wait for the system command to complete process

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

Hi,
Below code reads the output of the nmon system command. the script starts executes before system command complete its processing and parsing only half of the file.
Is there any work around other than using sleep command ?

 

my $result= `nmon -F file.out -s3 -c1`;

open(FILE,"<file.out") || die $!;

while(<FILE>) { print $_; } 

close(FILE);
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Re: wait for the system command to complete process by kcott (Archbishop) on Sep 13, 2012 at 05:29 UTC
G'day kulls, I'm not an `nmon` user and I don't have it installed so I can't test any of the following. My understanding is that `nmon` starts a daemon so the command will return before the daemon finishes. That would be why you're only getting part of the output. You don't show any use of `$result`: I suspect system would be a better choice than backticks. If you are only running it for a few seconds (`-s3 -c1`), then sleep may be a viable option; however, I'd probably lean more towards tailing `file.out` - File::Tail may be helpful for that. -- Ken	[reply] [d/l] [select]
Re: wait for the system command to complete process by flexvault (Monsignor) on Sep 13, 2012 at 13:54 UTC
kulls, I'm not sure I understand the problem, but I ran your code and it finished as fast as I typed the command. So if you use 'system': my $result = system(`nmon -F file.out -s3 -c1`); [download] 'system' will wait until the command completes and returns. Hope it helps...Ed "Well done is better than well said." - Benjamin Franklin	[reply] [d/l]