Remove substring with Ruby regular expression

Question

I would like to use Ruby's sub(pattern, replacement) for removing a line of the form last-lrm-refresh=<value> from a multi-line substring. Here is an example of the entire string:

       maintenance-mode=true \
       last-lrm-refresh=1523448810 \
       no-quorum-policy=stop

The following does not quite work:

s.sub(' \\\n[ \t]+last-lrm-refresh=[0-9]+', '')

When I try the same regular expression in an interactive regular expression editor (such as Rubular) it works fine, so I guess the problem is about escaping characters.

What is the right form of regular expression to pass a string into sub to achieve the desired effect? I've tried a few "permutations" but without success so far. (I've also tried something similar with Perl before.)

s.sub(/ \\\n[ \t]+last-lrm-refresh=[0-9]+/, '') - use a regex, not a literal string substitution. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jun 15, 2018 at 9:05
' \\\n[ \t]+last-lrm-refresh=[0-9]+' is not a regular expression. It's a string. — Tom Lord
– Tom Lord, Commented Jun 15, 2018 at 9:06

Aleksei Matiushkin · Accepted Answer · 2018-06-15 09:27:50Z

2

If you want to remove the line, it could be easier to support if you’ll be removing a line instead of regexping everything:

input = "maintenance-mode=true
       last-lrm-refresh=1523448810
       no-quorum-policy=stop"
input.split($/).reject do |line|
  line.strip.start_with?("last-lrm-refresh=")
end.join($/)
#⇒ maintenance-mode=true
#  no-quorum-policy=stop

Or, even easier for Ruby 2.4+, credits to @Stefan

input.each_line.grep_v(/(^\s*last-lrm-refresh=)/).join

edited Jun 15, 2018 at 9:27

answered Jun 15, 2018 at 9:08

Aleksei Matiushkin

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7 Comments

Stefan Over a year ago

Or something like input.each_line.grep_v(/last-lrm-refresh=/).join

rookie099 Over a year ago

Thx. The thing is that last_lrm-refresh=... may appear in the last line, in which case I'd also like to remove the previous /\\\n/. That's why the regex-based approach came to mind.

Aleksei Matiushkin Over a year ago

I am not sure I follow. My code effectively removes the whole line.

Amadan Over a year ago

@rookie099 just chomp it afterwards. The fact that the last "line" isn't a proper line should not make you jump through hoops.

Amadan Over a year ago

@Stefan: ...or easier with input.each_line.grep_v(/(^\s*last-lrm-refresh=)/).join.chomp. :)

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