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Re: Re: Re: Line Numbers

by BrowserUk (Patriarch)
on Oct 17, 2003 at 22:37 UTC ( [id://300191]=note: print w/replies, xml ) Need Help??


in reply to Re: Re: Line Numbers
in thread Line Numbers

The problem here is that your "\n" line ending within your eval string are being interpolated before the string is eval'd. Effectively, you are double spacing your lines of code. escaping the "\n"s, make the problem go away.

P:\test>perl print __LINE__, "\n"; print __LINE__, "\n"; eval "print __LINE__,qq/\\n/; print __LINE__,qq/\\n/; die()"; print $@, "\n"; print __LINE__, "\n"; ^Z 1 2 1 2 Died at (eval 1) line 3. 7

I've fairly recently started coding my (rare) uses of eval like this.

#! perl -slw use strict; print __LINE__; print __LINE__; eval <<"EOS"; # line 1 "@{[__PACKAGE__]} eval @ line @{[__LINE__]}" warn; warn; die(); EOS print $@; print __LINE__; __END__ P:\test>junk 4 5 Warning: something's wrong at main eval @ line 6 line 1. Warning: something's wrong at main eval @ line 6 line 2. Died at main eval @ line 6 line 3. 14

This allows you to get very useful error messages from within the evals, telling you not only which line number within the eval failed and why, but also the package name and line number at which the eval is located. Not so important when the eval is in main as here, though knowing which line number is useful if there are more than one in the file, but it really comes into it's own when the eval is located in a module.


Examine what is said, not who speaks.
"Efficiency is intelligent laziness." -David Dunham
"Think for yourself!" - Abigail
Hooray!

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Re: Re: Re: Re: Line Numbers
by liz (Monsignor) on Oct 18, 2003 at 20:46 UTC
    I've fairly recently started coding my (rare) uses of eval like this.

    Hmmm... that might be a nice pragmatic module: one that steals the standard eval() and prefixes any string eval with package and line number of caller:

    use strict; use warnings; BEGIN { *CORE::GLOBAL::eval = sub {print "standard eval replaced!\n"}; } eval "print qq{Hello world!\n}"; __END__ Hello world

    Alas, it seems that the standard eval() cannot be replaced. ;-(

    Liz

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