Answer by Stéphane Chazelas for Is there a simple test for anything printed on stderr in shell/Bash?

You could do (POSIXly):

if { cmd 2>&1 >&3 3>&- | grep '^'>&2; } 3>&1; then  echo there was some output on stderrfi

Or to preserve the original exit status if it was non-zero:

fail_if_stderr() (  rc=$({    ("$@" 2>&1 >&3 3>&- 4>&-; echo "$?">&4) |    grep '^'>&2 3>&- 4>&-  } 4>&1)  err=$?  [ "$rc" -eq 0 ] || exit "$rc"  [ "$err" -ne 0 ] || exit 125) 3>&1

Using exit code 125 for the cases where the command returns with a 0 exit status but produced some error output.

To be used as:

fail_if_stderr cmd its args || echo "Failed with $?"