BEGIN and END with -p or -n

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

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Re: BEGIN and END with -p or -n by Fletch (Bishop) on Dec 01, 2005 at 05:02 UTC
What `-n` and `-p` do is wrap something like the following around your code (no, it's not the exact code; just a rough facsimile) `while( <> ) { # -e goes here } continue { print; }` [download] If you have a `BEGIN {}` or `END {}` in `awk` the code in those is run before or after the first line of input is read. So it's in effect saying you get: `## code that was in BEGIN block while( <> ) { ## -e code } continue { print; } ## code that was in END block` [download]	[reply] [d/l] [select]
Re: BEGIN and END with -p or -n by ambrus (Abbot) on Dec 01, 2005 at 08:48 UTC
What BEGIN and END really does is documented in perlsub. It wouldn't make much sense to repeat it in perlrun.	[reply]
Re^2: BEGIN and END with -p or -n by Tanktalus (Canon) on Dec 01, 2005 at 15:05 UTC
But it would make great sense that if you're going to single them out in perlrun, that you point to perlsub "for more information on how BEGIN and END work."	[reply]
Re^2: BEGIN and END with -p or -n by jmcnamara (Monsignor) on Dec 01, 2005 at 15:27 UTC
"What BEGIN and END really does is documented in perlsub". Actually perlsub points back to perlmod: The BEGIN , CHECK , INIT and END subroutines are not so much subroutines as named special code blocks, of which you can have more than one in a package, and which you can not call explicitly. See "BEGIN, CHECK, INIT and END" in perlmod -- John.	[reply]
Re: BEGIN and END with -p or -n by sauoq (Abbot) on Dec 02, 2005 at 09:22 UTC
Did anyone else read the subject of this post the way I did? -sauoq "My two cents aren't worth a dime.";	[reply]
Re^2: BEGIN and END with -p or -n by McDarren (Abbot) on Dec 02, 2005 at 10:12 UTC
heh... yes, I did a quick double-take ;)	[reply]
Re^2: BEGIN and END with -p or -n by QM (Parson) on Dec 02, 2005 at 19:54 UTC
Sorry, I missed that. I must be in Perl6 mode, as whitespace has meaning. So who's going to define that -r command so you guys can spell something more interesting? Or do we just need to use a pipe? `perl -p\|-n` [download] -QM -- Quantum Mechanics: The dreams stuff is made of	[reply] [d/l]
Re: BEGIN and END with -p or -n by jmcnamara (Monsignor) on Dec 01, 2005 at 15:43 UTC
"When you use the -n or -p switches to Perl, BEGIN and END work just as they do in awk" What confuses me about this is the corollary that without -n and -p BEGIN and END don't work as they do in awk. That is, it seems to imply that BEGIN and END work differently with -n and -p than in other cases (apart from the obvious exception of -c). Is that the case? -- John.	[reply]
Re^2: BEGIN and END with -p or -n by TimToady (Parson) on Dec 01, 2005 at 16:13 UTC
No, they work the same. It's the rest of the code that works differently, insofar as it's not inside an implicit loop any more. BEGIN and END don't care whether they're inside a loop or not, which is why they "degenerate" to the case of awk and sed when they are in an implicit loop.	[reply]
Re^3: BEGIN and END with -p or -n by QM (Parson) on Dec 02, 2005 at 04:28 UTC
So it seems that the statement in perlmod is extraneous, and should be cut, as BEGIN and END do what they do, regardless. There's no reason to mention awk, or imply a different behavior under -p or -n. -QM -- Quantum Mechanics: The dreams stuff is made of	[reply]