# Ruby RE expression anomaly

**URL:** <https://www.ruby-forum.com/t/ruby-re-expression-anomaly/160816>\
**Category:** Ruby\
**Created:** [February 20, 2009, 12:00am UTC](https://www.ruby-forum.com/t/ruby-re-expression-anomaly/160816 "2009-02-20T00:00:45Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [February 20, 2009, 12:00am UTC](https://www.ruby-forum.com/t/ruby-re-expression-anomaly/160816/1 "2009-02-20T00:00:45Z")

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Hi,

I’m trying to use Ruby REs to transform Windows addresses into HTML  
anchors.

CODE:  
DEBUG = 1  
fo= File.open(“Microsoft EXEs xformed.txt”, “w”)  
fi= File.new(“Microsoft EXEs.txt”)  
fi.each { |line|  
next unless line =~ /11/  
p "1: " + line if DEBUG  
line.sub!( /^(.\*\)(\w+.\w+)$/i, ’

\2

')  
p “2: " + line if DEBUG  
line.sub!(/(HREF=”)/, ‘\1file:\\\’)  
p "3: " + line if DEBUG  
fo.write(line)  
}  
fi.close  
fo.close

OUTPUT (in Sci/TE:)  
“1: F:\Program Files\Microsoft Office\Visio11\VISIO.EXE\n”  
"2: \<a HREF="F:\Program Files\Microsoft Office\Visio11\VISIO.EXE  
“\> VISIO.EXE   
\n”  
“3: \<a HREF=“file:\\F:\Program Files\Microsoft Office\Visio11  
\VISIO.EXE”\> VISIO.EXE   
\n”  
[snip]

Note that output displayed within Sci/TE has all backslashes and  
quotes escaped with prefixed backslashes.

QUESTION 1:  
Displayed line 3 appears to have only two escaped backslashes at the  
start of the HREF address.  
However my 2nd substitution supplies three escaped backslashes.  
Furthermore, the 1st line of the output file confirms that only two  
backslashes were inserted.  
Can you see any reason for not getting all three backslashes specified  
in the RE?

QUESTION 2:  
This question may be inappropriate for this newsgroup, so please  
ignore it unless you care to answer it.  
Happily, the two slashes generated above were sufficient for Firefox  
3 running over WinXP-Pro/SP3 to recognize that the HREF referred to a  
local file. (I thought I need three slashes for that.)

However, Firefox (I guess) blocked the execution of it and offered  
only to save it. I’m running under Admin privileges on my own home  
machine. Is there anyway for me to the Windows program launched?

Thanks in Advance,  
Richard

---

<div class="post-metadata">

**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [February 20, 2009, 1:28am UTC](https://www.ruby-forum.com/t/ruby-re-expression-anomaly/160816/2 "2009-02-20T01:28:11Z")

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RichardOnRails wrote:

> 

1. My tests show that you need 10 backslashes in the substitution to get  
3 in the final result.

line = “HREF=”  
line.sub!(/(HREF=)/, ‘\1file:\\\\\’)

p line  
puts line

–output:–  
“HREF=file:\\\”  
HREF=file:\\

10 backslashes in sub  
----------------------- = 3.3 backslashes per desired backslash. lol.  
3 backslashes in final result

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**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [February 20, 2009, 4:20pm UTC](https://www.ruby-forum.com/t/ruby-re-expression-anomaly/160816/3 "2009-02-20T16:20:01Z")

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2009/2/19 RichardOnRails [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> I’m trying to use Ruby REs to transform Windows addresses into HTML  
> anchors.
> 
> CODE:  
> DEBUG = 1  
> fo= File.open(“Microsoft EXEs xformed.txt”, “w”)  
> fi= File.new(“Microsoft EXEs.txt”)  
> fi.each { |line|  
> …  
> }  
> fi.close  
> fo.close

I suggest rewriting this as

File.open “Microsoft EXEs.txt” do |fi|  
File.open “Microsoft EXEs xformed.txt”, “w” do |fo|  
fi.each …  
end  
end

First, the block form of File.open is much safer because then file  
handles will _always_ be closed which is not the case for your  
version.

Second, do the less dangerous operation first, because if that fails  
you do not accidentally overwrite file “Microsoft EXEs xformed.txt”.

Cheers

robert

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**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [February 20, 2009, 4:02am UTC](https://www.ruby-forum.com/t/ruby-re-expression-anomaly/160816/4 "2009-02-20T04:02:33Z")

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From: 7stud – [[mailto:removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)]

# backslash. lol.

# 3 backslashes in final result

you can do,

line.sub!(/(HREF=)/){|x| x+‘file:\\\’}

well, if you work on strings and on OSes that use backslashes as  
file/dir separators, it will be fun-ny 🙂

kind regards -botp  
(replying in gmail; apologies in advance if this gets duplicated, my  
outlook program is acting weird 🙂

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**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [February 24, 2009, 8:05am UTC](https://www.ruby-forum.com/t/ruby-re-expression-anomaly/160816/5 "2009-02-24T08:05:36Z")

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- RichardOnRails (2009-02-19) schrieb:

> OUTPUT (in Sci/TE:)  
> “1: F:\Program Files\Microsoft Office\Visio11\VISIO.EXE\n”  
> "2: \<a HREF="F:\Program Files\Microsoft Office\Visio11\VISIO.EXE  
> “\> VISIO.EXE   
> \n”  
> “3: \<a HREF=“file:\\F:\Program Files\Microsoft Office\Visio11  
> \VISIO.EXE”\> VISIO.EXE   
> \n”  
> [snip]

Replace these backslashes with slashes. Even Windows accepts this and  
it’s legal URI syntax.

mfg, simon … l

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<div class="post-metadata">

**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [February 21, 2009, 8:52pm UTC](https://www.ruby-forum.com/t/ruby-re-expression-anomaly/160816/6 "2009-02-21T20:52:03Z")

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On Feb 19, 10:00 pm, botp [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> kind regards -botp  
> (replying in gmail; apologies in advance if this gets duplicated, my  
> outlook program is acting weird 🙂

Hi botp,

Thanks for your response. It somehow gets around the problem with my  
approach, which seems to perform string-substitution twice, as I  
mentioned to the previous respondent.

Just for the record, I had to sub the string HREF=" to get the result  
I was after.

> well, if you work on strings and on OSes that use backslashes as  
> file/dir separators, it will be fun-ny 🙂

I am working on WinXP, which as you no doubt know uses backslashes for  
separators. Thanks to the previous respondent’s use of puts in place  
of p, the debugging output looks much neater. And sticking file:\  
in front of a name of a file-system object gets Windows to handle the  
local file through the browser. The only problem for my purposes is  
(apparently) that the browser won’t invoke the local file; it only  
permits saving a copy of it somewhere else in the file-system.

Again, thanks for your very neat expression.

Best wishes,  
Richard