# Backticks

**URL:** <https://www.ruby-forum.com/t/backticks/112276>\
**Category:** Ruby\
**Created:** [August 17, 2007, 12:35am UTC](https://www.ruby-forum.com/t/backticks/112276 "2007-08-17T00:35:28Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![john\_old](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9f8e36/32.png) [@john\_old](https://www.ruby-forum.com/u/john_old)\
**Post date:** [August 17, 2007, 12:35am UTC](https://www.ruby-forum.com/t/backticks/112276/1 "2007-08-17T00:35:28Z")

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Wow, seems that you can use double-quoted string style substitution  
for backtick system calls.

say we make a list of some files:  
ls = Dir.glob(’\*.doc’)  
some\_file = ls[2]

on OS X there is the really convenient ‘open’ tool available at the  
command line for example.  
`open #{some_file}`

Whatever application is set to default for opening .doc files will be  
called to open the file.  
That’s not the point as much as system calls via back ticks can be  
sent variables and expressions from a Ruby script!  
Very convenient!

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**Author:** ![john\_old](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9f8e36/32.png) [@john\_old](https://www.ruby-forum.com/u/john_old)\
**Post date:** [August 17, 2007, 12:47am UTC](https://www.ruby-forum.com/t/backticks/112276/2 "2007-08-17T00:47:30Z")

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On Fri, Aug 17, 2007, John J. wrote:

> Whatever application is set to default for opening .doc files will be  
> called to open the file.  
> That’s not the point as much as system calls via back ticks can be  
> sent variables and expressions from a Ruby script!  
> Very convenient!

For added fun, try string interpolation inside regular expressions!

haystack = “foobarbaz”  
needle = “bar”

haystack =~ /#{needle}/  
=\> 3

yeah 😃

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**Author:** ![john\_old](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9f8e36/32.png) [@john\_old](https://www.ruby-forum.com/u/john_old)\
**Post date:** [August 17, 2007, 1:21am UTC](https://www.ruby-forum.com/t/backticks/112276/3 "2007-08-17T01:21:34Z")

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whoa, can you explain a little what’s going on here? I tried it and  
changed it around in irb but I can’t really figure out what’s going  
on.

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**Author:** ![john\_old](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9f8e36/32.png) [@john\_old](https://www.ruby-forum.com/u/john_old)\
**Post date:** [August 17, 2007, 2:08am UTC](https://www.ruby-forum.com/t/backticks/112276/4 "2007-08-17T02:08:38Z")

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Simon –

Being unsure of which part is confusing you, here’s a brief run-down:

If you place a statement between backticks (the little guys above the  
left tab on your keyboard) it will execute a command from the terminal  
and return the output. Try `ls` under OSX and `dir` under Windows. You  
can use `open` (osx) and `start` (win) to open a file with the default  
application for the file type.

In a double quoted string, you can put an object between #{} to  
dynamically build the string.  
For example –  
a = [‘Claire’, ‘Jennifer’, ‘Margaret’]  
a.each {|x| puts “Hello, #{x}”}

Very neat, and you can use it in all sorts of useful things.

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<div class="post-metadata">

**Author:** ![john\_old](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9f8e36/32.png) [@john\_old](https://www.ruby-forum.com/u/john_old)\
**Post date:** [August 17, 2007, 1:36am UTC](https://www.ruby-forum.com/t/backticks/112276/5 "2007-08-17T01:36:35Z")

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On 8/16/07, Simon S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> whoa, can you explain a little what’s going on here? I tried it and  
> changed it around in irb but I can’t really figure out what’s going  
> on.

#{} just happens to work more places than string literals:

If it helps clear it up, /#{needle}/ is roughly equivalent to

Regexp.new(“#{needle}”) which is sort of a silly use of interpolation,  
so let’s write it as:  
Regexp.new(needle)

So yeah, the string “bar” was used to construct the regexp /bar/.

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**Author:** ![john\_old](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9f8e36/32.png) [@john\_old](https://www.ruby-forum.com/u/john_old)\
**Post date:** [August 17, 2007, 3:27am UTC](https://www.ruby-forum.com/t/backticks/112276/6 "2007-08-17T03:27:42Z")

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On Aug 16, 2007, at 5:34 PM, John J. wrote:

> Whatever application is set to default for opening .doc files will  
> be called to open the file.  
> That’s not the point as much as system calls via back ticks can be  
> sent variables and expressions from a Ruby script!  
> Very convenient!

You can do these tricks even in languages that don’t support  
interpolation, as long as they allow you to set an environment variable.

James Edward G. II

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<div class="post-metadata">

**Author:** ![john\_old](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9f8e36/32.png) [@john\_old](https://www.ruby-forum.com/u/john_old)\
**Post date:** [August 17, 2007, 4:46am UTC](https://www.ruby-forum.com/t/backticks/112276/7 "2007-08-17T04:46:51Z")

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ahhh, haha. well, the part that got me was it returning a “3” because  
I just couldn’t find 3 instances of “bar” in there… then I realized,  
f-o-o-b. 0, 1, 2, 3. 😛