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Top Forums Shell Programming and Scripting Problem with pipes on infinite streams Post 302408049 by alister on Saturday 27th of March 2010 11:51:15 PM
Old 03-28-2010
You can run the stream generator in the background, asynchronously, and use a named pipe to communicate with it:
Code:
mkfifo sg_pipe
stream_generator > sg_pipe &
head -n1 sg_pipe
kill %?stream

Regards,
Alister

---------- Post updated at 10:51 PM ---------- Previous update was at 10:38 PM ----------

For the example code you used in your original post:
Code:
#!/bin/bash
counter() {
  seq 1000 | while read NUM; do
    echo $NUM
    echo "debug: $NUM" >&2 
    sleep 0.1 # slow it down so we know when this loop really ends
  done
}

mkfifo p
counter | grep --line-buffered "[27]" > p &
head -n1 p
kill %?counter

Outputs:
Code:
$ ./tokland.sh 
debug: 1
debug: 2
2

Alister
 

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IO::Async::Timer::Absolute(3pm) 			User Contributed Perl Documentation			   IO::Async::Timer::Absolute(3pm)

NAME
"IO::Async::Timer::Absolute" - event callback at a fixed future time SYNOPSIS
use IO::Async::Timer::Absolute; use POSIX qw( mktime ); use IO::Async::Loop; my $loop = IO::Async::Loop->new; my @time = gmtime; my $timer = IO::Async::Timer::Absolute->new( time => mktime( 0, 0, 0, $time[4]+1, $time[5], $time[6] ), on_expire => sub { print "It's midnight "; $loop->stop; }, ); $loop->add( $timer ); $loop->run; DESCRIPTION
This subclass of IO::Async::Timer implements one-shot events at a fixed time in the future. The object waits for a given timestamp, and invokes its callback at that point in the future. For a "Timer" object that waits for a delay relative to the time it is started, see instead IO::Async::Timer::Countdown. EVENTS
The following events are invoked, either using subclass methods or CODE references in parameters: on_expire Invoked when the timer expires. PARAMETERS
The following named parameters may be passed to "new" or "configure": on_expire => CODE CODE reference for the "on_expire" event. time => NUM The epoch time at which the timer will expire. Once constructed, the timer object will need to be added to the "Loop" before it will work. Unlike other timers, it does not make sense to "start" this object, because its expiry time is absolute, and not relative to the time it is started. AUTHOR
Paul Evans <leonerd@leonerd.org.uk> perl v5.14.2 2012-10-24 IO::Async::Timer::Absolute(3pm)
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