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Full Discussion: Problem with pipes on infinite streams
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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LEARN ABOUT FREEBSD

atf-sh

ATF-SH(1)						    BSD General Commands Manual 						 ATF-SH(1)

NAME

     atf-sh [-s shell] -- interpreter for shell-based test programs

SYNOPSIS

     atf-sh script

DESCRIPTION

     atf-sh is an interpreter that runs the test program given in script after loading the atf-sh(3) library.

     atf-sh is not a real interpreter though: it is just a wrapper around the system-wide shell defined by ATF_SHELL.  atf-sh executes the inter-
     preter, loads the atf-sh(3) library and then runs the script.  You must consider atf-sh to be a POSIX shell by default and thus should not
     use any non-standard extensions.

     The following options are available:

     -s shell	  Specifies the shell to use instead of the value provided by ATF_SHELL.

ENVIRONMENT

     ATF_LIBEXECDIR    Overrides the builtin directory where atf-sh is located.  Should not be overridden other than for testing purposes.
     ATF_PKGDATADIR    Overrides the builtin directory where libatf-sh.subr is located.  Should not be overridden other than for testing purposes.
     ATF_SHELL	       Path to the system shell to be used in the generated scripts.  Scripts must not rely on this variable being set to select a
		       specific interpreter.

EXAMPLES

     Scripts using atf-sh(3) should start with:

	   #! /usr/bin/env atf-sh

     Alternatively, if you want to explicitly choose a shell interpreter, you cannot rely on env(1) to find atf-sh.  Instead, you have to hardcode
     the path to atf-sh in the script and then use the -s option afterwards as a single parameter:

	   #! /path/to/bin/atf-sh -s/bin/bash

ENVIRONMENT

     ATF_SHELL	  Path to the system shell to be used in the generated scripts.

SEE ALSO

     atf-sh(3)

BSD
								September 27, 2014							       BSD
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