Oracle and BASH : How to calculate how many minutes have elapsed between two timestamps

There are many ways to calculate minutes passed between two timestamps. The script below is to calculate how many minutes passed between two time stamps using oracle database.

Script : test.sh
====================
#!/bin/bash

# Create a function to accept two timestamps. The order of the timestapms (FROM_TIME, TO_TIME) does not affect the result.
fn_howmany_mins()
{
FROM_TIME=$1
TO_TIME=$2
MINS=`sqlplus -S "/ as sysdba " <<EOF
set echo off
set feedback off
set linesize 10;
set pagesize 0
set trimspool on
set space 0
set truncate on
select abs(round((to_date('$TO_TIME','YYYYMMDD_HH24MISS')-to_date('$FROM_TIME','YYYYMMDD_HH24MISS'))*1440)) from dual;
exit;
EOF`
MINS=`echo $MINS`
echo $MINS
}

#SET up test time stapms as below.
FROM_TIME=20150811_110601
TO_TIME=`date +"%Y%m%d_%H%M%S"`
echo "FROM_TIME=$FROM_TIME TO_TIME=$TO_TIME"

#Call the function to calculate the minutes.
fn_howmany_mins $FROM_TIME $TO_TIME

Sample output sh ./test.sh

==================

FROM_TIME=20150811_111458 TO_TIME=20150811_110601

9

In an actual usage remove the echo statement to get pure number . e.g. number 9 above

Bash : How to get last character in a string

Last character in a string can be extracted using sed. example:-

$cat test.sh

#!/bin/bash

STRING="Humpty Dumpty"

STRING=`echo "$STRING"|sed -e 's/\(^.*\)\(.$\)/\2/'`

echo "STRING=$STRING"

exit 0

Output:-

STRING=y

How to send select rows into a while loop (bash)

Sample File:-  test.txt

2015-08-01  WHY=Beacuse of testing

DATE=2015-08-01  Beacuse of testing

DATE=2015-08-01  WHY=Beacuse of testing

2015-08-01  Beacuse of testing

Sample script:script.sh

head -3 test.txt|while read LINE

do

echo  "LINE=$LINE"

STR1=`echo $LINE|awk '{print $1}'`

STR2=`echo $LINE|awk '{first=$1; $1=""; print $0}'`

VALU1=`echo $STR1|awk -F\= '{print $2}'`

VALU1="${VALU1:-$STR1}"

LABL1=`echo $STR1|awk -F\= '{print $1}'` 

if [ "$VALU1" == "$STR1" ]

   then

   LABL1=''

   export STR1

fi

VALU2=`echo $STR2|awk -F\= '{first=$1; $1="";print $0}'`

VALU2="${VALU2:-$STR2}"

LABL2=`echo $STR2|awk -F\= '{print $1}'`

if [ "$VALU2" == "$STR2" ]

   then

   LABL2=''

   export STR1

fi

echo "STR1=$STR1 "

echo "LABL1=$LABL1"

echo "VALU1=$VALU1"

echo -e "\t\tSTR2=$STR2 "

echo -e "\t\tLABL2=$LABL2"

echo -e "\t\tVALU2=$VALU2"

echo -e "\n\n"

done

Sample Output:-

LINE=2015-08-01  WHY=Beacuse of testing

STR1=2015-08-01 

LABL1=

VALU1=2015-08-01

STR2= WHY=Beacuse of testing 

LABL2=WHY

VALU2= Beacuse of testing

LINE=DATE=2015-08-01  Beacuse of testing

STR1=DATE=2015-08-01 

LABL1=DATE

VALU1=2015-08-01

STR2= Beacuse of testing 

LABL2=

VALU2= Beacuse of testing

LINE=DATE=2015-08-01  WHY=Beacuse of testing

STR1=DATE=2015-08-01 

LABL1=DATE

VALU1=2015-08-01

STR2= WHY=Beacuse of testing 

LABL2=WHY

VALU2= Beacuse of testing