Understanding Shell Scripting

Shell Programming and Scripting
1

Hi Gurus,

Im new to Shell scripting. I have a shell script which basically sends an email when called thorugh my ETL tool. Wanted to understand the its functionality in detail. Would be great it any one can explain what exactly the commands to

#!/bin/sh
 
# Dummy UUCP rmail command for postfix/qmail systems
 
SENDMAIL="/usr/sbin/sendmail"
IFS=" " read junk from junk junk junk junk junk junk junk relay
 
case "$from" in
*[@!]*) ;;
      *) from="$from@$relay";;
esac
 
exec $SENDMAIL -i -f "$from" -- "$@"
2 
#!/bin/sh ---> script header

# Dummy UUCP rmail command for postfix/qmail systems -->comments

SENDMAIL="/usr/sbin/sendmail" -->variable declared and sets a command path
IFS=" " read junk from junk junk junk junk junk junk junk relay

case "$from" in -->case check
*[@!]*) ;; -----> it is checking any @ or ! available in the input
      *) from="$from@$relay";;
esac

exec $SENDMAIL -i -f "$from" -- "$@" --> send mail