Date: Tue, 06 Apr 2010 17:18:59 +0300 From: Giorgos Keramidas <keramida@ceid.upatras.gr> To: kline@thought.org Cc: glarkin@FreeBSD.org, FreeBSD Mailing List <freebsd-questions@FreeBSD.org> Subject: Re: perl qstn... Message-ID: <874ojor7e4.fsf@kobe.laptop> In-Reply-To: <1270371713.5861.98.camel@tao.thought.org> (Gary Kline's message of "Sun, 04 Apr 2010 02:01:53 -0700") References: <20100403210610.GA4135@thought.org> <4BB8108A.9080104@FreeBSD.org> <1270371713.5861.98.camel@tao.thought.org>
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On Sun, 04 Apr 2010 02:01:53 -0700, Gary Kline <kline@thought.org> wrote:
> thanks for your url as well and the others to posted. but it seems
> like overkill since i dont need any explicit option or argument. i
> just need the script to tell me whether i have an arg or not.
> following is something i've kept in one of my junk drawers from when i
> was learning to write bourne sscripts. it uses the "$[token]" syntax
> that determines whether there are Any args on the cmdline. if not,
> the script prints a message and exits.
>
> #!/bin/sh
> if [ $# -eq 0 ]
> then
> echo "No args; need filename."
> else
> echo "$1"
> fi
>
> After a couple hours experimentation, the following does the same for my
> perl scripts:
>
>
> #!/usr/bin/perl
> $argc = @ARGV;
> if (! $argc ) {
> printf("No args; need filename.\n");
> }
> else {
> printf("%s\n", @ARGV);
> }
Yes, that's very close to the sh(1) version. Perl's behavior in this
case is described in the 'perlvar' manpage:
@ARGV The array @ARGV contains the command-line arguments intended
for the script. $#ARGV is generally the number of
arguments minus one, because $ARGV[0] is the first
argument, not the program's command name itself. See $0
for the command name.
In other words, when @ARGV appears in "scalar context" it yields the
'size' of the @ARGV array, e.g.:
% cat foo.pl
printf("%d .. args = [%s]\n", int(@ARGV), join(', ', (@ARGV)));
% perl foo.pl
0 .. args = []
% perl foo.pl 1
1 .. args = [1]
% perl foo.pl 1 2 3
3 .. args = [1, 2, 3]
So when int(@ARGV) is zero you know that there are no arguments at all.
This means you can write your sh version like this in Perl:
#!/usr/bin/perl
if (int(@ARGV) == 0) {
die "No args; at least one filename expected";
}
printf("%s\n", join(' ', (@ARGV)));
This is "good enough" as a command-line handling trick for really simple
scripts, but you should probably have a look at the Getopt::Std and the
Getopt::Long modules for longer scripts. Using them will make your
option parsing code much cleaner and easier to change in the future.
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