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PERL. By C. Shing ITEC Dept Radford University. Objectives. Understand the history Understand constants and variables Understand operators Understand control structures Understand functions Understand file I/O Understand command line arguments
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PERL By C. Shing ITEC Dept Radford University
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
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 • Print • Assignment • Conditional • Loop • Function (Subroutine)
Control Structures - Print • Syntax: each statement ends with ; Print variable [constant]; • Example: print "Please enter a number:";
Control Structures - Assignment • Syntax: each statement ends with ; Variable = expression Comment: begins with #
Control Structures - Assignment • Scalar Variable • Number: integer, real • Example: $i=5 $j=-6.2 • String: string, character • Example: $month=“January” $char=“\t”
Control Structures - Assignment • Scalar Variable • Number: integer, real • Example: $i=5; $j=-6.2; $number = <STDIN>; (keyboard input) • String: string, character • Example: $month=“January”; $char=“\t”; $guess = <STDIN>; (keyboard input) $fileString = <FILEHANDLE> (getting data from file)
Control Structures - Assignment • 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 • 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) $line =~ /(\w+)(\s+)(\w+)(\s+)/; (line that matches the pattern: word, spaces, word
Control Structures - Conditional • Syntax • If (condition) { } • If (condition) { } else { } • If (condition1) { } elsif (condition2) { } else { }
Control Structures - Conditional • Example: if ($guess eq "hello") { print "The word ".$guess." that you guessed is correct.\n\n"; }
Control Structures - Conditional • Example: if ($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 { $grade="F"; }
Control Structures - Loop • While • Until • Foreach • For
Control Structures – While Loop • Syntax while (condition) { } when condition is false, exit loop
Control Structures – While Loop • while ($line=<USERFILE>) { }
Control Structures – Until Loop • Syntax until (condition) { } when condition is true, exit loop
Control Structures – Until Loop • Example: until ($array2[0] eq "listing") { }
Control Structures – Foreach Loop • Syntax foreach variable (variableRange) { } when variable is outside of variableRange, exit loop
Control Structures – Foreach Loop • Example: foreach $month (1..12) { }
Control Structures – For Loop • Syntax for (initialization; condition; ending body stmt) { } when condition is false, exit loop
Control Structures – For Loop • Example: for ($i=1; $i<=12; ++$i) { }
Control Structures - Function (Subroutine) • Library function • User (-defined) function
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()
Control Structures – Library Function • Example: # search item through list foreach $user (@list) { if ($user eq lc($item)) { $user_correct = 1; } } # foreach
Control Structures – Library Function • keys(): gives the key value of the hash • chomp(): delete the new line character from variable • split (delimiter, variable) : split a variable using delimiter • my(): create local variable • shift (arrayName): get rid of 1st element in the arrayName • push (array1, array2): push array2 to the end of array1
Control Structures – Library Function • Example: while ($line=<NAMEFILE>) { chomp($line); # username are separated by space(s) @array=split /\s+/, $line; }
Control Structures – Library Function • 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 • Open/Close file: • Syntax: open (FILEHANDLE, “<filename”); close (FILEHANDLE);
File I/O • 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
