gnd

The log operation writes a message at a specified log level and then returns the last value unchanged. It accepts an optional destination, an optional level, and zero or more message parts. If you specify a level, you must also provide a destination to bind the final value; if you omit both, logging and binding default to the current _ value at the info level.

The syntax of the log operation is:

[ $destination ] log [ level [ value1 [ value2 … ] ] ]

If no arguments are given, log is equivalent to logging _ at info and rebinding it to _. If only a level is provided, you must supply a $destination, for example:

_ log debug

logs the current _ at DEBUG and leaves it unchanged. To log a custom message, specify destination, level, and values:

$msg log warn “Low disk space:” $availableSpace

If availableSpace holds 1024, this writes

Low disk space: 1024

to stderr at WARN level and binds 1024 to msg. Any misuse—such as specifying a level without a destination—results in a parse or runtime error. All identifiers follow single‑assignment rules.