Redirect output to a file in Linux

To redirect stdout to file.txt:

echo test > file.txt

This is equivalent to:

echo test 1> file.txt

To redirect stderr to file.txt:

echo test 2> file.txt

To combine stdout and stderr

echo test > file.txt 2>&1

Here in 2>&1:

• 2> redirects stderr to an (unspecified) file.
• &1 redirects stderr to stdout.

So >& is the syntax to redirect a stream to another file descriptor:

• 0 is stdin
• 1 is stdout
• 2 is stderr

Thus, To redirect stdout to stderr:

echo test 1>&2   # equivalently, echo test >&2

Order matters

echo test 2>&1 >>file != echo test >>file 2>&1

cmd 2>&1 >>file does not redirect stderr to the file,
but cmd >> file 2>&1 does.

In the first case, stderr is redirected to the stdout of the shell and then stdout is directed to the file.

In the second case, stdout is directed to the file, and then stderr is directed to the same place.

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Resources:

• StackOverflow