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Re: How to trace a dying process

by Roger (Parson)
on Sep 06, 2003 at 13:59 UTC ( #289462=note: print w/replies, xml ) Need Help??


in reply to How to trace a dying process

The while loop is a gotcha in Perl sometimes. Consider the loop
while (<>) { ... }
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 <>) { ... }
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.

Replies are listed 'Best First'.
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 $_"; }
    1 got 1 2 got 2 0 got 0 5 got 5
    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.

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...

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