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comp.lang.ruby

backticks

John Joyce

8/16/2007 10:34:00 PM

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!
6 Answers

Ben Bleything

8/16/2007 10:46:00 PM

0

On Fri, Aug 17, 2007, John Joyce wrote:
> 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!

For added fun, try string interpolation inside regular expressions!

haystack = "foobarbaz"
needle = "bar"

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

yeah :D

Simon Schuster

8/16/2007 11:20:00 PM

0

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.

>
> For added fun, try string interpolation inside regular expressions!
>
> haystack = "foobarbaz"
> needle = "bar"
>
> haystack =~ /#{needle}/
> => 3
>
> yeah :D
>
>

Logan Capaldo

8/16/2007 11:36:00 PM

0

On 8/16/07, Simon Schuster <significants@gmail.com> 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/.

> >
> > For added fun, try string interpolation inside regular expressions!
> >
> > haystack = "foobarbaz"
> > needle = "bar"
> >
> > haystack =~ /#{needle}/
> > => 3
> >
> > yeah :D
> >
> >
>
>

Chris Worrall

8/17/2007 12:07:00 AM

0

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.

On 8/16/07, Logan Capaldo <logancapaldo@gmail.com> wrote:
> On 8/16/07, Simon Schuster <significants@gmail.com> 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/.
>
> > >
> > > For added fun, try string interpolation inside regular expressions!
> > >
> > > haystack = "foobarbaz"
> > > needle = "bar"
> > >
> > > haystack =~ /#{needle}/
> > > => 3
> > >
> > > yeah :D
> > >
> > >
> >
> >
>
>

James Gray

8/17/2007 1:27:00 AM

0

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

> 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!

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 Gray II

Simon Schuster

8/17/2007 2:46:00 AM

0

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. :P

On 8/16/07, Logan Capaldo <logancapaldo@gmail.com> wrote:
> On 8/16/07, Simon Schuster <significants@gmail.com> 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/.
>
> > >
> > > For added fun, try string interpolation inside regular expressions!
> > >
> > > haystack = "foobarbaz"
> > > needle = "bar"
> > >
> > > haystack =~ /#{needle}/
> > > => 3
> > >
> > > yeah :D
> > >
> > >
> >
> >
>
>