Date: Thu, 16 Feb 2006 16:45:08 -0600 From: Tim Daneliuk <tundra@tundraware.com> To: freebsd-questions@freebsd.org Subject: /bin/sh Madness Message-ID: <43F50074.8060205@tundraware.com>
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Here is a shell function that behaves quite strangely:
#!/bin/sh
#####
# Execute A Command, Noting Start/Stop Time, & Logging Output
# Args:
# $1 Command Name
# $2 Log Directory
# $3 Command String To Execute
#####
runupd()
{
log=$2/$1.log
timestamp $log
touch $2/.$1-begin && eval $3 2>&1 >> $log && touch $2/.$1-end &
}
# End of 'runupd()'
So, you might do something like:
runupd freespace /var/log/ "df -k"
Now, for the weirdness. This function works fine in my script
so long as one of two conditions is met:
1) I run it interactively from the command line (bash)
OR
2) I run it from 'cron' AND $3 is *not* another script
If I try to run it from 'cron' and point $3 to a script, everything gets
run as planned, however, the ending timestamp (touch $2/.$1-end) never
runs. That is, the initial time stamp (.$1-begin) and the command itself
are executed, and output is properly written to the logfile,
but the final timestamp never happens.
I have been fiddling with this on- and off and cannot seem to explain
the behavior. I',m guessing that something about the combination of
'cron'and the 2>&1 >> $log business is causing the last touch to never
get invoked, but for the life of me, I cannot figure this one out.
Interestingly, this works fine in Linux (SuSE 10.0). In Linux, both
'sh' and 'bash' are the same binary (bash is running as sh). So ..
I went back to FreeBSD (4.x in this case, though the problem is also
noted in 6.x) and changed the SHELL variable in the crontabs file to
use 'bash' - same problem.
This is starting to feel like a problem with file handles getting clobbered
in the FreeBSD exec logic.
Other explanations welcome...
--
----------------------------------------------------------------------------
Tim Daneliuk tundra@tundraware.com
PGP Key: http://www.tundraware.com/PGP/
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