Variable Types

Perl Variable Types Table

Variable Examples

# Assign an array of weekdays:
@weekdays = ("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday");
print @weekdays;

# Find size of the array:
$arraysize = scalar(@weekdays);

# C style For Loop and print statments to print array elements and index
# (this is not the only For Loop style in Perl):
for($i = 0; $i < $arraysize; $i ++) {
   printf("\n%d: @weekdays[$i]", $i);
}
printf("\n\n");

# Another For Loop syntax for Perl,
# this adds a last statement to limit the iterations:
foreach my $j (0..($arraysize-1)) {
   print "\n$j: @weekdays[$j]";
   last if ($j > 3);
}
print "\n\n";

# Sets $day to Wednesday from the @weekdays array:
$day = $weekdays[2];
print "$day\n";

# Assign a hash of months:
%months1 = ("First", "January", "Second", "February", "Third", "March", "Fourth", "April", "Fifth", "May", "Sixth", "June", "Seventh", "July", "Eighth", "August", "Ninth", "September", "Tenth", "October", "Eleventh", "November", "Twelfth", "December");


# Sets $m1 to September from the %months1 hash:
$m1 = $months1{"Ninth"};
print "\n$m1\n\n";

# Or you can assign the same hash as follows:
%months2 = (
    "First" => "January",
    "Second" => "February",
    "Third" => "March",
    "Fourth" => "April",
    "Fifth" => "May",
    "Sixth" => "June",
    "Seventh" => "July",
    "Eighth" => "August",
    "Ninth" => "September",
    "Tenth" => "October",
    "Eleventh" => "November",
    "Twelfth" => "December",
);

# Sets $m2 to September from the %months2 hash:
$m2 = $months2{"Ninth"};
print "$m2\n\n";

# Find the keys and values of the %months2 hash,
# and print them:
@vals = values %months2;
@keys = keys %months2;
print "\nValues: @vals\n";
print "\nKeys: @keys\n";

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Match & Replace Optional Modifiers

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Perl Basic Metacharacters

The Perl Metacharacters, which are used in the "pattern" section of the m/pattern/ and s/pattern/replacement/ operators, involve the following characters:

+ ? . * ^ $ ( ) [ { | \

Patterns are interpolated as double quoted strings. The standard string escapes have their usual interpolated meanings except for \b, which matches word boundries. Although in a character class, \b goes back to matching a backspace.

Basic Perl Metacharaters Used In Search/Replace Patterns

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Perl Special Metacharacters

The special meaning of non-alphanumeric characters can be escaped with a \. However, most alphanumeric characters gain a specail meaning with the \.

Special Perl Metacharaters Used In Search/Replace Patterns

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Standard Perl Charater Class Metasymbols

Metasymbol/Character Class Equivalence Table

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Perl Special Variables

Perl Special Variables Table (This Is Not A Complete List)

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General Examples

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# Open an existing file named file.txt, and assign the filehandle TEXTFILE:
open(TEXTFILE, "file.txt") or die "Cannot open file: $!\n";

# Open an existing file named file.txt, explicit form:
open(TEXTFILE, "<file.txt") or die "Cannot open file: $!\n";

# Create a file named file.txt:
open(TEXTFILE, ">file.txt") or die "Cannot open file: $!\n";

# Append to an existing file named file.txt:
open(TEXTFILE, ">>file.txt") or die "Cannot open file: $!\n";


# Read the file line-by-line to the end; the line is saved to $line:
while ($line = <TEXTFILE>) {
    ...
    ...
    ...
}

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#!/usr/bin/env perl

use strict;
use warnings;

=head1 Description

T. Hawkins, Basic File I/O

Tested using Srawberry Perl for Windows

This Perl script is run on the command line with
the following arguments separated by a space:

$file_old: existing file that contains lines of text.

$file_new: new file that will be created.

$donotprint: if the old files has this full word, then
that line will not be printed in the new file, otherwise,
all lines will be printed in the new file.

There must be 1 or more white spaces after the search
word entered ( 3rd command line argument, or the
$donotprint string variable) that will be seached in
"non-greedy" mode, or as few white space seaches as
possible: \s+?

The overall match search will be performed only once with
the m//o operator.

There can be any number alphanumeric characters or white
spaces in front of the search string. the @- Perl
variable will show the offset of the point at which the
seach was successful.

=cut

my($file_old, $file_new, $donotprint) = @ARGV;

die "$file_old name must have at least three chars, $!" if length($file_old) < 3;
die "$file_new name must have at least three chars, $!" if length($file_new) < 3;

open (IN, "<$file_old") or die "Can't open $file_old, $!";
open (OUT, ">$file_new") or die "Can't open $file_new, $!";

while(my $line = <IN>) {
    if($line !~ m/$donotprint\s+?/o) {
        print "At Line Number $.: $line";
        print OUT "$line";
    }
    else {
        print "At Line Number $.: Won't print to new file->\"$donotprint\" Match Offset: @-\n"
    }
}

close IN;
close OUT;

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#!/usr/bin/env perl

use strict;
use warnings;

=head1 Description

T. Hawkins, Basic Method Calling

Tested using Srawberry Perl for Windows

This Perl script is run on the command line with words
followed, separated by a space:

Each word will print after the word "Hello."

=cut

&hello_sub ( @ARGV );

sub hello_sub {

    my $name = shift @_;

    print "Hello, $name\n";
    while ( @_ ) {
        $name = shift @_;
        print "Hello again, $name\n";
    }
}

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#!/usr/bin/env perl

use strict;
use warnings;

=head1 Description

T. Hawkins, Log File Rearrangement & Manipulation

There is a log file of data from operation of a system that
has the following data:

Index Channel Power Impedance Voltage Current

1   A   0.00     0       0.06   0.000
2   B   0.307   258   8.90   0.034
3   C   0.271   302   9.07   0.030
4   D   0.242   345   9.18   0.027
5   A   0.381   204   8.82   0.043
6   B   0.344   253   9.33   0.037
7   C   0.296   300   9.45   0.031
8   D   0.260   345   9.52   0.028
...
...
... Many more lines ...

The desire is to extract only the Impedance, Voltage,
and Current data from Channel A, and put it into a comma
delimitted format so it can be graphed for characterization.

The input file contains the results of a stream of data
with values separated by white spaces.

The split(/\s+/, $line) function is used on each line of the
input file to put the fields into the @strings array. The
fields are separated by any number of white spaces.

The individual @string array values are manipulated and
printed to the terminal.

The following sytax keeps the "Use of uninitialized value
in string eq" warning from occuring:
$value = defined($strings[1]) ? $strings[1] : "";

=cut

my $file_in = $ARGV[0];

die "$file_in must have at least three chars, $!" if length($file_in) < 3;

open (IN, "<$file_in") or die "Can't open $file_in, $!";

my @strings;

print"$file_in\n";
print"Impedance,Voltage, Current\n";

while(my $line = <IN>) {
    @strings = split(/\s+/, $line);
    my $value = defined($strings[1]) ? $strings[1] : "";
    if($value eq "A"){
        print "$strings[3],$strings[4],$strings[5]\n";
    }
}

close IN;

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##################################################
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#!/usr/bin/env perl

use strict;
use warnings;

=head1 Description

T. Hawkins, Log File Rearrangement & Manipulation

There is a log file of generated data that
has the following form:

40000000
29CD9578
FFFFFFFFF69BF7CA
FFFFFFFFC9EDEB51
FFFFFFFFC2C17D53
FFFFFFFFE61086BD
1B5D100A
3DAE81CF
3536CC52
07D59396
FFFFFFFFD5052D98
FFFFFFFFC004EF40
FFFFFFFFD76619B7
...
...
... many more lines ...

The data consists of 2's complement numbers in Hex format
generated by a 64 bit computer. It can be seen that the
negative numbers have a series of leading hex F's, i.e, the
higest bit is a one.

The data must be used on a 32 bit hardware platform, so the
total number of hex digits representing each number must be
8. There is not a problem with the positive numbers because
the highest positive number fits within 8 hex digits.
However, the negative numbers of this very long file need to be
adjusted.

This Perl script reads in the file given as a parameter in the
command line. It searches each line and matches 8 characters
from the end of the line with:
$line =~ m/.{8}$/g

The search result is then taken from the Perl specail variable with:
$string = $&;

It then prints each line matched to the terminal.

=cut

my $file_in = $ARGV[0];

die "$file_in must have at least three chars, $!" if length($file_in) < 3;

open (IN, "<$file_in") or die "Can't open $file_in, $!";

my $string;

while(my $line = <IN>) {
    $line =~ m/.{8}$/g;
    $string = $&;
    print "$&\n";
}

close IN;

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References

(1) Perl.org

(2) perl.plover.com

(3) Strawberry Perl

(4) Active Perl

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