Path: utzoo!attcan!uunet!decwrl!elroy.jpl.nasa.gov!jpl-devvax!lwall
From: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Newsgroups: comp.lang.perl
Subject: Re: Deleting (Only) First Blank Line in File
Message-ID: <8567@jpl-devvax.JPL.NASA.GOV>
Date: 2 Jul 90 17:04:03 GMT
References: <1651@fallst.UUCP> <1990Jun30.214249.15211@iwarp.intel.com> <EMV.90Jul1175629@urania.math.lsa.umich.edu>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Distribution: comp
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 41

In article <EMV.90Jul1175629@urania.math.lsa.umich.edu> emv@math.lsa.umich.edu (Edward Vielmetti) writes:
: In article <1990Jun30.214249.15211@iwarp.intel.com> merlyn@iwarp.intel.com (Randal Schwartz) writes:
: 
:    | Solutions other than those using 'perl' are preferred.
: 
:    But, since you didn't say *necessary*, how about:
: 
:    perl -ne 'print unless /^$/ && $once++;'
: 
: hm, nice.  how about this problem: printing the first 10 lines after
: a signal line?  I would think it could be done with the .. operator, namely
: 
: 	perl -ne 'if (/===/) {$l = $. + 10 ;} ; if (/===/ .. $l) {print;} '
: 
: but this prints only the === line and the one following.  a test with digits
: shows that it works as expected for this:
: 
: 	perl -ne 'if (/===/) {$l = $. + 10 ;} ; if (/===/ .. 50) {print;} '
: 
: which lead me to experiment with the following which worked
: 
: 	perl -ne 'if (/===/) {$l = $. + 10 ;} ; eval "if (/===/ .. $l) {print;}"; '
: 
: the eval appears to be neccesary in order to force the .. to be
: interpreted in a scalar context, but I guess I don't really understand
: the man page, & in retrospect a simple loop would have done the trick
: OK.

The eval doesn't force a scalar context--it forces $l to be a static literal.
The arguments to .. are ordinarily interpreted as *boolean expressions*.
However

    If either operand of scalar .. is static, that operand is implicitly
    compared to the $. variable, the current line number.

So /===/ .. 50 is interpreted as /===/ .. ($. == 50).  But /===/ .. $l isn't.

The scalar .. is in there mostly to emulate sed.  Myself, I'd probably
go ahead and write a loop too.

Larry