In-place progress output to the console: How to empty the current line

Question

I have a Ruby script that outputs progress messages on the same line, using the carriage return character, like this:

print "\r#{file_name} processed."

As an example, the output changes from 'file001.html' processed. to 'file002.html.' processed and so on until the script completes.

I'd like to replace the last progress message with Done., but I can't just write print "\rDone." because that piece of code outputs something like this:

Done.99.html processed.

I guess I have to empty the line after the last progress message and then print Done.. How do I do that?

@SergioTulentsev because some terminals actually do line-wrapping. — Reactormonk
– Reactormonk, Commented Dec 2, 2012 at 20:11

qqx · Accepted Answer · 2012-12-02 20:07:43Z

7

You need to send the sequence of bytes that corresponds to the terminfo variable clr_eol (capability name el) after using \r. There are several ways that you could get that.

Simplest, assume that there's a constant value. On the terminals I've checked it is \e[K, but I've only checked a couple. On both of those the following works:

clear = "\e[K"
print "foo 123"
print "\r#{clear}bar\n"

You could also get the value using:

clear = `tput el`

Or you could use the terminfo gem:

require 'terminfo'
clear = TermInfo.control_string 'el'

answered Dec 2, 2012 at 20:07

qqx

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2 Comments

Miscreant Over a year ago

clear = `tput el` doesn't work where the tput command is not available (e.g. Windows).

qqx Over a year ago

Obviously it wouldn't. Not being able to completely rely on that being available is part of the reason I gave other alternatives.

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