Re: Reopen file when contents changed?

After reading all these *very* helpful advices, here's what i've got:

use strict;
use warnings;

while()
{
   my @loads;
   my $i = my $cpuload = 0;
   open(INFIL,"< /proc/stat") || die("Unable To Open /proc/stat\n");
   <INFIL> =~ /^cpu\s+(\d+)\s+(\d+)\s+(\d+).*/;
   @loads  = ($1, $2, $3);
   sleep 1;
   seek INFIL, 0, 0;
   <INFIL> =~ /^cpu\s+(\d+)\s+(\d+)\s+(\d+).*/;
   foreach ($1, $2, $3) { $cpuload += $_ - $loads[$i++]; }
   close(INFIL);

   print "$cpuload\n";

}
[download]

Tie::File looks interesting, so that might not be the final version ;)

Thanks a lot folks!

--------------------------------
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Comment on Re: Reopen file when contents changed? Download Code

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Re^2: Reopen file when contents changed? by blazar (Canon) on Jun 07, 2005 at 15:31 UTC
`use strict; use warnings;` [download] Good! `while()` [download] I think that `while(1)` [download] is more customary. To be fair I thought yours wouldn't have worked at all, but to be sure I tried and it did! `{ my @loads; my $i = my $cpuload = 0; open(INFIL,"< /proc/stat") \|\| die("Unable To Open /proc/stat\n");` [download] I, for one (but I'm not the only one!), recommend using the three args form of open. Also, low precedence `or` is better suited for flow control and you may benefit from including `$!` in the error message. `<INFIL> =~ /^cpu\s+(\d+)\s+(\d+)\s+(\d+)./; @loads = ($1, $2, $3);` [download] This is overly complex for what it does, IMHO. I would probably do something like `my @loads = (<$fh> =~ /\d+/g)[0,1,2];` [download] instead. Of course this is not strictly equivalent to yours. Indeed it may be worth to check that the line is the correct one. In that case you may still do something like this: `local $_=<$fh>; (warn "something wrong!\n"), next unless /^cpu\b/; my @loads = (/\d+/g)[0..2];` [download] `sleep 1; seek INFIL, 0, 0; <INFIL> =~ /^cpu\s+(\d+)\s+(\d+)\s+(\d+)./; foreach ($1, $2, $3) { $cpuload += $_ - $loads[$i++]; } close(INFIL);` [download] So you want to iterate over the two lists in parallel. Now this is a situation in which some Perl6 features would turn out to be very handy! However, and this is not strictly perl-specific, instead of getting the same info twice per cycle, you may get it once only, and take a "backup" version of it to compare with.	[reply] [d/l] [select]
Re^3: Reopen file when contents changed? by calin (Deacon) on Jun 07, 2005 at 15:57 UTC
Side discussion: why `while () { ... }` [download] is interpreted as `while (1) { ... }` [download] I can't find anything relevant in perldoc perlsyn. `$ perl -MO=Deparse -e 'while () {print "tick!\n"}' while (1) { print "tick!\n"; }` [download] Update: Below is the deparse from perl 5.6.1. Above was 5.8. `$ perl561 -MO=Deparse -e 'while () {print "tick!\n"}' for (;;) { print "tick!\n"; }` [download] Update 2: See more discussion in thread while ()	[reply] [d/l] [select]