[Melbourne-pm] The magic of shebang (was Re: programming tutorials: Perl)

[Alec Clews]

Sorry -- correction below

On Mon, 2010-11-15 at 17:09 +1100, Alec Clews wrote:

> On Mon, 2010-11-15 at 16:48 +1100, john thornton wrote: 
> 
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> > 
> > Thanks very much for that. I went to the site and downloaded the perl
> > training book. Perldocs...so many.
> > 
> > The only part that confuses me is that if
> > 
> > # is a comment
> > 
> > then why does the shebang line have any influence:
> > 
> > #!/usr/bin/perl
> > 
> > or as a variant to show warnings for code
> > 
> > #!/usr/bin/perl -w
> > 
> > I am using to using # to "comment out" configuration files in Linux
> > for setting up mysql and so on.
> 
> 
> the shebang notation (#!) is specific to UNIX (and hence Linux)
> 
> The #! is actually interpreted by the kernel and tells it which
> interpreter to use (in this case Perl)
> 
> Perl ignores the line[1]
> 
> See also http://en.wikipedia.org/wiki/Shebang_(Unix)
> 
> 
> [1] That was a lie. As a special case Perl will look at the line and
> use any flags it sees. e.g.
> 
> #!/bin/env perl -p

#! /usr/bin/env perl -p

NB using this form of shebang is (supposedly) more portable, although I
have had problems on some systems....


> 
> will switch on the pseudo sed mode
> 
> 
> -- 
> Alec Clews
> Personal <alec.clews at gmail.com>                  Melbourne, Australia.
> Jabber:  alecclews at jabber.org.au           PGPKey ID: 0x9BBBFC7C
> Blog  http://alecthegeek.wordpress.com/
> 
> _______________________________________________
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-- 
Alec Clews
Personal <alec.clews at gmail.com>                  Melbourne, Australia.
Jabber:  alecclews at jabber.org.au           PGPKey ID: 0x9BBBFC7C
Blog  http://alecthegeek.wordpress.com/
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