PERL

1
PERL

• By C. Shing
• ITEC Dept
• Radford University

2
Objectives

• Understand the history
• Understand constants and variables
• Understand operators
• Understand control structures
• Understand functions
• Understand file I/O
• Understand command line arguments
• Understand how to use Perl for system
  administration

3
History

• Perl (Practical Extraction Report Language) by
  Larry Wall (1986)
• Language between C and shell Scripting , need
  interpreter
• Provide File access and Unix utilities
• Download site http//www.perl.com
• File extension (.pl)
• Interpret with error message
• perl -w filename.pl arg0 arg1
• Artistic license variation of GNU public
  license, free

4
Constants

• Scalar
• Number integer, real, scientific notation
• String within
• Boolean
• 1 represents true
• 0 represents false

5
Variables

• Scalar begin with
• Number integer, real
• String string, character
• Array begin with _at_
• Index starts from 0
• Associative begin with
• use hash

6
Control Structures

• Print
• Assignment
• Conditional
• Loop
• Function (Subroutine)

7
Control Structures - Print

• Syntax each statement ends with
• Print variable constant
• Example
• print "Please enter a number"

8
Control Structures - Assignment

• Syntax each statement ends with
• Variable expression
• Comment begins with

9
Control Structures - Assignment

• Scalar Variable
• Number integer, real
• Example
• i5
• j-6.2
• String string, character
• Example
• monthJanuary
• char\t

10
Control Structures - Assignment

• Scalar Variable
• Number integer, real
• Example
• i5
• j-6.2
• number ltSTDINgt (keyboard input)
• String string, character
• Example
• monthJanuary
• char\t
• guess ltSTDINgt (keyboard input)
• fileString ltFILEHANDLEgt (getting data
  from file)

11
Control Structures - Assignment

• Array Variable
• Example
• _at_array ("john", "susan", "david", "sarah",
  "ryan", "laura")
• _at_numRange (1..6)
• Where
• array0 john
• array1 susan
• array5 laura

12
Control Structures - Assignment

• Associative Variable
• Example
• hash ("smith"gt"john", "sides"gt "susan",
  "davis"gt"david", "star"gt"sarah",
  "rush"gt"ryan","lane"gt "laura")
• Where
• arraysmith john
• arraysides susan
• arraylane laura

13
Operators Arithmetic, Logic, Relational

• Arithmetic ,-,,/
• Logical ,
• Relational
• Numeric , !, gt, gt, lt, lt
• String eq, ne, gt, ge, lt, le

14
Operators - String

• String
• Concatenation .
• Example
• month month.char
• message "This is a number ".\t.number.
  "\n"
• Match
• Example
• line s/the/THE/g (replace all the by THE
  in the line)
• line /(\w)(\s)(\w)(\s)/ (line that
  matches the pattern word, spaces, word

15
Control Structures - Conditional

• Syntax
• If (condition)
• If (condition)
• else
• If (condition1)
• elsif (condition2)
• else

16
Control Structures - Conditional

• Example
• if (guess eq "hello")
• print "The word ".guess." that you guessed
  is correct.\n\n"

17
Control Structures - Conditional

• Example
• if (avg gt0.895avgall)
• grade"A"
• elsif (avg gt0.795avgall)
• grade"B"
• elsif (avg gt0.695avgall)
• grade"C"
• elsif (avg gt0.595avgall)
• grade"D"
• else

18
Control Structures - Loop

• While
• Until
• Foreach
• For

19
Control Structures While Loop

• Syntax
• while (condition)
• when condition is false, exit loop

20
Control Structures While Loop

• while (lineltUSERFILEgt)

21
Control Structures Until Loop

• Syntax
• until (condition)
• when condition is true, exit loop

22
Control Structures Until Loop

• Example
• until (array20 eq "listing")

23
Control Structures Foreach Loop

• Syntax
• foreach variable (variableRange)
• when variable is outside of variableRange, exit
  loop

24
Control Structures Foreach Loop

• Example
• foreach month (1..12)

25
Control Structures For Loop

• Syntax
• for (initialization condition ending body
  stmt)
• when condition is false, exit loop

26
Control Structures For Loop

• Example
• for (i1 ilt12 i)

27
Control Structures - Function (Subroutine)

• Library function
• User (-defined) function

28
Control Structures Library Function

• lc() or lc convert to lower case
• uc() convert to upper case
• open(), close(), die(), exit(), last() See File
  I/O
• print()
• length() length of string
• index()

29
Control Structures Library Function

• Example
• search item through list
• foreach user (_at_list)
• if (user eq lc(item))
• user_correct 1
• foreach

30
Control Structures Library Function

• keys() gives the key value of the hash
• chomp() delete the new line character from
  variable
• split (delimiter, variable) split a variable
  using delimiter
• my() create local variable
• shift (arrayName) get rid of 1st element in the
  arrayName
• push (array1, array2) push array2 to the end of
  array1

31
Control Structures Library Function

• Example
• while (lineltNAMEFILEgt)
• chomp(line)
• username are separated by space(s)
• _at_arraysplit /\s/, line

32
Control Structures Library Function

• Example
• foreach userkey (keys hash)
• if (hashuserkey eq lc(name))
• user_correct 1
• lastnameuserkey
• foreach

33
Control Structures User Function

• Function call
• Syntax
• functionname (actualParameterList)
• Example
• check (name, _at_array)

34
Control Structures User Function

• Function definition
• Syntax
• sub functionname
• my localVar1 _0
• my localVar2 _1
• my _at_localArray _at__

35
Control Structures User Function

• Function definition
• Example
• check (name, _at_array)
• sub check
• the following 3 lines declare local
  variables
• my item _0
• my _at_list _at__
• my user_correct 0

36
Control Structures User Function

• Example
• printArray(_at_array)
• sub printArray
• _at_array is a local variable in the sub
• my _at_array _at__
• foreach cell (_at_array)
• print cell."\t"
• print "\n"
• sub printArray

37
File I/O

• Open/Close file
• Syntax
• open (FILEHANDLE, ltfilename)
• close (FILEHANDLE)

38
File I/O

• Open/Close file
• Example
• read all names into _at_array from input data
  file sixth2.txt
• open (NAMEFILE, "ltsixth2.txt")
• die "Error Unable to open the file !"
• open output file for print
• open (OUTFILE,"gtattend.txt")
• print OUTFILE "Lastname\t\tFirstname\t\tE-Mail
  Name\n"

39
Command Line Arguments

• perl w filename.pl arg0 arg1 arg2
• Arg0, arg1 and arg2 are command line arguments
• Inside the program, they are stored in array _at_ARGV

40
Command Line Arguments

• Example
• open (USERFILE, "ltuserARGV0.txt") die
  "Error Unable to open the file !"
• open (OUTFILE,"gtattendARGV0.txt")
• print OUTFILE "Library Attendance for ITEC
  100-ARGV0\n\n"

41
System Administration

• Call system library when using shell commands in
  Perl
• Give full path name for shell commands
• Use which command to find full path name
• Watch for reserved names in Perl

42
System Administration

• Example Run Perl in Unix environment
• system("/usr/local/gnu/bin/awk 'print
  \1,\2,\9' temp1.txt gt temp2.txt")
• system("/usr/bin/rm -f temp2.txt")
• If you run Perl in Unix, make sure to change data
  into Unix format, such as
• system("/usr/bin/dos2unix session.txt
  session.txt")

43
Reference

• Some simple examples