "fail:usage" exception
raised. Setusage sets the error message that will be
printed in this case (preceded by `usage:' and followed by a
newline).
The argument list remaining after the last call to opt is
returned by argv.
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ARG(2) ARG(2)
EXAMPLE
The following Limbo program takes options b, c and f, where
f takes a file name argument.
implement Prog;
include "sys.m";
sys: Sys;
include "draw.m";
include "arg.m";
arg: Arg;
Prog: module
{
init: fn(nil: ref Draw->Context, nil: list of string);
};
init(nil: ref Draw->Context, args: list of string)
{
sys = load Sys Sys->PATH;
arg = load Arg Arg->PATH;
bflag := cflag := 0;
file := "";
arg->init(args);
arg->setusage("prog [-bc] [-f file] args ...");
while((c := arg->opt()) != 0)
case c {
'b' => bflag = 1;
'c' => cflag = 1;
'f' => file = arg->earg();
* =>
sys->print("unknown option (%c)\n", c);
arg->usage();
}
args = arg->argv();
sys->print("%s %d %d %s\n", arg->progname(), bflag, cflag, file);
for(; args != nil; args = tl args)
sys->print("%s\n", hd args);
}
When invoked as follows:
prog -bc -ffile a b c
the output is:
prog 1 1 file
a
b
c
and when invoked by:
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ARG(2) ARG(2)
./prog -b -f file -z -- -bc
the output is:
unknown option (z)
./prog 1 0 file
-bc
SOURCE
/appl/lib/arg.b
SEE ALSO
sh(1), mash(1), command(2)
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