Learning Linux Shell Scripting - Second Edition

Summarizing usage of the exec command

The following is a summary of the exec command for using various file handling-related operations:

Command	What it does
exec command	This command will replace shell and execute it. Therefore, it will not return to its original shell, which started it.
exec > data.txt	This opens data.txt for writing standard output.
exec < data.txt	This opens data.txt for reading standard input.
exec 3< data.txt	This opens data.txt for reading with descriptor 3.
sort <&3	This will sort the data.txt file.
exec 4> data.txt	This opens data.txt for writing with descriptor 4.
ll >&4	The output of ll is redirected to data.txt.
exec 6<&5	This makes fd 6 a copy of fd 5.