Perl Introduction

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Perl Introduction

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Functions from, C, sed, awk, and sh. Interpretive vs. Compiled Language. WWW Information ... nNbr1 = int 10 / 3; #Truncates. Example: numerics.pl. Page 21. List Values ... – PowerPoint PPT presentation

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Title: Perl Introduction

1
Perl Introduction
2
Perl Language

Practical Extraction and Report Language
Perl Language
Interpreted Language
Functions from, C, sed, awk, and sh
Interpretive vs. Compiled Language
WWW Information
http//www.perl.com

3
How to Obtain Perl

Get Perl Through WWW Using FTP
ftp ftp.CPAN.org
Name (ftp.CPAN.orgCPAN) anonymous
ftpgt cd pub/perl/CPAN/src
ftpgt binary
ftpgt get latest.tar.gz
ftpgt quit
Uncompress and Unpack
gunzip lt latest.tar.gz tar xvf -
cd perl5.004
sh configure make make test make
install

4
How to Obtain Perl (cont.)

Compile Perl Source code
Make executable visible to users

5
Perl Support

Perl Language
Freeware
Commercial versions
Perl Support
Corporate support
Web pages
Mailing lists
Usenet news
The Perl Journal

6
Running a Perl Program

Can be run from the command line
perl -e print Hello, world!\n
Can be run from a script
vi hello.pl
!/usr/bin/perl
print Hello, World!\n
chmod x hello.pl
hello.pl
Example hello.pl

7
Command Line Operations

Options on Command Line
perl options program
Options in a Script
! /usr/bin/perl options
! /usr/local/bin/perl in the Alcatel Environment
Options
-c Check syntax without execution
-d Run under Perl debugger
-e Execute line of script from command line
-h Summary of command line actions

8
Command Line Operations (cont.)

Options
-l Automatic line-end processing
-n Runs scrip for each input line like sed -n,
awk
-p Same as -n above but outputs result like sed
-v Prints version and patch level of Perl
-w Prints syntax warnings
Example options.pl
Sample execution perl -l011 options.pl tst.txt

9
Sample Perl Program

!/usr/bin/perl -w
print Enter a filename Prompt the user
sFile ltSTDINgt Wait for input
chop(sFile) Remove the newline
if (-e sFile) Test file existence
print sFile exists!\n
else
print sFile not found!\n
Example files.pl
Example chomp.pl

10
Basics

! Shebang
Comments
Statement termination
, -e Operators
ltSTDINgt Filehandles
sFile Variables
if Control structures
chop, print Functions

11
Review

Perl Language
How to Obtain Perl
Running a Perl Program
Command Line Operations
Sample Perl Program
Basics

12
Data Types and Contexts
13
Data Types

Scalars
nToday 3
print Today is asWeeknToday
Arrays of Scalars
_at_asWeek (Sun, Mon, Tue,
Wed, Thu, Fri, Sat)
Associative Arrays of Scalars (Hash)
hnWeek (Sun,0, Mon,1, Tue,2, Wed,
3,Thu,4, Fri,5, Sat,6)

14
Scalar Examples

nToday 3 Simple scalar assignment
asWeek3 Wed 4th element of array
hnWeekWed 3 One value from hash
nLast asWeek Last index of array
nTotal _at_asWeek Total count of array
Example
_at_asWeek (Sun, Mon, Tue, Wed, Thu,
Fri, Sat)
nLast asWeek nLast 6
nTotal _at_asWeek nTotal 7

15
Contexts

Scalar
nCount _at_asNames
List
_at_asNames (Larry, Moe, Curly)
Boolean
if (nCount gt nMax)
Void
1
Interpolative
print nCount nCount

16
Quoted Strings

Double Quoted
sStr1 nNbr1 nNbr1\n
Single Quoted
sStr1 nNbr1 nNbr1\n
Differences
Scalar Variable Interpolation
Backslash Character \
print nNbr1, \n Quotes not needed for
scalars.
print nNbr1\n More readable.

17
Escape Sequences

\n Newline
\r Carriage return
\t Horizontal tab
\f Form feed
\b Backspace
\a Alert (bell)
\e ESC character
\cC Control-C

18
Escape Sequences - Case

\u Next Character Uppercase
\l Next Character Lowercase
\U All Following Characters Uppercase
\L All Following Characters Lowercase
\Q Backslash All Non-AlphaNumeric
\E End \U, \L, or \Q

19
Escape Sequence Examples

Examples
sTxt lOWEr aND UpperCase
print(Uppercase \UsTxt\E\n)
print(Lowercase \LsTxt\E\n)
print(As a sentence \L\usTxt\E\n)
Output
Uppercase LOWER AND UPPERCASE
Lowercase lower and uppercase
As a sentence Lower and uppercase

20
Numeric Scalars

Integers Stored in Float Registers
Floating Point Values
.00045 45000
4.5e-4 4.5e4
Forcing Integer Interpretation
Block scope
use integer nNbr1 10 / 3
Single line
nNbr1 int 10 / 3 Truncates
Example numerics.pl

21
List Values

Separate individual values by commas
Usually enclosing the list in parentheses
Null list is represented by ()
List context a list is its values in order
_at_anTst (1, 2, 3) Initialize an array
Scalar context a list is the value of last
element
nTst (one, two, three) nTst is
three
Expression that return values may be in a list

22
Array Examples

Initialize an array
_at_anScores (95, 90, 92)
Assign scalar count and numeric array
nCount _at_anScores (95, 90, 92)
Slice of an array is named with _at_
_at_anSubArray _at_anScores1..2
Slice of a hash is named with _at_
_at_anDays _at_hnWeekMon, Wed, Fri
Example lists.pl
Example hashs.pl

23
Opening Closing Files

Syntax
open(FILEHANDLE, mode filename)
close(FILEHANDLE)
Modes
Read-only - file1 or ltfile1
Write-only - gtsFilename
Read/Write - ltfile1 or gt file1
Append-only - gtgtfile1
Read/Append - gtgt file1 ver. 5.004

24
Reading with ltgt

Reading from File
input ltMYFILEgt
Reading from Command Line
input ltgt
Reading from Standard Input
input ltgt
input ltSTDINgt
Example files.pl

25
Review

Data Types
Scalars Examples
Contexts
Quoted Strings
Numeric Scalars
List Values
Array Examples
File Handles

26
Statements
27
Simple Statements

Syntax
statement keyword condition
Keyword
if
unless
while
until
Example
print(Goodbye!\n) if sAns eq yes
Example compound.pl

28
Simple Statements (Cont.)

Example to Copy Files
!/usr/bin/perl
die(Unable to open input. !\n) unless
open(INFILE, infile)
die(Unable to open output. !\n) unless
open(OUTFILE, gtoutfile)
print(OUTFILE sLine) while
(sLine ltINFILEgt)
close(INFILE)
close(OUTFILE)
Example opens.pl

29
Compound Statements

Syntax
keyword (condition) statements
Example
if (sAns eq yes)
print(Goodbye!\n)

30
The if statement

Syntax
if (CONDITION) BODY
elsif (CONDITION) BODY
else BODY
Example
if (sDay eq Sun) nDay 0
elsif (sDay eq Mon) nDay 1
...
else print(Invalid day!\n)
Example tests.pl

31
The while statement

Syntax
while (CONDITION) BODY
Example
i 0 Initialize loop variable.
while (i lt 10) Test.
print(Iteration i\n)
i Increment.
Example whileloop.pl

32
The until statement

Syntax
until (CONDITION) BODY
Example
s Initialize loop var
until (s eq q) Test.
print(Enter word, q to quit )
chop(s ltSTDINgt) Change loop var
sLine . s

33
The for statement

Syntax
for (START STOP ACTION) BODY
Initially execute START statements once.
Repeatedly execute BODY until STOP is false.
Execute ACTION after each iteration.
Example
for (i0 ilt10 i)
print(Iteration i\n)
Example loops.pl

34
The foreach statement

Syntax
foreach SCALAR ( ARRAY ) BODY
Assign ARRAY element to SCALAR.
Execute BODY.
Repeat for each element in ARRAY.
Example
asTmp qw(One Two Three)
foreach s (_at_asTmp)s . sy
print(_at_asTmp) Onesy Twosy Threesy
Example foreach.pl

35
The do statement

Syntax
do BODY while CONDITION
do BODY until CONDITION
Example
do
sLine . s if s
print(Enter word, q to quit )
chop(s ltSTDINgt) Change loop var
until s eq q Test

36
Loop Control Statements

Last
Exit loop.
Next
Control passes to beginning of loop (executing
the for increment statement) to begin another
iteration.
Redo
Begin another loop iteration (bypass for
increment).
Continue
Used with while to avoid infinite loop when next
statement causes for increment to be bypassed.
Examples loopctrl.pl, split.pl

37
Review