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Full Discussion: Write to file using tail -f through a pipe to grep
Top Forums UNIX for Dummies Questions & Answers Write to file using tail -f through a pipe to grep Post 302497250 by ndedhia1 on Wednesday 16th of February 2011 04:44:05 PM
Old 02-16-2011
Write to file using tail -f through a pipe to grep
Hi -- I'm looking to write to a file after piping output from tail -f through to grep:

#write to a file for all lines with "searchtext" within in error_log:

Expand|Select|Wrap|Line Numbers
  1. tail -f /var/error_log | grep searchtext > output.txt


The above command fails even though the following command::
Expand|Select|Wrap|Line Numbers
  1. tail -f /var/error_log | grep searchtext


does produce output, as expected. Nothing is getting through while redirecting to files after a tail -f... The following work:
Expand|Select|Wrap|Line Numbers
  1. tail -f /var/error_log > output.txt //without grep
  2. tail /var/error_log | grep searchtext > output.txt //without -f


So it's just the combination of grep and tail with specifically the -f (following) option that causes the problem. It would be ideal to be able to do this with a single inline command. Any ideas?

thanks for the help!!
 

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LEARN ABOUT LINUX

motd.tail

MOTD.TAIL(5)						   Debian Administrator's Manual					      MOTD.TAIL(5)

NAME

       motd.tail - Template for building the system message of the day

DESCRIPTION

       On Debian systems, the system message of the day is rebuilt at each startup, in order to display an accurate information. /etc/motd.tail is
       the file to edit permanent changes to the message of the day.

OVERVIEW

       The initiation script /etc/init.d/bootmisc.sh prepends a line containing information about the system  to  /etc/motd.tail  and  stores  the
       resulting  file in /var/run/motd. /etc/motd is a symbolic link to /var/run/motd.  This is done to prevent changes to /etc as the system can
       not assume /etc to be writable.

       Changes to /etc/motd effectively end up in a file under /var/run which will be regenerated upon reboot.

       A symbolic link to a different file, such as /etc/motd.static disables this behaviour.

FILES

       /etc/init.d/bootmisc.sh
	      The initiation script which builds /var/run/motd

       /etc/motd
	      Symbolic link to the system message of the day at /var/run/motd

       /etc/motd.tail
	      Template for building the system message of the day

       /var/run/motd
	      System message of the day file rebuilt at each computer start

SEE ALSO

       login(1), issue(5), motd(5).

Debian								    2007-04-28							      MOTD.TAIL(5)
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