Linux exec file redirection

Linux exec file redirection exec command function exec ls execute ls in shell, after ls is completed, the original shell is not returned. exec <file uses the content in the file as the exec standard input exec> file. The content in the file is written as the standard exec 3 <file reads the file in fd3, the content read in sort <& 3 fd3 is classified as exec 4> file writes the content written into fd4 to file ls> & 4 Ls will not be displayed, the data is directly written to fd4, that is, copy fd5 exec 3 from exec 5 <& 4 created in the above file <&-Disable fd3