for it: one for input, one for output, and one for error messages. Typically,
these are attached to the user’s terminal (so they take input from or give
output to the command line), but they can be directed elsewhere, such as to or
from a file. These three streams are referred to and abbreviated as shown here,
and each of these is assigned a number, shown in the third column:
Stream AbbreviationNumberStandard input stdin^0Standard output stdout^1Standard error, or error streamstderr^2In the earlier section “Redirecting Output and Input,” you learned how to
redirect input and output without needing to know about stdin or stdout.
In addition, you can redirect where the stderr messages are sent and also
do some more powerful things.
If you are running a program and want any error messages that appear to be
directed into a text file instead of having them printed on a screen that might
not be monitored, you can use the following command when starting the
program or running a command (substitute program with the name of the
program or command you are running):
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matthew@seymour:~$ program 2> error.log
Here, any error messages from program are added to the end of a file named
error.log in the current working directory.
If you want to redirect both stderr and stdout to a file, use the
following:
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matthew@seymour:~$ program &> filename
You can do the same thing by using the following:
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matthew@seymour:~$ program >> filename 2>&1
In this case, any output from program is added to the end of a file named
filename.
To redirect stderr to stdout, so that error messages are printed to the