BuiltIn Functions

1
Built-In Functions
2
Notations

• For each function, I will give its name and
  prototype.
• prototype number and type of arguments
• ARRAY means an actual named array (i.e., variable
  starting with _at_)
• LIST means any list of elements (i.e., a list
  literal or a named array)
• HASH means a named hash variable ()
• other types will identify the purpose of a scalar
  value

3
push ARRAY, LIST

• add values of LIST to end of ARRAY
• push _at_array, 5
• adds 5 to end of _at_array
• push _at_foo, (4, 3, 2)
• adds 4, 3, and 2, to the end of _at_foo
• _at_a (1, 2, 3) _at_b (10, 11, 12)
• push _at_a, _at_b
• _at_a now ? (1, 2, 3, 10, 11, 12)

4
pop ARRAY

• remove and return last element of ARRAY
• _at_array (1, 5, 10, 20)
• last pop _at_array
• last ? 20
• _at_array ? (1, 5, 10)
• _at_empty ()
• value pop _at_empty
• value ? undef.

5
unshift ARRAY, LIST

• Add elements of LIST to front of ARRAY
• unshift _at_array, 5
• adds 5 to front of _at_array
• unshift _at_foo, (4, 3, 2)
• adds 4, 3, and 2, to the front of _at_foo
• _at_a (1, 2, 3) _at_b (10, 11, 12)
• unshift _at_a, _at_b
• _at_a now ? (10, 11, 12, 1, 2, 3)

6
shift ARRAY

• remove and return first element of ARRAY
• _at_array (1, 5, 10, 20)
• first shift _at_array
• first ? 1
• _at_array ? (5, 10, 20)
• _at_empty ()
• value shift _at_empty
• value ? undef

7
splice ARRAY, OFFSET, LENGTH, LIST

• functionality of push, pop, shift, unshift
• (plus a little bit more)
• remove LENGTH elements from ARRAY, starting at
  position OFFSET, and replace them with LIST.
• In scalar context, return last element removed
• In list context, return all elements removed
• _at_foo (1 .. 10)
• _at_a splice _at_foo, 4, 3, a .. e
• _at_foo ? (1, 2, 3, 4, a, b, c, d, e, 8,
  9, 10)
• _at_a ? (5, 6, 7)

8
splice w/o some arguments

• splice ARRAY, OFFSET, LENGTH, LIST
• Omit LIST remove elements, dont replace
• Omit LIST and LENGTH remove all elements
  starting at OFFSET
• Omit LIST, LENGTH, and OFFSET clear entire ARRAY
  as its being read

9
splice equivalencies

• splice ARRAY, OFFSET, LENGTH, LIST
• push _at_a, (x, y)
• splice (_at_a, _at_a, 0, x, y)
• pop _at_a
• splice (_at_a, a) remove last element
• splice (_at_a, -1)
• shift _at_a
• splice (_at_a, 0, 1) remove first element
• unshift _at_a, (x, y)
• splice (_at_a, 0, 0, x, y)
• ax y
• splice (_at_a, x, 1, y) insert at position x

10
keys HASH values HASH

• keys ? return list of all keys from HASH
• seemingly random order
• values ? return list of all values from HASH
• same random order as keys produces
• Example hash
• months (Jan gt January, Feb gt
  February, Mar gt March, )
• keys (months) ? (Jan, Feb, Mar, )
• values (months) ? (January, February,
  March, )
• NOT necessarily in that order.

11
length EXPR

• return number of characters in EXPR
• a Hello\n
• b length a
• b ? 6
• Cannot use to find size of array or hash

12
index STR, SUBSTR, OFFSET

• Look for first occurrence of SUBSTR within STR
  (starting at OFFSET)
• OFFSET defaults to 0 if omitted
• Return first position within STR that SUBSTR is
  found.
• a index Hello World\n, o
• b index Hello World\n, o, a1
• a ? 4, b ? 7
• Returns -1 if SUBSTR not found.
• rindex ? return last position found

13
reverse LIST

• in list context, return an array consisting of
  elements in LIST, in opposite order
• _at_foo (1 .. 10)
• _at_bar reverse _at_foo
• _at_foo ? (1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
• _at_bar ? (10, 9, 8, 7, 6, 5, 4, 3, 2, 1)
• in scalar context, take LIST, concatenate all
  elements into a string, and return reverse of
  that string
• rev reverse _at_foo
• rev ? 01987654321

14
stat FILEHANDLE

• Return a 13-element list containing statistics
  about file named by FILEHANDLE
• can also be used on a string containing a file
  name.
• (dev, ino, mode, nlink, uid, gid, rdev,
  size, atime, mtime, ctime, blksize, blocks)
  stat filename
• See Camel page 801 for full description
• Common uses
• _at_info stat file
• print File size is info7, last access time is
  info8, last modified time is info9\n

15
sort LIST

• returns LIST sorted in ASCIIbetical order.
• undef comes before , then sort by ASCII chart
• does not affect LIST that is passed in
• note that by ASCII chart, 100 comes before 99
• _at_f (Banana, Apple, Carrot)
• _at_sorted sort _at_f
• _at_sorted ? (Apple, Banana, Carrot)
• _at_f unmodified
• _at_nums (97 .. 102)
• _at_s_nums sort _at_nums
• _at_s_nums (100, 101, 102, 97, 98, 99)

16
Advanced Sorting

• You can tell sort how you want a function sorted
• Write a small function describing the sort order
• In this function, Perl will assign a and b to
  be two list elements.
• If you want a to come before b in sort order,
  return 1. If you want b first, return 1.
• if order of a and b doesnt matter, return 0
• sub numeric_sort
• if (a lt b) return 1
• elsif (a gt b) return 1
• else return 0

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Using Your Own Sort

• Now that we have that function, use it in sort
• _at_nums (4, 2, 9, 10, 14, 11)
• _at_sorted sort numeric_sort _at_nums
• _at_sorted ? (2, 4, 9, 10, 11, 14)
• Look at that function again
• if (a lt b) return 1
• elsif (a gt b) return 1
• else return 0
• This can be simplified quite a bit.
• return (a ltgt b)

18
Simplifying Further

• We now have
• sub by_number
• return (a ltgt b)
• When sort function is that simple, dont even
  need to declare it
• _at_sorted sort a ltgt b _at_nums
• Excellent description of sorting in Llama chapter
  15

19
Exercises for the Reader

• How might you sort in reverse numeric order?
  i.e. (102, 101, 100, 99, 98, 97)
• without using the reverse function
• How would you sort in reverse ASCIIbetical order?
  ie (dog, cat, bear)
• without using the reverse function
• How would you get an array consisting of keys of
  a hash table sorted by key?
• How would you get an array consisting of keys of
  a hash table sorted by value?