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Perl Snippets

This is a collection of Perl snippets I've written or otherwise come across that I would like available for future reference.

Prints contents of a file

sub showFileContents {
    my $file = $_[0];
    open FILE, "<$file";
    my @hold = <FILE>;
    foreach(@hold) {
        print $_;
    }
    close FILE;
}

clears screen and then prints provided string

sub printHeader {
    my $header = $_[0];
    runOnSystem("clear");
    print "\n\n\t$header:\n\n";
}

executes system command and communicates to user what it's doing - be sure to be careful of arbitrary code execution

sub runOnSystem {
    my $command = $_[0];
    my $debug = $_[1];
    if ($debug) {
        print "debug: $command\n";
    } else {
        print "\n\n[[executing: $command]]\n\n";
        system("$command");
    }
}

prompts user to press enter to continue

sub enterToContinue {
    print "\nPress enter to continue...\n";
    my $enter = <STDIN>;
}

provided a prompt, will ask user how to proceed, assuming YES and else opting no

sub checkYn {
    my $prompt = $_[0] . " [Y/n]:";
    print "$prompt";
    my $rVal = -1;
    while($rVal == -1) {
        chomp(my $yn = <STDIN>);
        if ($yn =~ /^y*$/i) {
            $rVal = 1;
        } elsif ($yn =~ /^n+$/i) {
            $rVal = 0;
        } else {
            print "Sorry, that's not valid input. Please try again:\n\n$prompt";
        }
    }
    return $rVal;
}

provided a prompt, will ask user how to proceed, assuming NO and else opting yes

sub checkyN {
    my $prompt = $_[0] . " [y/N]:";
    print "$prompt";
    my $rVal = -1;
    while($rVal == -1) {
        chomp(my $yn = <STDIN>);
        if ($yn =~ /^y+$/i) {
            $rVal = 1;
        } elsif ($yn =~ /^n*$/i) {
            $rVal = 0;
        } else {
            print "Sorry, that's not valid input. Please try again:\n\n$prompt";
        }
    }
    return $rVal;
}

asks for user input, then returns the input with optional sanitization

sub userInput {
    my $prompt = $_[0] . ":";
    print "$prompt";
    my $rVal;
    while(!defined $rVal) {
        chomp(my $userTyped = <STDIN>);
        $rVal = sanitizeUserInput($userTyped);
        if (!defined $rVal) {
            print "Sorry, that's not valid input. Please try again:\n\n$prompt";
        }
    }
    return $rVal;
}

sub sanitizeUserInput {
    my ($userTyped) = @_;
    ## process $userTyped here - return undef if new input is required;
    chomp($userTyped);
    if ((length $userTyped) == 0) {
                    undef $userTyped;
    }
    return $userTyped;
}

gets the directory of the currently running script. note requirement

sub getExecutableDirectory {
    ## requires use Cwd 'abs_path';
    my $fullPath = abs_path($0);
    my $dirname  = dirname($fullPath);
    return $dirname;
}

template for getting a timestamp string

sub getTimeStampString() {
    ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime(time);

    $year += 1900;
    $mon += 1;
    $mon = sprintf("%02d", $mon);
    $mday = sprintf("%02d", $mday);
    $hour = sprintf("%02d", $hour);
    $min = sprintf("%02d", $min);
    $string = "$year$mon$mday-$hour$min";
    return $string;
}

process arguments provided from command line

this one is a bit more specific, but should be easily adaptable

sub processArguments {
    $ranSomething = 0;
    for (my $i = 0; $i < scalar(@ARGV); $i++) {
        my $arg = $ARGV[$i];
        if ($arg =~ /^-(\w)/) {
            $arg = $1;
            processArgument($arg, $ARGV[$i + 1]);
        }
    }
    if ($ranSomething == 0) {
        print "Usage: example usage\n";
    }

}
sub processArgument {
    my $arg = $_[0];
    my $nextArg = $_[1];
    if ($arg eq "c" && $nextArg ne "") { #maybe do -e
        # most of these are examples as to how to use this code
        # my $confFile = $nextArg;
        # loadConfFile($confFile);
    } elsif ($arg eq "d") {
        #$debug = 1;
    }
}

check for a trailing slash in a string

sub checkTrailingSlash {
    my $str = $_[0];
    if ($str !~ /\/$/) {
        $str .= "/";
    }
    return $str;
}

this document last modified: February 03 2018 16:50

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