Execute command in place of the current shell (instead of creating a new process). exec is also useful for opening, closing, or copying file descriptors.
Tell command that it was invoked as name.
Remove all environment variables from the process when the new command runs.
Treat the new process as if the user were logging in.
trap 'exec 2>&-' 0Close standard error when shell script exits (signal 0) $
exec /bin/tcshReplace current shell with extended C shell $
exec < infileReassign standard input to infile