# Escaped characters from the command-line

**URL:** <https://www.ruby-forum.com/t/escaped-characters-from-the-command-line/136739>\
**Category:** Ruby\
**Created:** [May 6, 2008, 12:46am UTC](https://www.ruby-forum.com/t/escaped-characters-from-the-command-line/136739 "2008-05-06T00:46:25Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![S-jb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/43a26b/32.png) [@S-jb](https://www.ruby-forum.com/u/S-jb)\
**Post date:** [May 6, 2008, 12:46am UTC](https://www.ruby-forum.com/t/escaped-characters-from-the-command-line/136739/1 "2008-05-06T00:46:25Z")

</div>

I’ve run into a bit of an issue that I hope you can help with.  
I am working on a parser that allows the user to provide a delimiter as  
an argument to the script. However, I can not find a way to [elegantly]  
handle escaped characters (such as \t and \n).  
A simplified example to illustrate:

# Using

s = ARGV.shift  
puts [‘west’, ‘side’, story’].join(s)

$ ./parse.rb ‘\t’  
=\> west\tside\tstory

Now, I can do something like:

s = ARGV.shift  
sep = s =~ /^\(.)/  
when ‘t’  
“\t”  
when ‘n’  
“\n”

# …

else  
s  
end  
end

$ ./parse.rb ‘\t’  
=\> west side story

But I feel that is probably too brittle. I tried Shellwords, but that  
didnt seem to help (although I could have been using it incorrectly).  
Any suggestions are welcome.  
Thanks.

---

<div class="post-metadata">

**Author:** ![S-jb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/43a26b/32.png) [@S-jb](https://www.ruby-forum.com/u/S-jb)\
**Post date:** [May 6, 2008, 5:17pm UTC](https://www.ruby-forum.com/t/escaped-characters-from-the-command-line/136739/2 "2008-05-06T17:17:22Z")

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-j b- wrote:

> I am working on a parser that allows the user to provide a delimiter as  
> an argument to the script. However, I can not find a way to [elegantly]  
> handle escaped characters (such as \t and \n).  
> A simplified example to illustrate:
> 
> # Using
> 
> s = ARGV.shift  
> puts [‘west’, ‘side’, story’].join(s)
> 
> $ ./parse.rb ‘\t’  
> =\> west\tside\tstory

It isn’t a Ruby issue. It’s a shell one. You need to find out how it’s  
possible, in your shell, to specify those special characters. Are you  
using Linux? Bash?

$ echo one\ntwo  
onentwo

$echo ‘one\ntwo’  
one\ntwo

$echo $‘one\ntwo’  
one  
two

$echo ‘one  
two’  
onw  
two

$echo “one  
two”  
onw  
two

So there are at least three ways to do \n in bash.

---

<div class="post-metadata">

**Author:** ![S-jb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/43a26b/32.png) [@S-jb](https://www.ruby-forum.com/u/S-jb)\
**Post date:** [May 6, 2008, 9:53pm UTC](https://www.ruby-forum.com/t/escaped-characters-from-the-command-line/136739/3 "2008-05-06T21:53:45Z")

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> I’m still looking for a more elegant way then the  
> heavy case statement.  
> I’ve experimented with a gsub! solution but the way backslashes are  
> escaped in regular expressions (particularly when reinserting into a  
> string) has me blocked at the moment.

All you’re looking for is a cool one-liner? Here’s one:

s.gsub!(/(\[ntr])/) { eval %/"#$1"/ }

It replaces any \n and \t sequence by it’s character. You can even  
enhance the regexp to support \x sequences as well:

s.gsub!(/(\([ntr]|x\d+))/) { eval %/"#$1"/ }

---

<div class="post-metadata">

**Author:** ![S-jb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/43a26b/32.png) [@S-jb](https://www.ruby-forum.com/u/S-jb)\
**Post date:** [May 6, 2008, 6:27pm UTC](https://www.ruby-forum.com/t/escaped-characters-from-the-command-line/136739/4 "2008-05-06T18:27:10Z")

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Albert S. wrote:

> -j b- wrote:
> 
> > I am working on a parser that allows the user to provide a delimiter as  
> > an argument to the script. However, I can not find a way to [elegantly]  
> > handle escaped characters (such as \t and \n).  
> > A simplified example to illustrate:
> > 
> > # Using
> > 
> > s = ARGV.shift  
> > puts [‘west’, ‘side’, story’].join(s)
> > 
> > $ ./parse.rb ‘\t’  
> > =\> west\tside\tstory
> 
> It isn’t a Ruby issue. It’s a shell one. You need to find out how it’s  
> possible, in your shell, to specify those special characters. Are you  
> using Linux? Bash?

Yes. Yes. But the idea is that it shouldnt matter.

> So there are at least three ways to do \n in bash.

I know that it possible, from a user standpoint, to input a special  
character in multiple ways. My concern is that I dont want to force that  
restriction on the user. For example, the utility tr will accept ‘\t’ as  
a single character; I find this ultimately more useful than tr ‘^v[tab]’  
’ ’ (or any of the above mentioned methods).  
If it is a shell issue then I am forced to modify the arguments  
accordingly. However, I’m still looking for a more elegant way then the  
heavy case statement.  
I’ve experimented with a gsub! solution but the way backslashes are  
escaped in regular expressions (particularly when reinserting into a  
string) has me blocked at the moment.

Thanks.

j

---

<div class="post-metadata">

**Author:** ![S-jb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/43a26b/32.png) [@S-jb](https://www.ruby-forum.com/u/S-jb)\
**Post date:** [May 6, 2008, 10:04pm UTC](https://www.ruby-forum.com/t/escaped-characters-from-the-command-line/136739/5 "2008-05-06T22:04:34Z")

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- -j b- wrote:

|\> It isn’t a Ruby issue. It’s a shell one. You need to find out how it’s  
|\> possible, in your shell, to specify those special characters. Are you  
|\> using Linux? Bash?  
|  
| Yes. Yes. But the idea is that it shouldnt matter.

Have fun rewriting the \*NIX shells, cmd.exe, and, possibly, PowerShell,  
too.

* * *

Phillip G.  
Twitter: [twitter.com/cynicalryan](http://twitter.com/cynicalryan)  
Blog: [http://justarubyist.blogspot.com](http://justarubyist.blogspot.com)

Use statement labels that mean something.  
~ - The Elements of Programming Style (Kernighan & Plaugher)  
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