The input command causes the tracer to read its next command from the specified destination. Once the tracer reaches the end of an input file, it looks to standard input for commands. However, specifying a "+" in the command causes the tracer to resume taking commands from the destination file after it reaches the end-of-file.
input [+] <destination>
destination
Specifies the destination, either standard input (for example, cin) or a file name.
Only standard input or the name of the current file can appear without the plus sign (+).