Linux less behavior and stderr

You have to redirect stderr to stdout:

$ ./somecommad 2>&1 | less

Check the manual for you shell (e.g. man bash.)

Maybe

command 2> command.err | less; cat command.err; rm command.err

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Addendum

Here follows a clarification for folk who neglect to carefully read the question and who didn't read the OP's clarifying comment above.

haelix pointed out:

stderr lines normally get listed inbetween stdout lines inside less

and, in a comment for early answerers, wrote:

You're telling me how to redirect stderr to stdout but that's not what I wanted. I don't want stderr to mix with stdout inside less. I would like stderr to be in the terminal when I exit less

The problem is probably platform specific, it is certainly something I have experienced on older Unix SVR4 platforms.

If, on such platforms, you do something like

 find / ... | less

any error messages (e.g. directory permissions) appear like this in less

 stdout line 1
 stdout line 2
 error message text
 stdout line 4

so that output lines are obscured by error messages.

If you refresh the page the output lines are shown correctly but you lose the error messages. When you exit less the screen is cleared except for a command prompt.

If you do something like

  find / ... 2>&1 | less

The error messages are intermingled with the standard output. Again when you exit less, the screen is empty.

If you want to first peruse only the standard output in less, then see the error messages after exiting less, you need a different solution.

That is what I was tentatively suggesting in my original, two-line answer.