How to add timestamp to STDERR redirection

Question

In bash/ksh can we add timestamp to STDERR redirection?

E.g. myscript.sh 2> error.log

I want to get a timestamp written on the log too.

Answer 1

Here's a version that uses a while read loop like pax's, but doesn't require extra file descriptors or a separate script (although you could use one). It uses process substitution:

myscript.sh 2> >( while read line; do echo "$(date): ${line}"; done > error.log )

Using pax's predate.sh:

myscript.sh 2> >( predate.sh > error.log )