Backslash substitution question

[Ron Coutts]

I'm having trouble with backslashes and I don't know what is wrong. I
can't seem to write and expression that will evaluate to a string
containing a single backslash character as in "\". It seems that "\\"
in Ruby evaluates to "\\" not to "\" as I would expect. Below are a few
things I've tried. If anyone could send back a quick answer it would be
much appreciated.

res = "c:/foo/bar".gsub(/\//, "\\") # -> c:\\foo\\bar
res = "c:/foo/bar".gsub(/\//, '\\') # -> c:\\foo\\bar
#res = "c:/foo/bar".gsub(/\//, "\") # -> syntax error - unterminated
string meets end of file
#res = "c:/foo/bar".gsub(/\//, '\') # -> syntax error - unterminated
string meets end of file
res = "c:/foo/bar".gsub(/\//) { "\\"} # -> c:\\foo\\bar

Ron

[Hal Fulton]

Ron Coutts wrote:

> I'm having trouble with backslashes and I don't know what is wrong. I
> can't seem to write and expression that will evaluate to a string
> containing a single backslash character as in "\". It seems that "\\"
> in Ruby evaluates to "\\" not to "\" as I would expect. Below are a few
> things I've tried. If anyone could send back a quick answer it would be
> much appreciated.
>
> res = "c:/foo/bar".gsub(/\//, "\\") # -> c:\\foo\\bar

This one works. You're getting confused by either irb
or by calling p. You're seeing the escaped form, but it's
not stored that way internally.

Note that res.length is 10, not 12.

Hal

[Eric Hodel]

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Ron Coutts (rcoutts@envistatech.com) wrote:

> I'm having trouble with backslashes and I don't know what is wrong. I
> can't seem to write and expression that will evaluate to a string
> containing a single backslash character as in "\". It seems that "\\"
> in Ruby evaluates to "\\" not to "\" as I would expect. Below are a few
> things I've tried. If anyone could send back a quick answer it would be
> much appreciated.
>=20
> res =3D "c:/foo/bar".gsub(/\//, "\\") # -> c:\\foo\\bar
> res =3D "c:/foo/bar".gsub(/\//, '\\') # -> c:\\foo\\bar
> #res =3D "c:/foo/bar".gsub(/\//, "\") # -> syntax error - unterminated
> string meets end of file
> #res =3D "c:/foo/bar".gsub(/\//, '\') # -> syntax error - unterminated
> string meets end of file
> res =3D "c:/foo/bar".gsub(/\//) { "\\"} # -> c:\\foo\\bar

Ruby maps between / and \ in filenames on win32 just fine, why not let
it do the work for you? For cmd.exe, it doesn't cane if you give it \
or /, but tab completion doesn't work on /. (I believe I read somewhere
that the guts don't care, since back in the DOS days, but my mind could
be addled).

See also File.join and File.expand_path

--=20
Eric Hodel - [email]drbrain@segment7.net[/email] - [url]http://segment7.net[/url]
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[Ryan Pavlik]

On Wed, 12 Nov 2003 07:21:51 +0900
"Ron Coutts" <rcoutts@envistatech.com> wrote:

> I'm having trouble with backslashes and I don't know what is wrong. I
> can't seem to write and expression that will evaluate to a string
> containing a single backslash character as in "\". It seems that "\\"
> in Ruby evaluates to "\\" not to "\" as I would expect. Below are a few
> things I've tried. If anyone could send back a quick answer it would be
> much appreciated.

In any ruby string literal, backslash escapes the next character.
This is so you can write:

puts "\"hello world\"" # => "hello world"

It escapes itself, too, so you have a way of printing backslashes:

puts "\\" # => \

It works inside single quotes, so you can escape single quotes:

puts '\'' # => '

That means it needs to escape itself as well, otherwise you couldn't
print a backslash:

puts '\\' # => \

This also works inside docstrings.

hth,

--
Ryan Pavlik <rpav@mephle.com>

"*More* hapless visitors? Tsk, and I'm all out of doom quests." - 8BT

[Ryan Pavlik]

On Wed, 12 Nov 2003 07:30:08 +0900
Ryan Pavlik <rpav@mephle.com> wrote:

<basic obvious stuff>

Sorry, after seeing others post, I realize I misunderstood your
question. Yeah, what they said. Always test with puts/print. ;-)

--
Ryan Pavlik <rpav@mephle.com>

"*More* hapless visitors? Tsk, and I'm all out of doom quests." - 8BT

[Ron Coutts]

Thanks for all the help everybody and the quick turnaround, you've saved
me some valuable time. I wasn't aware of the 'quoted and escaped'
versions of these strings.

To reply to Eric, usually on win32 I just use '/' and let Ruby handle it
for me but the script I'm working on now has to enter this string into a
Windows GUI app edit field and that app doesn't like '/', that's why I
had to convert it myself.

Hal, what did you mean by 'calling p'?

Thanks again,
Ron

> -----Original Message-----
> From: Hal Fulton [mailto:hal9000@hypermetrics.com]
> Sent: November 11, 2003 3:26 PM
> To: ruby-talk ML
> Subject: Re: Backslash substitution question
>
>
> Ron Coutts wrote:

> > I'm having trouble with backslashes and I don't know what

> is wrong. I

> > can't seem to write and expression that will evaluate to a string
> > containing a single backslash character as in "\". It

> seems that "\\"

> > in Ruby evaluates to "\\" not to "\" as I would expect.

> Below are a few

> > things I've tried. If anyone could send back a quick

> answer it would be

> > much appreciated.
> >
> > res = "c:/foo/bar".gsub(/\//, "\\") # -> c:\\foo\\bar

>
> This one works. You're getting confused by either irb
> or by calling p. You're seeing the escaped form, but it's
> not stored that way internally.
>
> Note that res.length is 10, not 12.
>
> Hal
>
>

[Hal Fulton]

Ron Coutts wrote:

> Hal, what did you mean by 'calling p'?

The p method is similar to puts or print, but it invokes
the 'inspect' method on the object, so it's displayed
in a specialized (or user-defined) way.

p "\\" # "\\"
puts "\\" # \

Useful for debugging, especially if you create "pretty"
inspect methods.

Hal