set(4) log_rewrite

If this /SET is defined (by default, it is un-set), then every time a LOGICAL line of output is about to be sent to a window, the /SET value is expanded, and the result of that expansion is substituted for the original text. The expansion is parsed in the context that: $0 The window refnum the output is going to $1- The text itself.

This would cause all output to all windows to be preceded in the logfile by +++

/SET LOG_REWRITE +++$1-

This would return proceed all output to all logfiles with the output of the user defined function $myfunc() called with the window number.

/SET LOG_REWRITE $myfunc($0) $1-

When changing /set output_rewrite inside of an alias, please remember that $'s are expanded before the /set is called, and so things like $1- or $myfunc($0) would be expanded at the /set time and not at the rewrite time. Make sure to double up your $$'s in such cases!

This provides an effective way to alter data as it is written to logfiles.