calling sub and returning value from the same line

mellin has asked for the wisdom of the Perl Monks concerning the following question:

I have a line of code that would need to call sub as well to return a value. So far the line only runs the sub but for some reason discards the return value. Perhaps a lot easier to explain with the actual code..

call the sub:

# give the sub two parameters, $saveOk gets then the subs return value
my $saveOk = saveFile($frontPage, $xmlPrint);
# printing the scalar below should now either give 1 or nothing
# depending wether the file got saved or not
print "$saveOk\n";

sub saveFile {

open FH, ">$_[0]" or error($!, "not able to write to file $_[0]") and 
+return undef; 
flock FH, 2; # take exclusive-lock
print FH "$_[1]"; # print to file-handle
close FH;

# if everything went fine, give 1 as an return value
1;
}
[download]

That "and return undef" does not seem to work, it still tries to flock and print to it, even though it should get out of the sub and return undef value if the file could not be opened. How exactly should i get the sub to abort and return undef without using exit?

Comment on calling sub and returning value from the same line Download Code

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Re: calling sub and returning value from the same line by jdalbec (Deacon) on Jan 09, 2005 at 20:43 UTC
Is `error()` returning a false value? That would cause the behavior you describe. Remember that `<EXPR> and <EXPR>` executes the second expression only if the first expression is true. To avoid this dependence on the return value of `error()` you could try `unless (open FH, ">$_[0]") { error($!, "not able to write to file $_[0]"); return undef; }` [download]	[reply] [d/l] [select]
Re^2: calling sub and returning value from the same line by dpuu (Chaplain) on Jan 09, 2005 at 21:00 UTC
Another alternative is to replace the "and" operator with a comma: `open FH, ">$file" or error("msg"), return undef;` [download] If you do this, you must use parentheses to call the "error" function. --Dave Opinions my own; statements of fact may be in error.	[reply] [d/l]
•Re: calling sub and returning value from the same line by merlyn (Sage) on Jan 09, 2005 at 20:36 UTC
What value does "error" return? And if you didn't think that mattered, you need to rethink what "and" is actually doing there. -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply]
Re: calling sub and returning value from the same line by borisz (Canon) on Jan 09, 2005 at 20:37 UTC
That work only if your `error` function returns a true value. Boris	[reply] [d/l]
Re: calling sub and returning value from the same line by Anonymous Monk on Jan 09, 2005 at 21:48 UTC
How about this, instead? `sub error { warn map { "$_\n" } @_; return undef; } # # and later # open FH, ">$_[0]" or return error($!, "not able to write to file $_[0]");` [download]	[reply] [d/l]
Re^2: calling sub and returning value from the same line by gaal (Parson) on Jan 09, 2005 at 22:26 UTC
`return`; is almost always preferable to `return undef;`.	[reply] [d/l] [select]