Backslash substitution question

ruby-talk
1

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

2

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

3

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

···

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.

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

–
Eric Hodel - drbrain@segment7.net - http://segment7.net
All messages signed with fingerprint:
FEC2 57F1 D465 EB15 5D6E 7C11 332A 551C 796C 9F04

4

Hi –

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

Are you doing this in irb? If so, you’ll get a quoted and escaped
version of the new string which shows you \ where the string actually
has \

irb(main):005:0> res = “c:/foo/bar”.gsub(///, “\”)
=> “c:\foo\bar”
irb(main):006:0> puts res
c:\foo\bar
irb(main):007:0> res.size
=> 10

David

···

On Wed, 12 Nov 2003, Ron Coutts wrote:

–
David Alan Black
home: dblack@wobblini.net # New email address
work: blackdav@shu.edu
Web: http://pirate.shu.edu/~blackdav

5

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,

···

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.

–
Ryan Pavlik rpav@mephle.com

“More hapless visitors? Tsk, and I’m all out of doom quests.” - 8BT

6

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

···

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

–
Ryan Pavlik rpav@mephle.com

“More hapless visitors? Tsk, and I’m all out of doom quests.” - 8BT

7

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

8

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