Re: How to trace a dying process

The while loop is a gotcha in Perl sometimes. Consider the loop

while (<>)
{
   ...
}
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It will work most of the time, terminating when '<>' fails with undef (reaches the end of file). However when the while loop encounters a '0' by itself, it would fail as well (while loop fails on undef or '0').

The while loop can be fix with the following:

while (defined <>)
{
  ...
}
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This while loop will only quit when the input stream really ends.

Now that comes to the second part of the problem, EOF's (^Z or ^D) encountered in the input stream unexpectedly. Perhaps you could switch from the while(){} loop to a do {} while () loop, and print out the input to a log file. Then you have a better chance of catching the error.

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Re: Re: How to trace a dying process by ctilmes (Vicar) on Sep 06, 2003 at 14:23 UTC
Works fine for me: `while (<>) { print "got $_"; }` [download] `1 got 1 2 got 2 0 got 0 5 got 5` [download] Update: see perlop2: In these loop constructs, the assigned value (whether assignment is automatic or explicit) is then tested to see if it is defined. The defined test avoids problems where line has a string value that would be treated as false by perl e.g. ``'' or ``0'' with no trailing newline.	[reply] [d/l] [select]
Re: Re: How to trace a dying process by Notromda (Pilgrim) on Sep 08, 2003 at 23:35 UTC
This begs an interesting question: how to detect a ^Z or ^D in a line...	[reply]