Using Preconnected Standard I/O Files

If you do not use an OPEN statement to open logical unit 5, 6, or 0 and do not set the appropriate environment variable (FORTn), Intel Fortran,at run time, implicitly opens (preconnected) units 5, 6, and 0 and associates them with the following operating system standard I/O files:

Unit	Environment Variable	Equivalent Linux* Standard I/O File
5	FORT5	Standard input, stdin
6	FORT6	Standard output, stdout
0	FORT0	Standard error, stderr

You can change these preconnected files by doing one of the following:

Using an OPEN statement to open unit 5, 6, or 0. When you explicitly OPEN a file for unit 5, 6, or 0, the OPEN statement keywords specify the file-related information to be used instead of the preconnected standard I/O file.
Setting the appropriate environment variable (FORTn) to redirect I/O to an external file.

To redirect input or output from the standard preconnected files at run time, you can set the appropriate environment variable or use the appropriate shell redirection character in a pipe (such as > or <).