Issue #12694 has been updated by znz (Kazuhiro NISHIYAMA).


> `str.sub(/^#{Regexp.escape(substr)}/, '') #=> 'def'`

I think `^` should be `\A` in description of this ticket. (and maybe in handle_tag_name_mixin.rb of fluentd too)

Which is expected?: first prefix of string only or prefix of each line

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Feature #12694: Want a String method to remove heading substr
https://bugs.ruby-lang.org/issues/12694#change-65195

* Author: sonots (Naotoshi Seo)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
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I often write codes like:

```ruby
str = 'abcdef'
substr = 'abc'
str[substr.size..-1] if str.start_with?(substr) #=> 'def'
# or
str.sub(/^#{Regexp.escape(substr)}/, '') #=> 'def'
```

I want a short hand which is something like:

```ruby
str = 'abcdef'
substr = 'abc'
str.lstrip(substr) #=> 'def'
```

Having similar argument for `String#rstrip` would be nice for symmetry although we already have `String#chomp(substr)`

My frequent use-case is coming from fluentd. We have `remove_tag_prefix` option to remove a heading substring from a tag. We currently using `String#sub` with a regular expression, but I feel regular expression matching is too much just to remove a heading substring. https://github.com/fluent/fluentd/blob/75005f18d48ed3d416890413fa5f83982b264c71/lib/fluent/compat/handle_tag_name_mixin.rb#L45



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