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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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shells(4)							   File Formats 							 shells(4)

NAME
shells - shell database SYNOPSIS
/etc/shells DESCRIPTION
The shells file contains a list of the shells on the system. Applications use this file to determine whether a shell is valid. See getuser- shell(3C). For each shell a single line should be present, consisting of the shell's path, relative to root. A hash mark (#) indicates the beginning of a comment; subsequent characters up to the end of the line are not interpreted by the routines which search the file. Blank lines are also ignored. The following default shells are used by utilities: /bin/bash, /bin/csh, /bin/jsh, /bin/ksh, /bin/pfcsh, /bin/pfksh, /bin/pfsh, /bin/sh, /bin/tcsh, /bin/zsh, /sbin/jsh, /sbin/sh, /usr/bin/bash, /usr/bin/csh, /usr/bin/jsh, /usr/bin/ksh, /usr/bin/pfcsh, /usr/bin/pfksh, /usr/bin/pfsh, and /usr/bin/sh, /usr/bin/tcsh, /usr/bin/zsh. Note that /etc/shells overrides the default list. Invalid shells in /etc/shells may cause unexpected behavior (such as being unable to log in by way of ftp(1)). FILES
/etc/shells lists shells on system SEE ALSO
vipw(1B), ftpd(1M), sendmail(1M), getusershell(3C), aliases(4) SunOS 5.10 4 Jun 2001 shells(4)
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