I've got a program which write a log to foo.log, and I want to watch
the contents of that file; tail -f would work fine, but for one
hitch.  Each time the program restarts, it closes the log file, moves
the old log to foo.log.bak, and starts a new foo.log.

I know some tails have a -F which does exactly that, but I'm on
solaris, and the solaris tail doesn't support -F.  Is there a simple
way to fake this out on solaris?

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On 14 Dec 2004 11:14:19 -0500, Roy Smith
<roy@panix.com> wrote:
> I've got a program which write a log to foo.log, and I want to watch
> the contents of that file; tail -f would work fine, but for one
> hitch.  Each time the program restarts, it closes the log file, moves
> the old log to foo.log.bak, and starts a new foo.log.
>
> I know some tails have a -F which does exactly that, but I'm on
> solaris, and the solaris tail doesn't support -F.  Is there a simple
> way to fake this out on solaris?

Use a crontab to check the size, mtime, and/or inode number of foo.log;
have it restart your script if the inode changes or the size decreases.


--
cowsay -b "Prepare to be assimoolated! "

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Roy Smith wrote:
> I've got a program which write a log to foo.log, and I want to watch
> the contents of that file; tail -f would work fine, but for one
> hitch.  Each time the program restarts, it closes the log file, moves
> the old log to foo.log.bak, and starts a new foo.log.
>
> I know some tails have a -F which does exactly that, but I'm on
> solaris, and the solaris tail doesn't support -F.  Is there a simple
> way to fake this out on solaris?

You could do something like this (untested):

_file="$1"
_start=0
while :
do
_end=`wc -l < "$_file"`
_end="${_end##* }"
if (( $_end < $_start ))
then
# the file has been moved to a backup
_tailFile="${_file}.bak"
_end=`wc -l < "$_tailFile"`
_end="${_end##* }"
else
_tailFile="$_file"
fi
if (( $_end > $_start ))
then
_start=$(( $_start + 1 ))
sed -n "${_start},${_end}p" "$_tailFile"
fi
if [ "$_tailFile" = "$_file" ]
then
_start="$_end"
else
_start=0
fi
sleep 1
done

I didn't spend very long thinking about the above (which I tweaked from
a different script) but hopefully you get the idea - just use sed to
print out the number of lines added to the file (or it's backup if just
created) in about the past second.

Regards,

Ed.

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