Trying to understand a crontab job for my database export and reloading

Question

FILE=ENTP_`date "+%d%m%y"`.dmp.Z
LOG=ENTP_`date "+%d%m%y"`.log
rm -f /tmp/exp_pipe
*/sbin/mknod /tmp/exp_pipe p*compress < /tmp/exp_pipe > $FILE | echo $PASS | exp ben@XEPROD tables=TBL_ABCD,TBL_EFGH,TBL_IJKLM_QWER triggers=n direct=y *file=/tmp/exp_pipe* log=$LOG
rm -f /tmp/exp_pipei don't understand the bold parts.
what i know from /sbin is, anything that is put within there is for root command only. So my thinking, the above job can only executed in root enviroment.
the file part , what i understand is oracle exp / imp command and normally the file= will be like file=some.dmp . So now it become /tmp/exp_pipe which causes much confusion. Cos according to the declare variable, it should be file=$FILE .

Answer 1

flaskvacuum wrote:
FILE=ENTP_`date "+%d%m%y"`.dmp.Z
LOG=ENTP_`date "+%d%m%y"`.log
rm -f /tmp/exp_pipe
*/sbin/mknod /tmp/exp_pipe p*compress < /tmp/exp_pipe > $FILE | echo $PASS | exp ben@XEPROD tables=TBL_ABCD,TBL_EFGH,TBL_IJKLM_QWER triggers=n direct=y *file=/tmp/exp_pipe* log=$LOG
rm -f /tmp/exp_pipei don't understand the bold parts. The parts you've marked are simply formatting options for the date command:
# date
Tue Feb  7 17:26:49 PST 2012
# date '+%d'
07
# date '+%m'
02
# date '+%y'
12
# date '+%d%m%y'
070212
#The date command, along with its formatting options, is wrapped in backticks. This will fork a shell to run the subcommand, and substitute the shell's output (the output of the date command) into the containing string. That containing string is defining a variable. Taking the first example:
# echo $FILE
# FILE=ENTP_`date "+%d%m%y"`.dmp.Z
# echo $FILE
ENTP_070212.dmp.Z
#>
what i know from /sbin is, anything that is put within there is for root command only. So my thinking, the above job can only executed in root enviroment. There are a number of utilities in /sbin that can be run as normal users, perhaps with a more restricted impact. That subdirectory just contains things that a normal user doesn't regularly need to have on their search path ($PATH).
the file part , what i understand is oracle exp / imp command and normally the file= will be like file=some.dmp . So now it become /tmp/exp_pipe which causes much confusion. Cos according to the declare variable, it should be file=$FILE.The named pipe being used in your example is to compress the output, thereby reducing disk space. Breaking the example down into a more simplistic example:
bryan$ FILE=ENTP_`date "+%d%m%y"`.test.out.Z
bryan$ echo $FILE
ENTP_070212.test.out.Z
bryan$ rm -f /tmp/exp_pipe
bryan$ mknod /tmp/exp_pipe p
bryan$ compress < /tmp/exp_pipe > $FILE | echo this is a simple test > /tmp/exp_pipe
bryan$ ls -la $FILE
-rw-rw-r--. 1 bryan bryan 27 Feb  7 17:46 ENTP_070212.test.out.Z
bryan$ file ENTP_070212.test.out.Z
ENTP_070212.test.out.Z: compress'd data 16 bits
bryan$ zcat ENTP_070212.test.out.Z |more
this is a simple test
bryan$The mknod creates the pipe, compress reads FROM the pipe, and writes the compressed output TO $FILE. You could have put compress in the background with an ampersand, but simply suffixing it with a pipe has the same effect given that when "exp" is finished writing to the pipe (signaled by EOF), compress would return anyway. The end result is something like this:
exp command file=pipe_file --> compress reading FROM the pipe_file --> $FILE which is a *.Z file indicating it is compressed output.
Best Regards,
Bryan Wood