String gsub returns an empty string, a bug?

Why does the first line return an empty string? Is this a bug or a
feature?

irb(main):001:0> a = “x”; a.gsub!(“x”,"\’")
=> “”
irb(main):002:0> a = “x”; a.gsub!(“x”,“y”)
=> “y”

On 2013-09-15, at 10:21 AM, “Sami S.” [email protected] wrote:

Why does the first line return an empty string? Is this a bug or a
feature?

irb(main):001:0> a = “x”; a.gsub!(“x”,"\’")
=> “”
irb(main):002:0> a = “x”; a.gsub!(“x”,“y”)
=> “y”


Posted via http://www.ruby-forum.com/.

There are extra backslash sequences which work in substitution strings:

[1] pry(main)> a = “wxy”; puts a.gsub!(“x”,"\’")
wyy
=> nil

Here ’ is the “remains” of the string after the match, in the Pickaxe
book it tells about the additional backslash sequences in substitution
strings:

& last match
+ last matched group
` string prior to match
’ string after match
\ literal backslash

So you need to escape the \ in ’ to stop it being interpreted as the
string after match e.g.

[2] pry(main)> a = “wxy”; puts a.gsub!(“x”,"\\’")
w’y
=> nil

Another approach might be to use a block where the returned string isn’t
using the additional backslash sequences:

[3] pry(main)> a = “wxy”; puts a.gsub!(“x”) { “\’” }
w’y
=> nil

Hope this helps,

Mike

Mike S. [email protected]
http://www.stok.ca/~mike/

The “`Stok’ disclaimers” apply.

Thank you for your answer. I’ve been reading the class reference at
(http://ruby-doc.org/core-2.0.0/String.html) which doesn’t mention the
backslash sequences…

regards,
Sami

Mike S. wrote in post #1121503:

On 2013-09-15, at 10:21 AM, “Sami S.” [email protected] wrote:

Here ’ is the “remains” of the string after the match, in the Pickaxe
book it tells about the additional backslash sequences in substitution
strings:

& last match
+ last matched group
` string prior to match
’ string after match
\ literal backslash

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