Scalar vs. array context w/ join()

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

Why does this print out the count of the columns?

print OUT join "\t",@{$columns} "\n"; because the join prefers a scalar over an array?

print OUT join ("\t",@{$columns}). "\n";

Title edit by tye after moving out of Obfuscation (was: Not really obfuscation, but.....)

Comment on Scalar vs. array context w/ join() Select or Download Code

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(jeffa) Re: Not really obfuscation, but..... by jeffa (Bishop) on Nov 14, 2001 at 20:43 UTC
The first line has syntax error, print need's a comma or a period between } and "\n". I think you meant this: `my $columns = [ qw (one two three) ]; # sample data is GOOD print join "\t",@{$columns}. "\n"; print join ("\t",@{$columns}). "\n";` [download] I dropped OUT , because it doesn't matter if we are using STDOUT or another handle. So, the first line prints out "3" while the second line prints out the elements of $columns joined by tabs. What happened to the first line? Precendance my friend, the dot causes @{$columns} to be evaluated in scalar context, leaving join only one element to well, join: "3\n". That's why i like to use a comma instead: `print join "\t",@{$columns}, "\n";` [download] jeffa L-LL-L--L-LL-L--L-LL-L-- -R--R-RR-R--R-RR-R--R-RR F--F--F--F--F--F--F--F-- (the triplet paradiddle)	[reply] [d/l] [select]
Re: (jeffa) Re: Not really obfuscation, but..... by blakem (Monsignor) on Nov 14, 2001 at 23:40 UTC
Interesting, I hadn't realized that... This short snippet might illustrate the core issue a bit clearer. `#!/usr/bin/perl -wT use strict; my @arr = (7,8,9); print ",, => " , @arr , "\n"; # two commas print ",. => " , @arr . "\n"; # comma then dot print "., => " . @arr , "\n"; # dot then comma print ".. => " . @arr . "\n"; # two dots =OUTPUT ,, => 789 ,. => 3 ., => 3 .. => 3` [download] -Blake	[reply] [d/l]
(tye)Re2: Not really obfuscation, but..... by tye (Sage) on Nov 15, 2001 at 02:12 UTC
Note that your final example: `print join "\t",@{$columns}, "\n";` ends the output with "\t\n" instead of just "\n". Note much of a "bug" in this case, but a common mistake that can often have more serious effects. `print join("\t",@{$columns}), "\n";` - tye (but my friends call me "Tye")	[reply] [d/l] [select]