bash error output

Answer

Bash provides I/O redirection. There are 3 standard files: STDIN (standard input) with descriptor 0, STDOUT (standard output) with descriptor 1 and STDERR (standard error) with descriptor 2.

If you want to redirect your messages to STDERR, you can use >&2 symbol. This symbol is abbreviation of 1>&2 symbol that means, that everything in STDOUT will goes to STDERR.

So, if you want to put message "Cannot delete directory" in STDERR, you can do it this way:

echo Cannot delete directory >&2

Even more, you might to create your own function for error messages:

recho() { echo "$*" >&2 ; }
recho "Cannot delete directory" > /dev/null

Output: Cannot delete directory

On the first line, we define recho function (error echo). This function will print all its arguments ($*) to STDERR (>&2).

On the second line, we try to use function. To prove, that output will be written to STDERR, we will redirect STDIN to nowhere (/dev/null). So, if you see some output, it should be in STDERR.