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dollar sign here at the end that does
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not mean I want the user to type a
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carrot symbol or a dollar sign this is
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special symbology that indicates to re.
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search that it should only look for now
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an exact math against this pattern so if
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I now go back to my terminal window and
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I'll leave the previous result on the
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screen let me type the exact same thing
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my email address is maen harvard.edu
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enter sorry period and now I'm going to
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go ahead and hit enter now that's
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considered invalid but let me clear the
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screen and just to make sure I didn't
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break things let me type in just my
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email address and that too is valid any
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questions now on this version of my
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4.841
regular expression which note goes
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further to specify even more precisely
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that I want it to match at the start and
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the
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end any questions on this one here okay
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you have slash and that edu and then the
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dollar sign but the dot is like uh one
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of the regular expression right it
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normally is but this backslash that I
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deliberately put before this period here
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is an escape character it is a way of
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telling re. search that I don't want any
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character there I literally want a
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period there and it's the only way you
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can distinguish one from the other if I
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got rid of that slash this would mean
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that the email address just has to end
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with any character then an e then a d
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then a u i don't want that I want
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literally a period Then the E then the D
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then the U this is actually common
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convention in programming and technology
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in general if you and I decide on a
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convention whereby we're using some
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character on the keyboard to mean
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something special invariably we create a
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future problem for oursel when we want
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to literally use that same character and
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so the solution in general to that
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problem is to somehow escape the
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character so that it's clear to the
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3.121
computer that it's not that special
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4.32
symbol it's literally the symbol it sees
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so we don't need another we don't need
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another another slash before the dollar
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sign no uh because in this case dollar
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sign means something special per this
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chart here dollar sign by itself does
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not mean US dollars or currency it
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4.28
literally means match the end of the
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string if however I wanted the user to
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literally type in a dollar sign at the
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end of their input the solution would be
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the same I would put a backslash before
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the dollar sign which means my email
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address would have to be something like
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maen harvard.edu dollar sign which is
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obviously not correct too so backslashes
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just allow you to tell the computer to
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not treat those symbols specially like
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meaning something special but to treat
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them literally instead how about one
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other question here on regular
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4.4
Expressions you said you said one
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represents to to make it one plus then
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you say one was to make it one with
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nothing sure let me rewind in time I
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think what you're referring to was one
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of our earlier versions that initially
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looked like this which just meant Zero
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5.24
or more characters than an at sign than
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zero or more other characters we then
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evolved that to be this do Plus on both
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sides which means one or more characters
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on the left then an at sign then one or
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more characters on the right and if I'm
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4.08
interpreting your question correctly one
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of the points I made earlier was that if
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you didn't use Plus or forgot that it
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exists you could equivalently achieve
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the exact same result with two dots and
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a star because the first dot means any
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5.04
character it's got to be there the
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5.4
second dot star means zero or more other
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5.48
characters and same on the right so it's
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just another way of expressing the same
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idea one or more can be represented like
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this with DOT do star or you can just
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use the handier syntax of plus which
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means the same thing all right so I dare
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say there's still some problems with the
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regular expression in this current form
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because even though now we're starting
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