Re^2: Multiple foreach loops in single statement

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Re^3: Multiple foreach loops in single statement by Athanasius (Archbishop) on Oct 24, 2012 at 04:11 UTC
...we can provide a list too in split function. Sorry, no. split operates on a single string (a scalar), but not on a list: `13:57 >perl -wE " $s = q[abc]; $t = q[mno]; say for split(//, $s, $t); + " Argument "mno" isn't numeric in split at -e line 1. a b c 14:06 >perl -wE " $s = q[abc]; $t = q[mno]; say for split(//, ($s, $t) +); " Useless use of a variable in void context at -e line 1. m n o 14:06 >perl -wE " @u = (q[abc], q[mno]); say for split(//, @u); " 2 14:06 >` [download] The docs however mention EXPR ... which I assumed to be a scalar. Yes, your original assumption was correct. But `split` returns a list, which is why the output of `split` can be the subject of a `foreach` or a `map`. Hope that helps, Athanasius <°(((>< contra mundum	[reply] [d/l]
Re^4: Multiple foreach loops in single statement by gurpreetsingh13 (Scribe) on Oct 24, 2012 at 14:51 UTC
I considered myself to have given a good start on perl(as it was in some other languages)....but the wisdom of monks here and my weakness in basics shows there is still a long way to go and a lot to know.... Thanks for your help. :)	[reply]
Re^4: Multiple foreach loops in single statement by gurpreetsingh13 (Scribe) on Oct 24, 2012 at 13:22 UTC
No. See it clearly. perl -e '@lines=`cat file.pl`;print $#lines,"\n", $lines[2];' [download] Output: `18 use Unicode::Collate::Locale;` [download] this returns a list infact - a list of strings after pumping in entire file splitted on newline. And we are providing this list in place of an EXPR in split which makes it a point that we can provide a list too instead of a string.	[reply] [d/l] [select]
Re^5: Multiple foreach loops in single statement by Anonymous Monk on Oct 24, 2012 at 13:30 UTC
No , split doesn't work with lists, it forces scalar context on EXPR, so qx returns a STRING, not a list `$ perl -wle " print for split //, @ARGV " asdf 1 $ perl -wle " print for split //, @ARGV " a s d f 4 $ perl -wle " print for split //, $ARGV[0] " asdf a s d f` [download] See Tutorials: Context in Perl: Context tutorial, "List" Is a Four-Letter Word, Easy Reference for Contexts	[reply] [d/l]
Re^5: Multiple foreach loops in single statement by Athanasius (Archbishop) on Oct 24, 2012 at 13:56 UTC
gurpreetsingh13, I understand your reasoning, and for most languages you would be correct. But Perl is different: in Perl, the behaviour of functions and operators depends on context. For example, here is what the documentation says about backticks: The collected standard output of the command is returned ... In scalar context, it comes back as a single (potentially multi-line) string, or undef if the command failed. In list context, returns a list of lines ..., or an empty list if the command failed. So, in your script: perl -e 'print chr(ord()+1) foreach(split //,`cat file.pl`);' [download] the expression `cat file.pl` is in scalar context (because `split` expects a scalar expression here), so the output of the `cat` command is fed to `split` as a single, multi-line string. But in your other script: perl -e '@lines=`cat file.pl`;print $#lines,"\n", $lines[2];' [download] the assignment to an array (`@lines`) puts `cat file.pl` into list context, so the output of the `cat` command is here not a single string as before, but rather a list of strings (one for each line). Context is a central concept in Perl. You can read up on it in the references given by Anonymous Monk, above, or in Chapter 2 of Programming Perl by Christiansen, foy, and Wall (in the section beginning on page 76 of the 4^th Edition). Hope that helps, Athanasius <°(((>< contra mundum	[reply] [d/l] [select]
Re^5: Multiple foreach loops in single statement by ikegami (Patriarch) on Mar 02, 2013 at 22:54 UTC
`split`'s second argument is evaluated in scalar context, so it's more like my $output = `cat file.pl`; [download] than my @output = `cat file.pl`; [download]	[reply] [d/l] [select]