System Administration Introduction to Scripting, Perl Session 5

1
System AdministrationIntroduction to Scripting,
PerlSession 5 Fri 23 Nov 2007

• References
• Perl man pages
• Albert Lingelbach, Jr.
• alingelb_at_yahoo.com

2
Review

• Intro to shell
• Intro to perl
• Questions from exercises ?

3
Arrays introduction

• Arrays store a series of values that can be
  accessed by "index"
• Index is an integer
• starting at 0 or 1 Perl array indexing starts at
  0
• the upper limit depends on the language or
  computer
• In Perl, array variables begin with _at_
• Example my _at_namearray
• To access an element namearrayi
• Example namearray 3 "testing"

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Arrays initialization

• The contents of an array can be initialized at
  declaration
• my _at_namearray ("geoff", "foibe", "oscar")
• This is equivalent to
• my _at_namearray
• namearray0 "geoff"
• namearray1 "foibe"
• namearray2 "oscar"

5
Arrays size

• The index of the last element can be found using
  the expression
• array
• Notice that this is a scalar expression
• What is an expression that will return how many
  elements are in an array ?
• What statements will print out every element of
  an array ?

6
Arrays practicum

• Number of elements in an array
• array 1
• _at_array in scalar context
• Print every element of an array
• for (my idx 0 idx lt _at_array idx)
• print "arrayidx arrayidx\n"

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Arrays multiple dimensions

• Arrays can have more than one dimension
• my _at_gameboard ((" ", " ", " "), (" ", " ", "
  "), (" ", " ", " ") )
• gameboard 1, 1 "X"
• gameboard 0, 0 "O"
• gameboard 1, 2 "X"
• gameboard 1, 0 "O"

8
Arrays miscellaneous

• An array can be sorted
• my _at_sorted sort _at_myarray
• An array can be reversed
• my _at_reversed reverse _at_myarray
• Seeman -M /usr/perl5/man perldatafor more
  information

9
Hashes introduction

• Hashes store a series of values that can be
  accessed by "key"
• Key is a scalar (string, number) which is unique
  among the set of keys in the hash
• Value is another scalar, associated with the key
• Hashes begin with
• Example my phonebook
• To access an element hashkey
• Example phonebook "mangula"

10
Hashes initialization

• The contents of a hash can be initialized at
  declaration
• my phonebook (
• "albert" gt "0787487449",
• "mangula" gt "0756181255" )
• This is equivalent to
• my phonebook
• phonebook "albert" "0787487449"
• phonebook "mangula" "0756181255"

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Hashes useful functions

• The set of keys in a hash
• my _at_keys keys myhash
• The set of values in a hash
• my _at_values values myhash
• Expression to return the number of elements in a
  hash ?
• Code to display the contents of a hash ?

12
Hashes practicum

• Number of elements in a hash
• my _at_arr keys hash
• my length _at_arr
• my length arr 1
• Display contents of a hash
• my _at_keys keys hash
• for (my idx 0 idx lt _at_arr idx)
• print "hash keys idx " ."hash keys
  idx\n"

13
Hashes miscellaneous

• Seeman -M /usr/perl5/man perldatafor more
  information

14
Regular Expressions introduction

• Regular expressions (sometimes shortened to
  "regexp"s) are used for matching text to patterns
• Recall shell "wildcards" ?
• Excellent for searching, data validation

15
Regular Expressions statement syntax

• "Matching" operator
• Pattern markers / /
• Example
• if (s /pattern/)
• print "s matches pattern\n"
• else
• print "s does not match pattern\n"

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Regular Expressions pattern syntax

• any letter or number character represents itself
• "abc" matches /abc/
• or one of many sub-patterns
• () group sub-patterns
• "one" or "two" or "three" match /(onetwothree)/
• "one" matches /(one)/, /(on)(e)/
• group single character options
• "a" or "b" or "c" match /abc/
• "af" or "ag" match /abcfgh/
• "ab" does not match /abcfgh/

17
Regular Expression pattern syntax continued

• not in set
• "a" or "b" matches /fgh/
• "f" does not match /fgh/
• Placement
• beginning of string
• end of string
• "abc" matches /abc/, /abc/, /abc/, /abc/
• "xabc" matches /abc/, /abc/
• "xabc" does not match /abc/ or /abc/
• "abcx" matches /abc/, /abc/
• "abcx" does not match /abc/, /abc/

18
Regular Expression pattern syntax continued

• Quantifiers
• ( )? zero or one
• "caa", "abad" match /ab?a/
• "abba" does not match /ab?a/
• "acb", "yafoob3" match /a(foo)?c/
• "afoofooc" does not match /a(foo)?c/
• ( ) zero or more
• "xaa", "yabbbbbbba" match /aba/
• ( ) one or more
• "aa", "abbbb" do not match /aba/

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Regular Expression pattern syntax continued

• More quantifiers
• ( )n exactly n occurrences
• "afoofoofoob" matches /a(foo)3b/
• "afoofoob" does not match /a(foo)3b/
• ( )i, j between i and j occurrences
• "afoobarbarb" matches /a(foo)1,3(bar)2,4b/
• "afoobarbarb" does not match /a(foo)2,3(bar)2,4
  b/
• ( )i, i or more occurrences
• "afoob" does not match /a(foo)2,b/
• "afoofoofoofoofoofoob" does match /a(foo)2,b/

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Regular Expression pattern syntax continued

• \ is "escape" character
• use in front of special character to match it
  literally
• "a(b" matches /a\(b/
• /ab/ is not a correct regular expression
• use as marker for pre-defined sets/patterns (next
  slide)?
• . (dot, period) matches any one character
• "abb", "a(b" match /a.b/
• "abx" does not match /a.b/

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Regular Expression pattern syntax continued

• Pre-defined patterns
• \s whitespace (space, tab, newline)?
• \S non-whitespace character (same as \s)?
• \d digit
• \w word character (a-z, A-Z, 0-9, _)?

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Regular Expressions miscellaneous

• There are more pre-defined characters
• There are more features
• For more informationman -M /usr/perl5/man
  perlrequickman -M /usr/perl5/man perlretutman
  -M /usr/perl5/man perlre

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Review

• Arrays _at_array ("zero", "one", "two")
  arrayidx array sort _at_array reverse
  _at_array
• Hashes hash ("a" gt 1, "b" gt 2)hash
  keykeys hash values hash
• Regular expressions // . ? ()
  ,

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Next up

• Process management
• No class until January
• See e-mail for exercises
• e-mail any questions