Ruby Programming Tutorial - 23 - Beginning Regular Expressions Video Lecture | Introduction to Coding with Ruby - Back-End Programming

what is going on guys welcome to your
23rd Ruby tutorial and in this lesson I
want to start talking to you guys about
something called regular expressions now
what regular expressions are are
basically an awesome way that you can
work with character patterns and text
patterns and Ruby and actually regular
expressions isn't just part of Ruby it's
a different computer science topic
altogether and a bunch of different
programming languages use regular
expressions in Ruby is one of the best
whenever working with these regular
expressions so even though it is
specific only to Ruby it's important to
learn it nonetheless so let me go ahead
and show you guys an example before I
jump right into learning what these
regular expressions are and the
different types of regular expressions I
want to show you guys a simple example
of when you would use it so let me go
ahead and type I'm just printing
something out on the screen puts
something like fat Bucky not very nice
but it'll be good for this example and
I'm going to use the sub method now this
method again this isn't a regular
expression but this is an example of
when you could use a regular expression
say you wanted to take the string fat
Bucky and you wanted it to change out
the word fat for something a little bit
nicer because you know I just think it
would be a good idea so what we want to
do is we want to give it two parameters
first the string that we want to
substitute which is fat and second the
string that we want to substitute it for
which is lucky so instead of fat Bucky
we want to change out the word fat for
lucky hit enter and now says lucky Bucky
so another thing that I want to take
note of is whenever you use the sub
method what it does is it only replaces
the first instance of the word fat so if
you have fat Bucky fat and you try to
run this baby check it out it only
replaces the first fat so lucky Bucky
fat but what if you want to replace all
the fats not just the first one well in
order to do that you need to use the G
sub method why they named it G sub I'm
not entirely sure but what this does is
instead of just substituting the first
fat it substitutes all the fats so go
hadn't hit Enter lucky lucky lucky there
we go
I am NOT fat I don't know I don't know
where I'm going with this one but so
anyways this is basically a simple
substitution method and this is
basically what regular expressions can
do they can take part of your text and
they can either swap it out for
something else or they can just give it
to you for later so even though we use
the regular method in this example I'm
going to show you guys how to do this
with regular expressions so let's go
ahead and use a regular expression now
go ahead and make a simple string
variable actually it doesn't matter at
all what you write but like yo what the
heck do you want that's the first thing
that came into my mind I have no idea
why so basically we have a string
variable and we stored it in the
variable a and it says yo what the heck
do you want so now what we want to do is
say that we want to rip out the first
two characters and replace it with
something a little bit nicer so instead
of saying yo that's kind of you know
ghetto and inappropriate we might want
to say excuse me sir so here's how we
would do that using regular expressions
so let me go ahead and write puts
because we want to print something out
on the screen a sub now instead of just
substituting something for something
else what we want to do is this we want
to start off by passing in the first
parameter which is a regular expression
now remember in the sub method you the
first thing you write is what do you
want to replace what thing do you want
to get rid of well what we want to do is
we want to get rid of the first two
characters now in order to write this
using regular expressions we do this in
between two forward slashes we write I
believe that's called the carrot and the
carrot is the symbol above the six on
your keyboard looks like a little up
arrow and two little dots now let me go
ahead and finish this and then I'll
explain it excuse me sir so basically
what we did is instead of writing a
string that we want to substitute
substitute for example
why oh we gave a regular expression
instead now before I you know keep
talking let me go ahead and run this and
make sure it works so now it says excuse
me sir what the heck do you want what
you know still isn't the nicest thing
but it's a little bit better than yo
what the heck do you want now let me
talk to you guys about this regular
expression a little bit regular
expressions are basically using weird
symbols to symbolize characters so
basically what this regular expression
does is it replaces the first two
characters of a string so anytime you
use regular expressions and I'll be
talking about it later on and it's going
to clear everything up but anytime we're
going to be working with regular
expressions you always put your special
symbols in between forward slashes so it
always starts with a forward slash and
ends with a forward slash anything in
between is the stuff that we need to
interpret so let's go ahead and
interpret this one real quick the little
carrot I think it's called the carrier
if I'm wrong then someone correct me in
the comments section below
but the little symbol above the six on
your keyboard is called an anchor in
regular expressions what this means is
we basically want to match starting from
the beginning of a string so that's why
it took the excuse me sir and it didn't
replace it with the heck it didn't
replace it with want it started with the
yo since yo was at the beginning of the
string now these two little dots right
here dots basically symbolize any
character so whenever we use dot in
regular expressions it took the first
two characters no matter what they were
and it replaced it with excuse me sir so
basically in plain simple English we're
saying this okay what we want to do is
we want to rip out the first two
characters starting at the beginning of
the string and in their place we want to
stick in excuse me sir and we did that
in our end result instead of yo what the
heck do you want was excuse me sir what
the heck do you want so I know at first
glance regular expressions can seem very
confusing and they are but in the next
couple tutorials I'm going to be showing
you guys the different ways you can plug
in regular expressions in rubies and
also teaching guys about a couple
different symbols and when you guys are
done watching like the next three or
four tutorials you guys are going to be
pros on regular expressions but for now
thank you guys for watching don't forget
subscribe and I'll see you guys in the
next video