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Top Forums Shell Programming and Scripting Script to count matched string then check again from last read position Post 302990162 by rbatte1 on Monday 23rd of January 2017 07:31:47 AM
Old 01-23-2017
An alternate may be to open the file with tail and keep it open.

What is your overall aim for this process? You might be able to:-
Code:
while read line
do
   process "$line"
done < <(tail -f $logfile)

I think that the < <(command) is a bash construct rather than sh or ksh so it depends if you have that or even if this is appropriate. This process will not end, but continue reading the log file when new records are written, so it's near-time (strictly not quite real-time)

Beware that the log file will remain open, so if you rotate your log files, you might need to use tail -F $logfile instead to open the replacement file.


Can you tell us what the point of this code is to be? There may be a simpler way that I'm not thinking of. It would be useful to know the OS version (output from uname -a) and shell that you are using.



Kind regards,
Robin
 

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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=[+]NUM output the last NUM bytes; or use -c +NUM to output starting with byte NUM of each file -f, --follow[={name|descriptor}] output appended data as the file grows; an absent option argument means 'descriptor' -F same as --follow=name --retry -n, --lines=[+]NUM output the last NUM lines, instead of the last 10; or use -n +NUM to output starting with line NUM --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); with inotify, this option is rarely useful --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 if it is inaccessible -s, --sleep-interval=N with -f, sleep for approximately N seconds (default 1.0) between iterations; with inotify and --pid=P, check process P at least once every N seconds -v, --verbose always output headers giving file names -z, --zero-terminated line delimiter is NUL, not newline --help display this help and exit --version output version information and exit NUM 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
GNU coreutils online help: <http://www.gnu.org/software/coreutils/> Report tail translation bugs to <http://translationproject.org/team/> COPYRIGHT
Copyright (C) 2017 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
head(1) Full documentation at: <http://www.gnu.org/software/coreutils/tail> or available locally via: info '(coreutils) tail invocation' GNU coreutils 8.28 January 2018 TAIL(1)
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