Altering Behavior of a Script

bichonfrise74 has asked for the wisdom of the Perl Monks concerning the following question:

I have a script called ask_input.pl which basically asked for an input. Below is the script.

#!/usr/bin/perl

use strict;

print "Enter your answer?\n";    # Line 3
<>;                              # Line 4
print "Done.\n";
[download]

So, when I call this script from the command line, it should ask for the input.

Now, when I call this script from another script or is run through the cron, it should bypass the lines where it asks for the inputs specifically lines 3 and 4. I was thinking of using GetOpt::Long to add an argument in the ask_input.pl script, and if that particular argument exists then it will just bypass lines 3 and 4.

Is this the efficient way to do this? What are the other ways of doing this? I read somewhere but could not recall that a Perl module can be run as both as a module and as a stand-alone script. I'm not sure if I can use this in this situation though.

Comment on Altering Behavior of a Script Download Code

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Re: Altering Behavior of a Script by ikegami (Patriarch) on Sep 03, 2009 at 18:15 UTC
Some times, `-t STDIN` is used. But here, arguments sound like the way to go. If "answer" is provided as an argument, use it. If not, prompt for it. PS - If you're want to be interactive, use `<STDIN>` and not `<>`.	[reply] [d/l] [select]
Re^2: Altering Behavior of a Script by ig (Vicar) on Sep 03, 2009 at 18:33 UTC
I never noticed -t. It even works on Windows!!	[reply]
Re: Altering Behavior of a Script by ig (Vicar) on Sep 03, 2009 at 18:24 UTC
If I were writing a C program on *nix I would use isatty. I have never used it but POSIX provides this function which should work if you are on a POSIX compliant system. For another idea based on stat see http://perl.plover.com/yak/commands-perl/samples/slide016.html.	[reply]
Re: Altering Behavior of a Script by bichonfrise74 (Vicar) on Sep 03, 2009 at 20:37 UTC
Hi ikegami, I was playing with the -t STDIN that you mentioned but I think I missed something. Please see below. Here's the ask_input.pl `#!/usr/bin/perl print "Enter your answer?\n"; if ( -t STDIN ) { <STDIN>; print "Terminal was used.\n"; } else { print "Not a terminal.\n"; } print "Done.\n";` [download] Here's the caller.pl `#!/usr/bin/perl use strict; system( "perl /tmp/ask_input.pl" );` [download] So, when I run caller.pl on the terminal, it will still ask for the input... but I thought it should not do this.	[reply] [d/l] [select]
Re^2: Altering Behavior of a Script by ikegami (Patriarch) on Sep 03, 2009 at 20:43 UTC
`system` doesn't mess with any of the file handles passed to the child. If caller.pl is called interactively, so is ask_input.pl. But why are you using `-t`? You need to get your answer from somewhere. You can't test if you're going to receive an answer from a terminal, so that's the last place you should check. You should base whether you prompt or not based on the presence or absence of the answer elsewhere (e.g. argument, config file).	[reply] [d/l] [select]
Re^3: Altering Behavior of a Script by bichonfrise74 (Vicar) on Sep 03, 2009 at 20:47 UTC
Ah, I see what you mean.	[reply]
Re: Altering Behavior of a Script by Bloodnok (Vicar) on Sep 03, 2009 at 19:52 UTC
On *NIX, the environment variable `$-` will contain 'i' iff the shell was invoked interactively i.e. `if ($ENV{'-'} =~ 'i') { # interactive invocation } else { # non-interactive e.g. cron, invocation }` [download] A user level that continues to overstate my experience :-))	[reply] [d/l] [select]
Re^2: Altering Behavior of a Script by bichonfrise74 (Vicar) on Sep 03, 2009 at 20:44 UTC
I'm on a Linux system, but the script you provided does not seem to be working for me. In fact, if I do this, `perl -e 'print join "\n", keys %ENV';` [download] I do not even see '-', the closest thing that would resemble this is '_'. But if I print the value of '_', it will give me this: /usr/bin/perl	[reply] [d/l]
Re^3: Altering Behavior of a Script by ikegami (Patriarch) on Sep 03, 2009 at 20:52 UTC
Bloodnok is thinking of special `bash` variable `$-`. It is not an environment variable, and it would be useless to a child anyway.	[reply] [d/l] [select]