Only pipe STDERR output in bash with timestamp

bash

In order to discard standard output and only log the standard error, following command can be used. The second part of command is to prefix the current timestamp in the output

sh monitor 2>&1>/dev/null | ts '[%Y-%m-%d %H:%M:%S]'

dash

If need to run in dash, such as running in crontab, above syntax is wrong, use following command instead

sh monitor 3>&1 1>/dev/null 2>&3 3>&- | ts '[%Y-%m-%d %H:%M:%S]'

Note: This command can be run in bash too

References

Prepending a timestamp to each line of output from a command
Pipe only STDERR through a filter