qw() problem

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

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Re: qw() problem by muntfish (Chaplain) on Oct 10, 2005 at 11:47 UTC
You should have a look at perlop, specifically the section called "Quote and quote-like operators". This should explain `qw` etc. I'm not 100% sure exactly what you're trying to achieve. Are you trying to make an array from the scalar value `$all` ? If so then split is your friend: `$all = "name1 name2 name3"; @arr = someFunc(@dd, split(/ /, $all));` [download] s^^unp(;75N=&9I<V@`ack(u,^;s\|$.+\`\|"$`$'\"$&\"$"\|ee;/m.+h/&&print$&	[reply] [d/l] [select]
Re^2: qw() problem by Zaxo (Archbishop) on Oct 10, 2005 at 12:44 UTC
It doesn't matter with this $all, but there is a magical split which splits on all whitespace and trims any off the ends. It's triggered by using a quoted single space as the first argument. `my @arr = someFunc( @dd, split ' ', $all);` [download] The action of magical split on a variable is very like that of qw on its literal argument. `my @args = qw/ name1 name2 name3 /; my $all = "\n name1\n name2\n name3\n"; my @arr = split ' ', $all;` [download] After Compline, Zaxo	[reply] [d/l] [select]
Re^2: qw() problem by jeanluca (Deacon) on Oct 10, 2005 at 12:22 UTC
split works!!!, thanks!	[reply]
Re: qw() problem by Skeeve (Parson) on Oct 10, 2005 at 11:53 UTC
qw stands for "quote words". So `qw(name1, name2, name3)` is equivalent to `('name1,', 'name2,', 'name3')` `$\=~s;s.;q^\|D9JYJ^^qq^\//\\\///^;ex;print`	[reply] [d/l] [select]
Re^2: qw() problem by gargle (Chaplain) on Oct 10, 2005 at 12:00 UTC
HI, careful with those comma's: `perl -e '@a = qw(a, b, c);map { print "$_\n"; } @a'` [download] gives: `a, b, c` [download] While: `perl -e '@a = qw(a b c);map { print "$_\n"; } @a'` [download] gives: `a b c` [download] With qw you can skip the comma... UPDATE: sorry for the spelling mistake. It's commas! I've been reading slashdot too much lately. -- if ( 1 ) { $postman->ring() for (1..2); }	[reply] [d/l] [select]
Re^3: qw() problem by Skeeve (Parson) on Oct 10, 2005 at 12:06 UTC
Not can skip but (in most cases) should skip. OTOH: You should have replied to the OP. I know of that fact, that's why I said that it's equivalent to `('name1,', 'name2,', 'name3')` [download] and not `('name1', 'name2', 'name3')` [download] Update: Just a side note ;-) Careful with those apostrophes! Generally there is no such thing as a plural apostrophe in ~~any language I know of~~ english and german. So it should be "commas" not "comma's" ;-) Update 2: Thanks to Perl Mouse I've learnd that the dutch language has a plural apostrophe in some cases. That's the reason for the correction above... `$\=~s;s.;q^\|D9JYJ^^qq^\//\\\///^;ex;print`	[reply] [d/l] [select]
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Re: qw() problem by Zaxo (Archbishop) on Oct 10, 2005 at 13:20 UTC
Split, already mentioned, is the correct solution. It's possible to coerce qw// to work on a variable using stringy eval. Your unexpected behavior happens because qw , like q, does not interpolate variables before acting. You can fake it by including the 'qw' as part of a string in an interpolating quote, `my $all = "\nname1 name2\n name3"; my @arr = someFunc(@dd, eval "qw/$all/";` [download] That's not a recommended way to do it, but it's good to know about. It's sometimes desirable to do that when the arguments of tr/// are not known in advance. After Compline, Zaxo	[reply] [d/l]
Re^2: qw() problem by Vynce (Friar) on Oct 10, 2005 at 21:03 UTC
it's worth noting that using qw"$foo" also doesn't work, as much as you might want it to.	[reply]