ref: 948870cffe2572efb68ef0b3873b36238fb53263
dir: /man/2/arg/
.TH ARG 2
.SH NAME
arg \- parse program arguments
.SH SYNOPSIS
.EX
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;
.EE
.SH DESCRIPTION
.B Arg
parses a program's argument list in a traditional form,
as received from a shell or other program
(see
.IR command (2)).
The list must be passed to
.B init
to set the state for the other functions.
.PP
.B Arg
takes the first argument to be the program name.
Subsequent calls to
.B progname
return it.
.PP
Options are arguments containing one or more letters preceded by
.B \-
(dash, hyphen, minus).
The list of options ends
before the first argument that does not begin with a
.BR \- .
Option lists also end
after an argument
.BR \-\- ,
to allow programs
to accept arguments
that would otherwise look like options
(eg, file names for
.IR rm (1)
or a pattern for
.IR grep (1)).
Finally, option lists end
before an argument
.BR \- ,
which is traditionally interpreted by some commands as referring to the standard input or output
(depending on context).
.PP
Successive calls to
.B 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
.BI -f file
or
.BI -f " file" \f1).\f0
Following a call to
.BR opt ,
a call to
.BR arg
will return the rest of the current argument string if not empty,
failing that, the next argument string if any,
and otherwise
.BR nil .
.B Earg
is like
.B arg
except that if there is no argument associated
with the option, an error message is printed to
standard error, and a "\f5fail:usage\fP"
exception raised.
.B Setusage
sets the error message that will be printed in
this case (preceded by
.RB ` usage: '
and followed by a newline).
.PP
The argument list remaining after the last call to
.B opt
is returned by
.BR argv .
.SH EXAMPLE
The following Limbo program takes options
.BR b ,
.B c
and
.BR f ,
where
.B f
takes a file name argument.
.br
.ne 2i
.PP
.EX
.ps -1
.vs -1
.ta \w'12345678'u +\w'12345678'u +\w'12345678'u +\w'12345678'u +\w'12345678'u
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);
while((c := arg->opt()) != 0)
case c {
'b' => bflag = 1;
'c' => cflag = 1;
'f' => file = arg->arg();
* => sys->print("unknown option (%c)\en", c);
}
args = arg->argv();
sys->print("%s %d %d %s\en", arg->progname(), bflag, cflag, file);
for(; args != nil; args = tl args)
sys->print("%s\en", hd args);
}
.ps +1
.vs +1
.EE
.PP
When invoked as follows:
.IP
.B "prog -bc -ffile a b c"
.PP
the output is:
.IP
.EX
prog 1 1 file
a
b
c
.EE
.PP
and when invoked by:
.IP
.B "./prog -b -f file -z -- -bc"
.PP
the output is:
.IP
.EX
unknown option (z)
\&./prog 1 0 file
-bc
.EE
.SH SOURCE
.B /appl/lib/arg.b
.SH SEE ALSO
.IR sh (1),
.IR mash (1),
.IR command (2)