File Descriptor String Syntax

You can direct one file descriptor's output to the same location as that specified by another file descriptor by using the syntax

fdattr=@other_fd

For example,

2w=@1

means that the standard error is to be sent wherever the standard output is going. You cannot do this for a file descriptor string that uses the p attribute.

If the behavior of the second file descriptor in this syntax is changed later in the -I argument list, the change does not affect the earlier reference to the file descriptor. That is, the -I argument list is parsed from left to right.

You can tie a file descriptor's output to a file by using the syntax

fdattr=filename

For example,

10w=output

says that the stream associated with file descriptor 10 is to be written to the file output. Once again, however, you cannot use this feature for a file descriptor defined with the p attribute.

In the following example, the standard input is read from the pty, the standard output is written to the pty, and the standard error is sent to the file named errors:

% mprun -I "0rp,1wp,2w=errors" a.out

If you use the w attribute without specifying a file, the file descriptor's output is written to the corresponding output stream of the parent process; the parent process is typically a shell, so the output is typically written to the user's terminal.

For multiprocess jobs, each process creates its own file; the file is opened on the node on which the process runs.

If output is redirected such that multiple processes open the same file over NFS, the processes will overwrite each other's output.

In specifying the individual file names for processes, you can use the following symbols:

• &J - The job ID of the job

• &R - The rank of the process within the job

The symbols will be replaced by the actual values. For example, assuming the job ID is 15, this file descriptor string

1w=myfile.&J.&R

redirects standout output from a multiprocess job to a series of files named myfile.15.0, myfile.15.1, myfile.15.2, and so on, one file for each rank of the job.

In the following example, there is no standard input (it comes from /dev/null), and the standard output and standard error are written to the files out.job.rank:

% mprun -I "0r=/dev/null,1w=out.&J.&R,2w=@1" a.out

This is the behavior of the -B option. See "Introducing mprun I/O ". Note the inclusion in this example of a file descriptor string for standard input even though the job has none. This is required because both standard output and standard error are redirected.