How do I find any space before "." - ruby

Question

I have names "example .png" and "example 2.png". I am trying to convert any space to "_" and any space before "." should be removed.
So far I am doing it like this:
file.gsub(" .",".").gsub(" ", "_").gsub(".tif", "")

Answer 1

Use an rstripped File.basename(filename,File.extname(filename)) and replace spaces with underscores inside it then add an extname:
File.basename(filename,File.extname(filename)).rstrip.gsub(" ", "_") + File.extname(filename)
See the Ruby demo
Details:
File.basename(filename,File.extname(filename)) - get file name without extension
.rstrip - remove whitespace before the extension
.gsub(" ", "_") - replaces spaces (use /\s+/ regex to remove any whitespaces) with underscores
File.extname(filename) - a file extension.
If you prefer a regex way:
s = 'some example 2 .png'
puts s.gsub(/\s+(\.[^.]+\z)|\s/) {
Regexp.last_match(1) ?
Regexp.last_match(1) :
"_"
}
(can be shortened to s.gsub(/\s+(\.[^.]+\z)|\s/) { $1 || "_" } (see Jordan's remark)).
See this Ruby demo.
Here, the pattern matches:
\s+(\.[^.]+\z) - 1 or more whitespaces (\s+) before the extension (\.[^.]+ - a dot followed with 1+ chars other than a dot before the end of string \z), while capturing the extension into Group 1
| - or
\s - any other whitespace symbol (add + after it if you need to replace whole whitespace chunks with underscores).
In the gsub block, a check is performed to test Group 1, and if it matched, only the extension is inserted into the result. Else, a whitespace is replaced with an underscore.