Chapter 17
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#!/usr/bin/perl -w
# Classic “Hello World” as done with Perl
print “Hello World!\n”;

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#!/usr/bin/perl -w
# Create a file that will have a directory listing of user’s home dir
print “About to read user’s home directory\n”;
# open the home directory and read it
opendir(HOMEDIR, “.”);
@ls = readdir HOMEDIR;
closedir(HOMEDIR);
print “About to create file dirlist.txt with a directory listing of user’s
home dir\n”;
# open a file and write the directory listing to the file
open(FILE, “>dirlist.txt”);
foreach $item (@ls) {
print FILE $item .”\n”;
}
close(FILE);
print “All done\n\n”;
}

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# Global variable $name is given a name
$name = Paul
# Enter our loop
foreach (@filedata) {
# declare a new variable for just the loop
my $current_file_file;
# create a local version of name to temporarily assign values within the
# loop to
local $name
...
}

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while ( $counter < 10 ) {
print $counter . “\n”;
$counter++;
}

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do {
print $counter . “\n”;
$counter++;
} while ( $counter < 10);

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foreach $temp (@authors) {
print $temp . “\n”;
}

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if ( $name eq ‘Paul’ ) {
print “Hi Paul\n”;
} elsif ($name eq ‘Joe’) (
print “Hi Joe\n”;
} elsif ($name eq ‘Jeremy’) {
print “Hi Jeremy\n”;
} else {
print “Sorry, have we meet before? “;
}

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#!/usr/bin/perl -T
# check.pl
# A Perl script that checks the input to determine if
# it contains numeric information
# First set up your Perl environment and import some useful Perl packages
use warnings;
use diagnostics;
use strict;
my $result;
# Next check for any input and then call the proper subroutine
# based on the test
if (@ARGV) {
# If the test condition for data from standard in is true run
# the test subroutine on the input data
$result = &test;
} else {
# else the test condition is false and you should run an error routine.
&error;
}
# Now print the results
print $ARGV[0].” has “.$result.” elements\n\n”;
exit (0);
sub test {
# Get the first array element from the global array ARVG
# assign it to a local scalar and then test the local variable
# with a regular expression
my $cmd_arg = $ARGV[0];
if($cmd_arg =~ m/[0-9]/) {
return (‘numeric’);
} else {
# There was a error in the input; generate an error message
warn “Unknown input”;
}
}
sub error {
# There was no input; generate an error message and quit
die “Usage: check.pl, (<INPUT TO CHECK>)”;
}

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