Shell Programming and Scripting

a=pattern1
b=pattern2
awk -v var=$a,var1=$b '$0~var,$0~var1' file

awk -v var=$a -v var1=$b '$0~var,$0~var1' file

-------here is my code which i have written (for bottleneck look at the code RED)------
#!/bin/ksh
for SID in `cat $HOME/appleora/dblist`
do
cd $HOME/appleora/$SID/admin/bdump
cat alert_${SID}.log >>$HOME/alert_${SID}.log
cd
if [ -f alert_${SID}.log ]
then
mv alert_${SID}.log alert_out.log
touch alert_${SID}.log
YESTERDAY=`TZ=aaa24 date +"%b %d"`
TODAY=`date +"%b %d"`
echo $TODAY
echo $YESTERDAY
#awk '/Apr 15/,/Apr 16/' $HOME/alert_out.log >> $HOME/alert_work.log
#awk '/$YESTERDAY/,/$TODAY/' $HOME/alert_out.log > $HOME/alert_work.log
awk -v var=$YESTERDAY,var1=$TODAY '$0~var,$0~var1' $HOME/alert_out.log > $HOME/alert_work.log
cat alert_work.log >> alert_${SID}.hist
grep ORA- alert_work.log >> alert.err
fi
for DBA in `cat $HOME/appleora/dbalist`
do
if [ `cat alert.err|wc -l` -gt 0 ]
then
mailx -s "${SID} ORACLE ALERT ERRORS" $DBA < alert.err
else
mailx -s "${SID} ORACHECK RUN SUCCESFULLY NO ERROR" $DBA
fi
done
rm -f alert.err
rm -f alert_work.log
done
 
Now 
-----Here is my $HOME/alert_out.log file on which i am doing search and i am intreested in content between Apr 15 and Apr 16----
Wed Apr 15 09:37:05 2009
Thread 1 advanced to log sequence 46
  Current log# 3 seq# 46 mem# 0: C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\REDO03.LOG
Wed Apr 15 22:00:14 2009
Thread 1 advanced to log sequence 47
  Current log# 1 seq# 47 mem# 0: C:\ORACLE\PRODUCT\10.2.0\ORADATA\ORCL\REDO01.LOG
b_recovery_file_dest_size of 2048 MB is 0.00% used. This is a
user-specified limit on the amount of space that will be used by this
database for recovery-related files, and does not reflect the amount of
space available in the underlying filesystem or ASM diskgroup
Errors in file c:\oracle\product\10.2.0\admin\orcl\udump\orcl_ora_5388.trc:
ORA-00600: internal error code, arguments: [LibraryCacheNotEmptyOnClose], [], [], [], [], [], [], []
Thu Apr 16 09:30:56 2009

that means o/p should be in green
=====================================
Now if i use 
#awk '/Apr 15/,/Apr 16/' $HOME/alert_out.log >> $HOME/alert_work.log
then i am getting desired output as well as i am getting mail thru mailx command 
=====================================
=====================================
if i use 
#awk '/$YESTERDAY/,/$TODAY/' $HOME/alert_out.log > $HOME/alert_work.log
then this file is get created > $HOME/alert_work.log this file bt with no content 
=====================================
=====================================
and if i use 
awk -v var=$YESTERDAY,var1=$TODAY '$0~var,$0~var1' $HOME/alert_out.log > $HOME/alert_work.log
as u suggested......
i am getting below message
sh oracheck.sh
Apr 16
Apr 15
awk: syntax error near line 1
awk: bailing out near line 1
=====================================

awk -v var="$YESTERDAY" -v var1="$TODAY" '$0~var,$0~var1' $HOME/alert_out.log > $HOME/alert_work.log

Apr 16
Apr 15
oracheck.sh: Apr 15: not found
oracheck.sh: Apr 16: not found
awk: syntax error near line 1
awk: bailing out near line 1

awk -v var="$YESTERDAY" -v var1="$TODAY" '$0~var,$0~var1' $HOME/alert_out.log > $HOME/alert_work.log
awk -v var=`"$YESTERDAY"` -v var1=`"$TODAY"` '/$0~var/,/$0~var1/' $HOME/alert_out.log > $HOME/alert_work.log