#!/bin/bash
start_exec_time=$(date +%Y%m%d%H%M%S) #This is the exact time when script a.sh starts to execute.
echo "Start at:$start_exec_time"
i=0
while [ $i -lt 10 ]
do
        echo "The script a.sh is being executed"
        sleep 1
        i=$(expr $i + 1)
done
fini_exec_time=$(date +%Y%m%d%H%M%S)  #This is the exact time when script a.sh finishes  executing.
echo "Finish at:$fini_exec_time"

#!/bin/bash
echo "Start to execute the script b.sh"
echo "The script b.sh is being executed"
echo "Finish executing the script b.sh"

#!/bin/bash
i=0
while [ $i -lt 10 ]
do
        ./a >> a.log
        if tail -1 a.log | grep -q '^Finish'
        then
                cur_flag=$(tail -1 a.log | gawk -F: '{print $2}')
                if [ "x${pre_flag}" = "x${cur_flag}" ]
                then
                        echo "script b.sh is unnecessary to be executed."
                        exit
                else
                        ./b >> b.log
                fi
        fi
        pre_flag=$cur_flag
        i=$(expr $i + 1)
done
now_time=$(date +%Y%m%d%H%M%S)
echo "Finish at:$now_time" >> c.log
cp a.log a.log.$now_time
cp b.log b.log.$now_time
rm -rf a.log b.log