Originally Posted by Don Cragun

This discussion assumes that you are using a shell that uses basic Bourne shell redirection syntax (such as bash, ksh, or sh). The csh shell and its derivatives handle redirection differently.

The shell redirection operator 2>&1 tells the shell to redirect all ouput written to file descriptor 2 (the standard error output stream) to the file to which file descriptor 1 (the standard output stream) is directed. The order of the redirections is important. Try the following examples to see the difference.
EXAMPLE 1:

Code:

(echo abc;cp "unknown file" xyz)

This command will send the standard output from echo to your terminal and the standard error output to your terminal (unless you have performed redirections for one of these output streams that were not associated with another command).

If this isn't what happens, log out and log back in and try again to get a fresh shell execution environment with standard output and standard error output directed to your terminal.

EXAMPLE 2:

Code:

(echo abc;cp "unknown file" xyz) >fd1 2>fd2

This command will send the output from echo to the file named fd1 and the diagnostic message from cp to the file named fd2. You can verify this by running the commands:

Code:

cat fd1

and

Code:

cat fd2

EXAMPLE 3:

Code:

(echo abc;cp "unknown file" xyz) >fd1 2>&1

This command will send the output from echo to the file named fd1 and the diagnostic message from cp to the file to which file descriptor 1 is directed (which in this case is the file named fd1). Again, you can verify this by running the command:

Code:

cat fd1

EXAMPLE 4:

Code:

(echo abc;cp "unknown file" xyz) 2>&1 >fd1

This will send the diagnostic output from the cp command to the file to which file descriptor 1 is directed (your terminal) and the output from echo to the file named fd1.


If the commands:

Code:

nohup nice -10 program1a > logfile1a.txt 2>&1
nohup nice -10 program1b > logfile1b.txt 2>&1
nohup nice -10 program1c > logfile1c.txt 2>&1

send any output to logfileA.txt something is seriously wrong. This all works as I have described when tested on Mac OS X Version 10.7.5 with both bash and ksh. When I tried these using csh on OS X, it gives the diagnostic:

Code:

Ambiguous output redirect.

Of course there is one other possibility: Do program1a, program1b, and program1c internally redirect their output to logfileA.txt? If so, we have wasted a lot of time, and I assume you know how to fix your problem.