Two variables changed by tr

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

Have used perl for 25 years, but after a day of contemplation still cannot figure out why use of tr changes two variables instead of one, i.e. why $char1 is being upper-cased in following

my @chars = ( 'a', 'b' ) ;
foreach my $char1 ( @chars )
{
  foreach my $char2 ( @chars )
  {
    print "BEFORE: $char1 $char2 \n" ;
    $char2 =~ tr/a-z/A-Z/ ;  # $char1 ALSO UPPER-CASED !?
    print " AFTER: $char1 $char2 \n" ;
  }
}
[download]

with output

BEFORE: a a
 AFTER: A A
BEFORE: A b
 AFTER: A B
BEFORE: B A
 AFTER: B A
BEFORE: B B
 AFTER: B B
[download]

Comment on Two variables changed by tr Select or Download Code

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Re: Two variables changed by tr by hippo (Archbishop) on Jul 03, 2024 at 18:36 UTC
`foreach` aliases into the list rather than copying. As you have 2 nested loops over the same array, half the time your two lexicals are aliases for the same item in the array. 🦛	[reply] [d/l]
Re^2: Two variables changed by tr by glendeni (Sexton) on Jul 03, 2024 at 19:45 UTC
Thanks - learned something new today	[reply]
Re^3: Two variables changed by tr by Danny (Chaplain) on Jul 04, 2024 at 13:23 UTC
Compare: `use warnings; use strict; my @chars = ( 'a', 'b' ) ; foreach my $char1 ( @chars ) { foreach my $char2 ( @chars ) { print "BEFORE: $chars[0] $chars[1] \n" ; $char2 =~ tr/a-z/A-Z/ ; # $char1 ALSO UPPER-CASED !? print " AFTER: $chars[0] $chars[1] \n" ; } }` [download]	[reply] [d/l]
Re^2: Two variables changed by tr by ikegami (Patriarch) on Jul 04, 2024 at 16:20 UTC
Example: `my @chars = qw( a b c ); for my $char ( @chars ) { $char = uc( $char ); } say "@chars"; # A B C` [download]	[reply] [d/l]