Need help working with STDIN

Zio has asked for the wisdom of the Perl Monks concerning the following question:

I've been working with Perl for a few months now and have found this site to be extremely helpful. I like working with STDIN so that I can make scripts that interact with the cmd prompt. I have a very simple problem I'm trying to solve. When I use something like this...

while (<STDIN>) {
    chomp;
    print "$_\n";
}
[download]

...it does the job. But it isn't smart enough to prompt me if I forget to pipe a file into it. I'd really like some suggestions about how to check if piped data is waiting from STDIN so that I can prompt when it hasn't been called properly.

Comment on Need help working with STDIN Download Code

Replies are listed 'Best First'.
Re: Need help working with STDIN by jdporter (Paladin) on Feb 04, 2003 at 17:32 UTC
Probably the simplest thing to do is to test whether STDIN is connected to a tty, using the `-t` operator. `sub prompt { -t STDIN and print "\n? "; } while ( prompt(), defined($_=<STDIN>) ) { chomp; print "$_\n"; }` [download] jdporter The 6th Rule of Perl Club is -- There is no Rule #6.	[reply] [d/l] [select]
Re: Need help working with STDIN by pfaut (Priest) on Feb 04, 2003 at 17:39 UTC
You can use `-t STDIN` to see if input is coming from a terminal and print your prompt if it is. `sub readprompt { my $prompt = shift; print $prompt if -t STDIN; <>; } while (my $i=readprompt(">>")) { print "You said: $i\n"; }` [download] `--- print map { my ($m)=1<<hex($_)&11?' ':''; $m.=substr('AHJPacehklnorstu',hex($_),1) } split //,'2fde0abe76c36c914586c';` [download]	[reply] [d/l] [select]
Re: Need help working with STDIN by Zio (Novice) on Feb 04, 2003 at 18:11 UTC
Thanks all! The -t was the hint I needed to get things to work.	[reply]
Re: Need help working with STDIN by hardburn (Abbot) on Feb 04, 2003 at 17:29 UTC
Hrm, most nix programs will just sit there waiting for input. I think any semi-experianced nix user would expect this behavior. Just make sure you document it's behavior and let the user take care of the rest. ---- Invent a rounder wheel.	[reply]
Re: Need help working with STDIN by Anonymous Monk on Feb 05, 2003 at 04:07 UTC
before the while loop: if (-t STDIN) { do stuff if not piped a file } else { #your while loop processes piped files here while (<STDIN>) { chomp; print "$_\n"; } } chris_piechowicz@hotmail.com	[reply]