Re^3: eval, Read environment variable and expand using eval

There is a subtle yet important difference between defined and exists on hash and array elements. Defined will autovivify your hash element and make its value undefined.

Perhaps you meant this?

$r = (exists $ENV{INFORMIXSQLHOSTS}) ? $ENV{INFORMIXSQLHOSTS} : 'sqlho
+st')
[download]

If you want to check every possiblity this would be the best. However I usually just do the exists() check.

$r = ((exists $ENV{INFORMIXSQLHOSTS} && defined($ENV{INFORMIXSQLHOSTS}
+) && length($ENV{INFORMIXSQLHOSTS})  ) ? $ENV{INFORMIXSQLHOSTS} :  's
+qlhost'));
[download]

Comment on Re^3: eval, Read environment variable and expand using eval Select or Download Code

Replies are listed 'Best First'.
Re^4: eval, Read environment variable and expand using eval by Anonymous Monk on Feb 19, 2010 at 15:04 UTC
No, defined does not autovivify `my %f; warn snot => defined $f{snot}; warn snot => exists $f{snot}; __END__ snot at - line 3. snot at - line 4.` [download]	[reply] [d/l]
Re^5: eval, Read environment variable and expand using eval by bot403 (Beadle) on Feb 19, 2010 at 17:08 UTC
Darnit. I thought defined() autovivified simple hashes. Both exists and defined still can autovivify on deep hashes though. `#!/usr/bin/perl # use warnings; use Data::Dumper; my $h = { 'foo' => 1 }; if(exists($h->{notexist}{baz})){ } if(defined($h->{notdefined}{baz})){ } print Dumper($h); exit 0;` [download] `$VAR1 = { 'notexist' => {}, 'foo' => 1, 'notdefined' => {} };` [download]	[reply] [d/l] [select]
Re^6: eval, Read environment variable and expand using eval by ikegami (Patriarch) on Feb 19, 2010 at 21:29 UTC
Both exists and defined still can autovivify on deep hashes though. No, it's the dereference operator that does the autovivification. Any autovivification occurs before `defined` and `exists` are called. `$ perl -MData::Dumper -e'$h{notexist}{baz}; print Dumper \%h' $VAR1 = { 'notexist' => {} };` [download]	[reply] [d/l] [select]
Re^6: eval, Read environment variable and expand using eval by Anonymous Monk on Feb 19, 2010 at 17:36 UTC
no, neither exist nor define autovivify. you're treating notexist and notdefined as if they exist and are defined, therefore they are autovivified (start existing, you treat as hash, become hash) `#!/usr/bin/perl -- use strict; use warnings; use Data::Dumper; my %f; if ( $f{notexist}{baz} ) { warn 1} if ( $f{notdefined}{baz} ) { warn 1} die Dumper(\%f); __END__ $VAR1 = { 'notexist' => {}, 'notdefined' => {} };` [download]	[reply] [d/l]