# HOWTO Use Veriables inside of Regexp and Commands?

**URL:** <https://www.ruby-forum.com/t/howto-use-veriables-inside-of-regexp-and-commands/56959>\
**Category:** Ruby\
**Created:** [April 6, 2006, 2:11am UTC](https://www.ruby-forum.com/t/howto-use-veriables-inside-of-regexp-and-commands/56959 "2006-04-06T02:11:11Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![pyr0](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/da6949/32.png) [@pyr0](https://www.ruby-forum.com/u/pyr0)\
**Post date:** [April 6, 2006, 2:11am UTC](https://www.ruby-forum.com/t/howto-use-veriables-inside-of-regexp-and-commands/56959/1 "2006-04-06T02:11:11Z")

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Hi,

I’ve just started using Ruby and am LOVING IT! 😃

For my job I need to do allot of shell scripting but have been getting  
very annoyed at its limitations.

So I am now looking to Ruby to replace it. The thing is I need to be  
able to run a command say “ls” with a variable say “directory”. Heres an  
example of what I would do in shell script.

$directory="/tmp"

ls $directory

Now in Ruby I have to use the backquotes for commands right? So if I  
create a variable directory in Ruby how do I get it’s contents to be  
executed in the command or evaluated in a regular expression?

For example:

directory = “/tmp”

puts `ls directory`  
puts /directory/

I know the above is wrong and both will just evaluate the word directory  
not the variables contents. So how do I get the contents in there?

Thank you very much for you help.

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<div class="post-metadata">

**Author:** ![pyr0](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/da6949/32.png) [@pyr0](https://www.ruby-forum.com/u/pyr0)\
**Post date:** [April 6, 2006, 2:30am UTC](https://www.ruby-forum.com/t/howto-use-veriables-inside-of-regexp-and-commands/56959/2 "2006-04-06T02:30:30Z")

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Have you tried just using

Dir.entries(’/path/to/dir’).each {|entry| puts entry}?

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<div class="post-metadata">

**Author:** ![pyr0](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/da6949/32.png) [@pyr0](https://www.ruby-forum.com/u/pyr0)\
**Post date:** [April 6, 2006, 2:52am UTC](https://www.ruby-forum.com/t/howto-use-veriables-inside-of-regexp-and-commands/56959/3 "2006-04-06T02:52:41Z")

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Nope but unfortunately that only gives me solution to one situation 😕

There are allot of other times I’ll want to run a different command with  
varying input.

Is there no escape character or anything that can bee used?

Also on these forums wheres the reply button? I Could only find the  
reply with quote one?

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<div class="post-metadata">

**Author:** ![pyr0](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/da6949/32.png) [@pyr0](https://www.ruby-forum.com/u/pyr0)\
**Post date:** [April 6, 2006, 4:04am UTC](https://www.ruby-forum.com/t/howto-use-veriables-inside-of-regexp-and-commands/56959/4 "2006-04-06T04:04:53Z")

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Awesome thanks to you both 🙂

Craig your answer is exactly what I was looking for 🙂

And thanks to you Keith I have another very interesting class to look at  
😉

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<div class="post-metadata">

**Author:** ![pyr0](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/da6949/32.png) [@pyr0](https://www.ruby-forum.com/u/pyr0)\
**Post date:** [April 6, 2006, 3:40am UTC](https://www.ruby-forum.com/t/howto-use-veriables-inside-of-regexp-and-commands/56959/5 "2006-04-06T03:40:02Z")

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To answer the original question, you can embedded any variables or  
expressions in #{exp}. In your example, you can say:

directory = ‘/tmp’  
puts `ls #{directory}`  
if ‘/tmp/junk’ =~ /^#{directory}/

If you are interested in getting directory entries, Keith’s excellent  
suggestion is what you should consider.

Hope it helps!

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<div class="post-metadata">

**Author:** ![pyr0](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/da6949/32.png) [@pyr0](https://www.ruby-forum.com/u/pyr0)\
**Post date:** [April 6, 2006, 8:20pm UTC](https://www.ruby-forum.com/t/howto-use-veriables-inside-of-regexp-and-commands/56959/6 "2006-04-06T20:20:31Z")

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On Apr 5, 2006, at 10:04 PM, Karl Bennett wrote:

> 

Note that puts `command` is sort of redundant, if you don’ want to  
store the results in the string

system(“command”) will send the output to the standard output,  
without allocating a big string. Other methods you may want to look  
into are IO.popen .