Log::Progress implements a text protocol for progress reporting through a standard text logfile. Progress bars are a nice feature to have, but often take more time to implment than the project is worth. This approach allows you to add simple text output to a script or module and then view it from the command line or write web views to display it.
The syntax for progress-update messages is:
"progress:" WS [STEP_ID WS] FRACTION [WS "-"] [WS MESSAGE]
the syntax for declaring a new sub-step is:
"progress:" WS STEP_ID WS ["(" CONTRIBUTION ")" | "-"] WS TITLE
and the syntax for arbitrary progress-related data is:
"progress:" WS [STEP_ID WS] "{" JSON "}"
where WS is one or more whitespace characters, the optional STEP_ID designates a sub-step, FRACTION is either a floating point number between 0 and 1 or a fraction (whose numerator and denominator could be floating point numbers), CONTRIBUTION is a floating point number between 0 and 1 indicating how step progress affects the parent progress, MESSAGE and TITLE are plain text, and JSON is arbitrary JSON content to be used for special cases or extensions.
This sequence gives you a basic progress bar:
progress: 0
progress: 0.3
progress: 0.7
progress: 0.9
progress: 1
This gives you status labels for the progress bar:
progress: 0.00 - Preparing to do the thing
progress: 0.75 - The thing is mostly done
progress: 0.90 - Cleaning up loose ends
progress: 1.00 - Done
If you want to divide the progress into multiple sub-steps:
progress: collect (.2) Building catalog of things to sync
progress: check (.2) Checking catalog vs. remote catalog
progress: xfer (.5) Transferring data
progress: commit (.1) Committing transaction
progress: collect 400/4000
progress: collect 800/4000
progress: collect 1600/8000
progress: collect 9000/10000
progress: collect 10000/10000
progress: check 0.1 - 1000 of 10000
progress: check 0.7 - 7000 of 10000
progress: check 1
progress: xfer 0.5 - 228 of 456
progress: xfer 1
progress: commit 1 - All changes saved
In that example, the sub-steps were performed in sequence, but you can see how it is possible to have steps overlap, which could be rendered as multiple progress bars moving in parallel. You can also see an example of the sub-step percentages, where the full progress of a sub-step represents some portion of the parent progress bar. If those are omitted, you can continue to report overall progress independent of the sub-steps.
Sub-steps can have their own sub-steps:
progress: copy - Copy files
progress: copy.f1 (.001) File One
progress: copy.f1.data (.9) File One data xfer
progress: copy.f1.cksm (.1) File One verify checksum
but that level of detail could also just be shown in the progres status message. But options are nice.