Whats a Scalar

1
Whats a Scalar?

• Simplest kind of data Perl manipulates
• Either a number or a string of characters (Perl
  uses them interchangeably)
• Can use operators on scalars, usually generating
  another scalar
• Can store scalar value into scalar variable

2
Scalar Variables ()

• To assign into a scalar variable, use a sign
• foo 27 a scalar number
• bar 'Joel Grow' a scalar string

3
Numbers

• 3
• -9000000000000
• 3.1415926536
• 3.46e10
• For the C geeks/curious really all are
  internally double precision floats

4
Numerical Operators

• 2 3
• 5.1 - 2
• 3 12
• 10.2 / 3
• 2 3
• 10 3

5
Strings

• Sequences of 0 or more characters
• ""
• 'Joel'
• "This is a long string with numbers 8 1 33 and
  !_at__at_ characters"
• Any character (8 bit, 0 thru 256)
• Not just ASCII 32 thru ASCII 126
• Can be single quoted or double quoted

6
Single-Quoted Literal Strings

• Does NOT do variable interpolation--treats the
  string as literal
• 'camel' five chars, 'c', ..., 'l'
• 'don\'t' includes single quote char
• '' null string, no chars
• 'a\\b' 'a', '\', 'b'

7
Double Quoted Literal Strings

• DOES do variable interpolation
• backslashes are special
• "big camel\n" 2 words and a newline
• "bond \007" 007 is bell char in octal
• "coke\tsprite" tab between words
• "\cGding" bell char (ctrl-C) and ding
• "a\\b" 'a', '\', 'b'
• "c\temp" what's this?
• "hello foo\n" replaces foo with it's value

8
Operators for Strings

• "tall" . " turtle" concatenation
• 'what "color" is that?' . "\n"
• "a" . " " . "b"
• a eq 'bcd'
• f ne g
• g gt "mcgd"
• jake lt fred
• a le b
• c ge d
• (32) x 4 is "5555
• "-" x 50 is what?

9
Numeric vs String comparisons...

• Context is very important in comparisons!
• a 5
• b 16
• c 'joelg'
• d 'joel'
• if ( a lt b ) numeric, true
• if ( a lt b ) string, false
• if ( c gt d ) string, true
• if ( c gt d ) numeric, false

10
More on numeric vs. string comparisons

• Here's a common gotcha, using instead
• of eq, (or vice versa)
• a 5
• b 16
• c 'joelg'
• d 'joel'
• if ( c d ) numeric, true!
• if ( c eq d ) string, false

11
Alternative Quotes

• Can use q like single quotes and qq like
  double quotes
• you can actually use any matchable delimiter (
  ) ltgt
• qhello 'world'!
• qqhello foobar!
• qA 'starring' \role\
• qqDon't "quote" me!
• qltDon't "quote" me!gt

12
Assigning into a variable

• one 1
• two 2.0
• first_name "Joel"
• last_name 'Grow'
• another_one one
• copy_last_name last_name

13
Controlling Case examples

• big uc('hello') HELLO
• little lc('WorlD') world
• big "\Uhello" HELLO
• big "\uhELLo" HELLo
• little "\LWorlD" world
• little "\lwORLD" wORLD
• beast "dromedaRY"
• capitalize ucfirst(beast) DromedaRY
• capitalize "\u\Lbeast" Dromedary

14
Here Documents

• Can print multi-line string easily
• print ltltEnd_of_HTML
• ltHTMLgt
• ltBODYgt
• ltTABLEgtltTRgtltTDgtHello world!lt/TDgtlt/TRgt
• lt/TABLEgt
• lt/BODYgt
• lt/HTMLgt
• End_of_HTML

15
Scalar Operators and Functions

• a 4
• b a 3
• b b 2
• d (c 4) assign 4 to c and d
• d c 4 same thing
• b 4 (a 3) what is a? b?
• Note, just because you can do something in
• Perl doesn't always mean you should. That
• last line is not very obvious to the code
• reader.

16
Binary Assignment Operators

• a 3 same as a a 3
• b - 1 b b - 1
• d / 3 d d / 3
• r 4 r r 4
• b (a 4) valid, but weird.
• Please don't do this

17
More binary assignment

• concatenate
• str . 'foobar'
• same as str str . 'foobar'

18
Autoincrement/autodecrement

• means 'add one' -- means 'subtract one'
• a 2
• a same as a a 1, a now equals 3
• pre and post increment
• print a prints 3, changes a to 4
• print a prints 5, a now 5
• print --a prints 4, a now 4
• print a-- prints 4, a now 3

19
Scalar Interpolation

• a "joel"
• this will print "hi joel!" and a newline
• b "hi a!\n"
• c "no such variable foo\n"
• if foo is undefined then c is
• "no such variable \n"

20
More scalar interpolation

• x 'fred'
• y "hey x" y is 'hey fred'
• if you don't want interpolation
• z "hey \x"
• z is what?

21
More scalar Interpolation

• we want to assign "It's payday" to barney
• fred "pay"
• fredday "Monday"
• barney "It's fredday!"
• what is barney?

22
More scalar interpolation

• fred "pay"
• fredday "Monday"
• use if needed
• barney "It's fredday!" Its payday!
• or do this
• barney "It's fred"."day!"

23
Chop

• chop removes (and returns) the last
• character in a string.
• x "hello world"
• chop(x) x is now "hello worl"
• last_char chop(x) what is last_char?
• x chop(x) replaces x with its last
• character. weird but valid

24
Chomp

• var "abc\n"
• chomp(var) var becomes "abc"
• chomp only removes the "record separator
• character", usually a newline.
• It's a safe chop.
• chomp is much more common than chop.
• you will probably use chomp a lot and chop
• very little, if ever

25
Scalar ltSTDINgt

• Reads input from the user
• (on the STDIN filehandle--more on filehandles in
  a few weeks)
• x ltSTDINgt wait for user to type
• something...
• chomp (x) get rid of newline
• or, do above in one step
• chomp (x ltSTDINgt)
• print "You just typed 'x'\n"

26
Scalars in Action
my name "Joel Grow" my email 'joelg' my
age 28 my GPA 3.72 if ( GPA gt 3 )
print "Good job name!\n" print "I'll send
email to email.\n" else print "You need
to study more name!\n"
27
Where do we go from here?

• Arrays--a big ol' list of scalars!