Perl try { } catch(e) { }

Superfox il Volpone has asked for the wisdom of the Perl Monks concerning the following question:

Hi there,
I am looking for a way to implement the construct:

try {
  die ("Hello world");
} catch(e) { 
  print("Exception: " $e);
}
[download]

I know this snippet from Programming Perl 4th ed,pp 329, and it works using locals:

sub try(&$) {
  my ($try, $catch) = @_;
  eval { # perl try
    &$try
  }; if($@){ # perl catch
    local $_ = $@;
    &$catch();
  }
}
sub catch(&){  $_[0]; }
[download]

And this works as try { ... } catch { print("Exception caught: $_"); };
I'd like to refer the exception with something like catch(e){ ... }.

I would prefer to avoid using any external module such as TryCatch for portability reasons.

Thanks
s.fox

Comment on Perl try { } catch(e) { } Select or Download Code

Replies are listed 'Best First'.
Re: Perl try { } catch(e) { } by Corion (Patriarch) on Mar 03, 2015 at 14:27 UTC
Have you looked at how Try::Tiny does its thing. Most likely, you can reuse that code for your implementation. Note that `catch(e)` is invalid syntax in Perl (unless you declare a parameterless function `e()`). Resorting to something like `catch my $e {` is not allowed by Perl syntax either, because the `&` prototype works its syntactical magic only when it is the first prototype character. You could use something like `catch { my $e= $@; ... }` [download] ... if you really want to rename `$@`.	[reply] [d/l] [select]
Re^2: Perl try { } catch(e) { } by Superfox il Volpone (Sexton) on Mar 03, 2015 at 15:18 UTC
Aaaaahh I think I understood now how this is supposed to work: `#!/usr/bin/env perl sub try(&$) { my ($try, $catch) = @_; eval { # perl try &$try }; if($@){ # perl catch &$catch($@); } } sub catch(&){ shift } try{ die("Frankie"); } catch { my $e = shift; print("Hello world $e\n"); }` [download] catch { ... } is invoked before the block in the try { ...}, and all it does is to return the block as a reference to the anonymous function defined by the catch block. Tricky mechanism. Thanks, s.fox	[reply] [d/l]
Re^3: Perl try { } catch(e) { } by Anonymous Monk on Mar 03, 2015 at 15:29 UTC
If you're going to use that code instead of Try::Tiny (which by the way is pure Perl and has no non-core dependencies), make sure you read the "Background" section of Try::Tiny's docs, as there are a number of issues with $@!	[reply]
Re^3: Perl try { } catch(e) { } by karlgoethebier (Abbot) on Mar 03, 2015 at 17:39 UTC
"Aaaaahh I think I understood ..." I don't (for the moment) - but i don't care about and just do: `#!/usr/bin/env perl use strict; use warnings; use Try::Tiny; try { die qq(Goodbye World!); } catch { warn $_; }; __END__` [download] Best regards, Karl ŤThe Crux of the Biscuit is the Apostropheť	[reply] [d/l]
Re^4: Perl try { } catch(e) { } by jdeguest (Sexton) on Mar 24, 2021 at 03:29 UTC
Re^5: Perl try { } catch(e) { } by haukex (Archbishop) on Mar 24, 2021 at 08:51 UTC
Some notes below your chosen depth have not been shown here
Re^4: Perl try { } catch(e) { } by karlgoethebier (Abbot) on Mar 24, 2021 at 21:44 UTC
Re: Perl try { } catch(e) { } by Anonymous Monk on Mar 03, 2015 at 17:13 UTC
"... for portability reasons." Welcome to the 21st Century, where that is no longer a valid excuse. Add the appropriate package to your deploy policy and let your configuration management solution do the rest. You do have a configuration management solution, don't you? ;)	[reply]


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