Re^2: First attempt at bringing in file for input/output

It is not allowed to optionally create a variable in an if statement.

I cannot see where this is attempted; can you point this out? (I assume you're referring to the OPed code, but I can't see it anywhere in the thread.) (Update: As an aside, note that conditional creation of a variable is "allowed" in the sense that it is not a syntactic error, but it's not a good idea for reasons discussed here and documented here.)

open my $FH_infile, '<', "$in_file" or die "Can't open $in_file";

And just to satisfy my idle curiosity, can you say why you use the "$in_file" idiom (stringizing a string)? (I notice talexb also uses the idiom here.)

Give a man a fish: <%-{-{-{-<

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Re^3: First attempt at bringing in file for input/output by haukex (Archbishop) on Oct 22, 2018 at 08:23 UTC
As an aside, note that conditional creation of a variable is "allowed" in the sense that it is not a syntactic error Not really a syntax error, no, but: $ perl -wMstrict -Mdiagnostics -e 'my $x if 0' Deprecated use of my() in false conditional. This will be a fatal erro +r in Perl 5.30 at -e line 1 (#1) (D deprecated) You used a declaration similar to my $x if 0. Ther +e has been a long-standing bug in Perl that causes a lexical variabl +e not to be cleared at scope exit when its declaration includes a fa +lse conditional. Some people have exploited this bug to achieve a kin +d of static variable. Since we intend to fix this bug, we don't want p +eople relying on this behavior. You can achieve a similar static effect + by declaring the variable in a separate block outside the function, e +g sub f { my $x if 0; return $x++ } becomes { my $x; sub f { return $x++ } } Beginning with perl 5.10.0, you can also use state variables to ha +ve lexicals that are initialized only once (see feature): sub f { state $x; return $x++ } This use of my() in a false conditional has been deprecated since Perl 5.10, and it will become a fatal error in Perl 5.30. [download] See also #133543.	[reply] [d/l]

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Re^3: First attempt at bringing in file for input/output
by haukex (Archbishop) on Oct 22, 2018 at 08:23 UTC

As an aside, note that conditional creation of a variable is "allowed" in the sense that it is not a syntactic error

Not really a syntax error, no, but:

$ perl -wMstrict -Mdiagnostics -e 'my $x if 0'
Deprecated use of my() in false conditional. This will be a fatal erro
+r in Perl
    5.30 at -e line 1 (#1)
    (D deprecated) You used a declaration similar to my $x if 0.  Ther
+e
    has been a long-standing bug in Perl that causes a lexical variabl
+e
    not to be cleared at scope exit when its declaration includes a fa
+lse
    conditional.  Some people have exploited this bug to achieve a kin
+d of
    static variable.  Since we intend to fix this bug, we don't want p
+eople
    relying on this behavior.  You can achieve a similar static effect
+ by
    declaring the variable in a separate block outside the function, e
+g
    
        sub f { my $x if 0; return $x++ }
    
    becomes
    
        { my $x; sub f { return $x++ } }
    
    Beginning with perl 5.10.0, you can also use state variables to ha
+ve
    lexicals that are initialized only once (see feature):
    
        sub f { state $x; return $x++ }
    
    This use of my() in a false conditional has been deprecated since
    Perl 5.10, and it will become a fatal error in Perl 5.30.
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