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Top Forums Shell Programming and Scripting Setting rate of execution using while Post 302639713 by jim mcnamara on Saturday 12th of May 2012 11:23:29 PM
Old 05-13-2012
I do not see what tail gives you. But. Try this.
Code:
dt=`date`
cnt=0;
while [ $cnt -lt 1000 ]
do
   echo $dt
   cnt=$(( $cnt + 1  ))
done > dtfile

>outputfile
while :
do
  cat dtfile 
  sleep 1
done > outputfile &
sleep 1
tail -f outputfile

You may want to learn about the sync command, and how new data is written to disk periodically, not continuously.
Since the kernel keeps all of the data being written to outfile, tail -f will see it all (except the first 990 lines of outfile)
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TAIL(1) 							   User Commands							   TAIL(1)

NAME
tail - output the last part of files SYNOPSIS
tail [OPTION]... [FILE]... DESCRIPTION
Print the last 10 lines of each FILE to standard output. With more than one FILE, precede each with a header giving the file name. With no FILE, or when FILE is -, read standard input. Mandatory arguments to long options are mandatory for short options too. -c, --bytes=K output the last K bytes; alternatively, use -c +K to output bytes starting with the Kth of each file -f, --follow[={name|descriptor}] output appended data as the file grows; -f, --follow, and --follow=descriptor are equivalent -F same as --follow=name --retry -n, --lines=K output the last K lines, instead of the last 10; or use -n +K to output lines starting with the Kth --max-unchanged-stats=N with --follow=name, reopen a FILE which has not changed size after N (default 5) iterations to see if it has been unlinked or renamed (this is the usual case of rotated log files) --pid=PID with -f, terminate after process ID, PID dies -q, --quiet, --silent never output headers giving file names --retry keep trying to open a file even when it is or becomes inaccessible; useful when following by name, i.e., with --follow=name -s, --sleep-interval=N with -f, sleep for approximately N seconds (default 1.0) between iterations -v, --verbose always output headers giving file names --help display this help and exit --version output version information and exit If the first character of K (the number of bytes or lines) is a `+', print beginning with the Kth item from the start of each file, other- wise, print the last K items in the file. K may have a multiplier suffix: b 512, kB 1000, K 1024, MB 1000*1000, M 1024*1024, GB 1000*1000*1000, G 1024*1024*1024, and so on for T, P, E, Z, Y. With --follow (-f), tail defaults to following the file descriptor, which means that even if a tail'ed file is renamed, tail will continue to track its end. This default behavior is not desirable when you really want to track the actual name of the file, not the file descrip- tor (e.g., log rotation). Use --follow=name in that case. That causes tail to track the named file in a way that accommodates renaming, removal and creation. AUTHOR
Written by Paul Rubin, David MacKenzie, Ian Lance Taylor, and Jim Meyering. REPORTING BUGS
Report tail bugs to bug-coreutils@gnu.org GNU coreutils home page: <http://www.gnu.org/software/coreutils/> General help using GNU software: <http://www.gnu.org/gethelp/> Report tail translation bugs to <http://translationproject.org/team/> COPYRIGHT
Copyright (C) 2010 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. SEE ALSO
The full documentation for tail is maintained as a Texinfo manual. If the info and tail programs are properly installed at your site, the command info coreutils 'tail invocation' should give you access to the complete manual. GNU coreutils 8.5 February 2011 TAIL(1)
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