eval '...'; die "err: $!"

[almr]

Hi, It seems concatenating to an eval-raised exception destroys it?

perl -Mstrict -we 'eval q(x=3) or die "err $!"'
# actual error destroyed

perl -Mstrict -we 'eval q(x=3) or die $!'
# actual error printed

What's going on?

[haukex]

The correct error variable to check after an eval is $@, not $! - the latter is actually empty in this particular case, but could potentially contain an error caused by a previous operation, leading to misleading results (try perl -Mstrict -we 'chdir("/foobarquz"); eval q(x=3) or die $!'). Also note perl -Mstrict -we 'eval q(x=3); die' has the same behavior as your second example, the reason is documented in die:

If LIST was empty or made an empty string, and $@ already contains an exception value (typically from a previous eval), then that value is reused after appending "\t...propagated".

[tybalt89]

Wrong var.

perl -Mstrict -we 'eval q(x=3) or die "err $@"'

Outputs:

err Can't modify constant item in scalar assignment at (eval 1) line 1
+, at EOF
Bareword "x" not allowed while "strict subs" in use at (eval 1) line 1
+.

[perlfan]

You might have cribbed that from an idiom, like: open my $fh, q{<}, $file or die $!


Updated before haukex caught my mistake.

[haukex]

You might have cribbed that from an idiom, like: open my $fh, q{<}, $file || die $!

That's not an idiom, it's wrong because of incorrect precedence: "open" Best Practices.

Also, just in case you're implying otherwise, eval or die is a decent approach to work around Bug in eval in pre-5.14.

Update: It is uncool to update a node in a way that renders replies confusing or meaningless. Mark your updates. Update 2: Now fixed.