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Simple Logging Function with Timestamps

Source: R/log_msg.R
log_msg.Rd

A utility function for logging messages with ISO 8601 timestamps to both the console and an optional log file. Used throughout run_MOSAIC and its helpers.

Usage

log_msg(msg, ...)

Arguments

msg

Character string. The message to log. May include sprintf-style formatting placeholders (e.g., "%d", "%s", "%.2f").

...

Additional arguments passed to sprintf for message formatting.

Value

Invisible NULL. Function is called for its side effects.

Details

Timestamps are emitted in ISO 8601 format (e.g. "2026-06-05T14:32:01-0700") so that a downstream consumer (a human tail, a monitoring AI agent, a log shipper) can parse elapsed time without ambiguity.

Lines are written to stdout and, if a log file path is known, also appended to that file. The path is resolved in this order:

  1. getOption("MOSAIC.log_file") — preferred. Set this once at the start of a pipeline (run_MOSAIC() does this automatically) and every log_msg call — including those inside helper functions whose calling frame has no dir_output variable — will write to the same file.

  2. A dir_output binding in the calling frame (legacy fallback). The file path becomes <dir_output>/run.log. This preserves backward compatibility for callers that don't set the option.

If neither source resolves a path, lines go to stdout only.

Examples

if (FALSE) { # \dontrun{
# Recommended: set the log file once at the start of a long-running
# pipeline, then every helper's log_msg() call lands in the same file.
options(MOSAIC.log_file = file.path(tempdir(), "run.log"))
on.exit(options(MOSAIC.log_file = NULL), add = TRUE)

log_msg("Starting analysis")
log_msg("Processing %d simulations with %d cores", 100, 8)
log_warn("Worker %d failed: %s", 17L, "OOM")
log_fatal("Aborting — convergence target unreachable")
} # }