Redirect the standard error to the standard output

To redirect the standard error of a shell command, just use the following syntax:

ls file-that-does-not-exist 2>&1 | grep file

Or even better not to have on the terminal the standard error just throw it in /dev/null

ls file-that-does-not-exist 2>/dev/null

The standard open or standard streams that are automatically opened are:

• 0 standard input
• 1 standard output
• 2 standard error