Shell Programming and Scripting

#!/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" -- "$@"

#!/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