Transcript Chapter 1 What is Unix?

PERL
By C. Shing
ITEC Dept
Radford University
Objectives
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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
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
Constants
• Scalar:
– Number: integer, real, scientific notation
– String: within “ “
• Boolean:
– 1 represents true
– 0 represents false
Variables
• Scalar: begin with $
– Number: integer, real
– String: string, character
• Array: begin with @
– Index starts from 0
• Associative: begin with %
– use hash
Control Structures
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Print
Assignment
Conditional
Loop
Function (Subroutine)
Control Structures - Print
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Syntax: each statement ends with ;
Print variable [constant];
– Example:
print "Please enter a number:";
Control Structures - Assignment
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Syntax: each statement ends with ;
Variable = expression
Comment: begins with #
Control Structures - Assignment
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Scalar Variable
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Number: integer, real
– Example:
$i=5
$j=-6.2
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String: string, character
– Example:
$month=“January”
$char=“\t”
Control Structures - Assignment
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Scalar Variable
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Number: integer, real
– Example:
$i=5;
$j=-6.2;
$number = <STDIN>; (keyboard input)
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String: string, character
– Example:
$month=“January”;
$char=“\t”;
$guess = <STDIN>; (keyboard input)
$fileString = <FILEHANDLE> (getting data from file)
Control Structures - Assignment
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Array Variable
– Example:
@array = ("john", "susan", "david", "sarah", "ryan",
"laura");
@numRange = (1..6);
Where
$array[0] = “john”;
$array[1] = “susan”;
$array[5] = “laura”;
Control Structures - Assignment
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Associative Variable
– Example:
%hash = ("smith"=>"john", "sides"=> "susan",
"davis"=>"david", "star"=>"sarah",
"rush"=>"ryan","lane"=> "laura");
Where
$array{“smith”} = “john”;
$array{“sides”} = “susan”;
$array{“lane”} = “laura”;
Operators – Arithmetic, Logic,
Relational
• Arithmetic: +,-,*,/
• Logical: &&, ||
• Relational
– Numeric: ==, !=, >, >=, <, <=
– String: eq, ne, gt, ge, lt, le
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)
$line =~ /(\w+)(\s+)(\w+)(\s+)/; (line that matches the
pattern: word, spaces, word
Control Structures - Conditional
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Syntax
1. If (condition)
{
}
2. If (condition) {
else
{
}
3. If (condition1) {
elsif (condition2)
{
}
else
{
}
}
}
Control Structures - Conditional
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Example:
if ($guess eq "hello")
{
print "The word ".$guess." that you
guessed is correct.\n\n";
}
Control Structures - Conditional
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Example:
if ($avg >=0.895*$avgall)
{
$grade="A";
}
elsif ($avg >=0.795*$avgall)
{
$grade="B";
}
elsif ($avg >=0.695*$avgall)
{
$grade="C";
}
elsif ($avg >=0.595*$avgall)
{
$grade="D";
}
else
{
$grade="F";
}
Control Structures - Loop
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3.
4.
While
Until
Foreach
For
Control Structures – While Loop
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Syntax
while (condition)
{
}
when condition is false, exit loop
Control Structures – While Loop
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while ($line=<USERFILE>)
{
}
Control Structures – Until Loop
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Syntax
until (condition)
{
}
when condition is true, exit loop
Control Structures – Until Loop
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Example:
until ($array2[0] eq "listing")
{
}
Control Structures – Foreach Loop
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Syntax
foreach variable (variableRange)
{
}
when variable is outside of
variableRange, exit loop
Control Structures – Foreach Loop
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Example:
foreach $month (1..12)
{
}
Control Structures – For Loop
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Syntax
for (initialization; condition; ending body
stmt)
{
}
when condition is false, exit loop
Control Structures – For Loop
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Example:
for ($i=1; $i<=12; ++$i)
{
}
Control Structures - Function
(Subroutine)
1. Library function
2. User (-defined) function
Control Structures – Library
Function
1. lc() or lc : convert to lower case
2. uc(): convert to upper case
3. open(), close(), die(), exit(), last(): See
File I/O
4. print()
5. length(): length of string
6. index()
Control Structures – Library
Function
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Example:
# search item through list
foreach $user (@list)
{
if ($user eq lc($item))
{
$user_correct = 1;
}
} # foreach
Control Structures – Library
Function
7. keys(): gives the key value of the hash
8. chomp(): delete the new line character
from variable
9. split (delimiter, variable) : split a variable
using delimiter
10. my(): create local variable
11. shift (arrayName): get rid of 1st element
in the arrayName
12. push (array1, array2): push array2 to the
end of array1
Control Structures – Library
Function
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Example:
while ($line=<NAMEFILE>)
{
chomp($line);
# username are separated by space(s)
@array=split /\s+/, $line;
}
Control Structures – Library
Function
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Example:
foreach $userkey (keys %hash)
{
if ($hash{$userkey} eq lc($name))
{
$user_correct = 1;
$lastname=$userkey;
}
} # foreach
Control Structures – User Function
• Function call:
– Syntax:
functionname (actualParameterList);
– Example:
check ($name, @array);
Control Structures – User Function
• Function definition:
– Syntax:
sub functionname
{
my $localVar1 = $_[0];
my $localVar2 = $_[1];
my @localArray = @_;
}
Control Structures – User Function
• Function definition:
– Example:
check ($name, @array);
sub check
{
# the following 3 lines declare local variables
my $item = $_[0];
my @list = @_;
my $user_correct = 0;
}
Control Structures – User Function
• Example:
printArray(@array);
sub printArray
{
# @array is a local variable in the sub
my @array = @_;
foreach $cell (@array)
{
print $cell."\t";
}
print "\n";
} # sub printArray
File I/O
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Open/Close file:
– Syntax:
open (FILEHANDLE, “<filename”);
close (FILEHANDLE);
File I/O
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Open/Close file:
– Example:
# read all names into @array from input data file:
sixth2.txt
open (NAMEFILE, "<sixth2.txt")
|| die "Error: Unable to open the file $!";
# open output file for print
open (OUTFILE,">attend.txt");
print OUTFILE "Lastname\t\tFirstname\t\tE-Mail
Name\n";
Command Line Arguments
• perl –w filename.pl arg0 arg1 arg2 …
• Arg0, arg1 and arg2… are command line
arguments
• Inside the program, they are stored in
array @ARGV
Command Line Arguments
• Example:
open (USERFILE, "<user$ARGV[0].txt") || die
"Error: Unable to open the file $!";
open (OUTFILE,">attend$ARGV[0].txt");
print OUTFILE "Library Attendance for ITEC
100-$ARGV[0]\n\n";
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
System Administration
• Example: Run Perl in Unix environment
– system("/usr/local/gnu/bin/awk '{print
\$1,\$2,\$9}' temp1.txt > 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");
Reference
• Some simple examples