19 2 * * *  > /path/to/lockfile && echo 'startSA' > /path/to/lockfile
20 2 * * *  /path/to/SA >   /path/to/logfile
21 2 * * *  /path/to/SB >> /path/to/logfile
22 2 * * *  /path/to/SC >> /path/to/logfile

export start_parm='startSA'
while true
do
   grep -q "$start_parm" /path/to/lockfile
   [ $?  -eq 0 ]  && break
   sleep 1
done
# script code goes here
# ....
# ....
#
# last line of code:
echo 'startSB' > /path/to/lockfile
exit

export start_parm='startSB'
while true
do
   grep -q "$start_parm" /path/to/lockfile
   [ $?  -eq 0 ]  && break
   sleep 1
done
# script code goes here
# ....
# ....
#
# last line of code:
echo 'startSC' > /path/to/lockfile
exit

export start_parm='startSC'
while true
do
   grep -q "$start_parm" /path/to/lockfile
   [ $?  -eq 0 ]  && break
   sleep 1
done
# script code goes here
# ....
# ....
#
# last line of code:
echo 'endALL' > /path/to/lockfile
exit