Perl: remove empty elements from array

I have an array with a bunch of empty strings, and other "empty" items, that I want to remove. Perl's grep() command makes this very simple:

@a = ("one", "", "three", "four", 0, "", "\n", "eight")

@a = grep($_, @a);

The first argument to grep is an expression which evaluates whether $_ is true (ie. a truthy value). This could easily also have been $_ ne "" so we don't also filter out false and 0.

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Perl: assign a regexp search/replace to a variable

Often I will want to assign a variable to be a search and replace of another variable. Logically you might write it like this:

$str = "foofoofoobar";
$new = $str =~ s/foo/FOO/g;

# $new contains 3 because three things were replaced in the string
print "$new\n";

This will not work because you are assigning the number of replacements made to $new. This is not what we wanted. Instead we want the search and replace to return the new string:

$str = "foobar";
$new = $str =~ s/foo/FOO/gr;

print "$new\n";

Note the /r after the regular expression. Documentation on /r is in Perlop

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Reddit: School funding

It's not about priorities. It's about budget allocation and constraints. There is a common misunderstanding between many governmental systems, charities, and other non-profit organizations.

The public tends to think that their school has X amount of money and that money is in one big pile that they can spend on anything. The public assumes that teachers, overhead, and operating costs should get paid first, then schools can buy fancy new computers, renovate buiildings, etc...

Unfortunately, that's not how budgets work 99% of the time. School districts often receive large gifts and grants from individuals and organizations that they are contractually obligated to spend on certain goals/objects. Joe Schmo didn't give Y school district $1,000,000 to spend on anything; he gave them $1,000,000 under the conditions that the money is spent on school equipment for the kids (i.e. laptops, desktops, textbooks, playground equipment, etc...). He can exclude or include any specific item or place for the funds to be used. School districts occasionally have local taxes levied for them. For example, my area (about three school districts) imposes a 1% additional sales tax on its citizens. The 1% collected HAS to be used on school renovations, period. The money cannot be used for anything else. In a similar manner, one of the three school districts is putting to vote a tax that would raise property assessment tax by $0.20/$1,000. That money HAS TO BE spent on upgrading school playground equipment, and the school has outlined a 7+ year plan of fund implementation for specific schools within the district.

Borrowed from MisfitMonk on Reddit

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Coreutils Viewer

I just found Coreutils Viewer, which gives you a progress meter for Linux coreutils. Specifically it can give status on cp, mv, dd, tar, gzip, and cat. It's great for doing a big dd to a flash drive or SD card.

I've used it with good success on Raspberry Pi SD card images.

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PHP: is_ip() to test if a string is a valid IP address

I needed to test if a string was a valid IP address or not. PHP has filter_var() which tests for a lot of common things (email addresses, urls, etc) but I can never remember the syntax. Here is a simple wrapper function to match IPv4 and IPv6 addresses.

function is_ip($str) {
    $ret = filter_var($str, FILTER_VALIDATE_IP);

    return $ret;
}

If you just want to match IPv4 addresses:

function is_ipv4($str) {
    $ret = filter_var($str, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4);

    return $ret;
}
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PHP: fakepath() to clean up a file path

Needed a quick function to remove relative elements from a path. Similar to PHP's realpath() but doesn't require the file to exist on the local filesystem. This also works for URLs.

function fakepath($url) {
    $split = preg_split("|/|",$url);
    $first = substr($url,0,1);

    foreach ($split as $item) {
        if ($item === "." || $item === "") {
            // If it's a ./ then it's nothing (just that dir) so don't add/delete anything
        } elseif ($item === "..") {
            // Remove the last item added since .. negates it.
            $removed = array_pop($ret);
        } else {
            $ret[] = $item;
        }
    }

    // Rebuild the string
    $ret = join("/",$ret);

    // Remove dupe /
    $ret = preg_replace("!/+!","/",$ret);

    // Restore the double / after the HTTP:
    $ret = preg_replace("!(https?:/)!","$1/",$ret);

    if ($first === '/') {
        $ret = "/$ret";
    }

    return $ret;
}
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CentOS 7 has been released

CentOS 7.0 has been released and I gathered the versions of some core packages:

Package Version
Perl 5.16.3
PHP 5.4.16
Vim 7.4.160
Firefox 24.6.0
Apache 2.4.6
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PHP: Assign a default value to a variable

PHP E_ALL causes a warning to be thrown if you read an unitialized value from an array. For example if you did $debug = $_GET['debug']; but debug is not present in $_GET.

This function will conditionally assign a value to a variable that will not cause a warning to be thrown. It also has the added benefit of having a default option that you can specify.

function var_set(&$value, $default = null) {
    if (isset($value)) {
        return $value;
    } else {
        return $default;
    }
}

This allows us to safely assign a variable from the superglobals.

# Default of null if not in array
$debug = var_set($_GET['debug']);

# Specific default of 99
$level = var_set($_GET['level'],99);
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PHP: is_flat_array()

PHP supports numeric and associative arrays. PHP's numeric arrays do not have to be sequential, and I wanted a test for that.

function is_flat_array($array) {
    if (!is_array($array)) { return false; }

    $current = 0;
    foreach (array_keys($array) as $key) {
        if ($key !== $current) { return false; }

        $current++;
    }

    return true;
}

I wrote up all the test cases I could think of:

var_dump(is_flat_array(array(1, 2, 3)));                // True
var_dump(is_flat_array(array()));                       // True
var_dump(is_flat_array(array('foo' => 'bar')));         // False
var_dump(is_flat_array(array(0 => 3, 'foo' => 'bar'))); // False
var_dump(is_flat_array(array(0 => 3, 1 => 3, 2 => 3))); // True
var_dump(is_flat_array(array(0 => 3, 2 => 3, 3 => 3))); // False
var_dump(is_flat_array("foo"));                         // False

See also: Test for numeric and associative arrays

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NASA Radio - Third Rock Radio

NASA has a cool online radio station called Third Rock Radio. They play an eclectic mix of music and space related tidbits.

Third Rock Radio ShoutCast Stream suitable for VLC.

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FFMpeg: Encode a VP9 .webm video

I needed to convert an .mp4 file to a VP9 .webm file. FFMpeg defaults to using VP8 for .webm files, but VP9 is broadly supported by both Firefox and Chrome now so I'd rather use that.

Uses the default, and makes a VP8 files:

ffmpeg -y -i input.mp4 /tmp/output.webm

Force the codec to be VP9:

ffmpeg -y -i input.mp4 -codec:video vp9 /tmp/output.webm
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Perl: Using modules and @INC

I was going to write an article about using modules in Perl but Perl Maven did a better job than I ever could have. The article explains all the places Perl looks to find a given module, and how you give it alternate locations. The only thing I would add is that if you print out %INC it will list all the modules that were loaded, and from where.

use Data::Dumper;

print Dumper(\%INC);

Outputs:

$VAR1 = {
          'strict.pm' => '/usr/share/perl5/strict.pm',
          'Data/Dumper.pm' => '/usr/lib64/perl5/vendor_perl/Data/Dumper.pm',
          'warnings/register.pm' => '/usr/share/perl5/warnings/register.pm',
          'vars.pm' => '/usr/share/perl5/vars.pm',
          'overloading.pm' => '/usr/share/perl5/overloading.pm',
          'Carp.pm' => '/usr/share/perl5/vendor_perl/Carp.pm',
          'overload.pm' => '/usr/share/perl5/overload.pm',
          'constant.pm' => '/usr/share/perl5/vendor_perl/constant.pm',
          'bytes.pm' => '/usr/share/perl5/bytes.pm',
          'warnings.pm' => '/usr/share/perl5/warnings.pm',
          'XSLoader.pm' => '/usr/share/perl5/XSLoader.pm',
          'Exporter.pm' => '/usr/share/perl5/vendor_perl/Exporter.pm'
        };

Looks like Data::Dumper has quite a few dependencies.

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MySQL: Reset the auto increment counter

In MySQL if you need to reset the AUTO_INCREMENT counter (i.e. After you did a bunch of deletes) you can run the following command:

ALTER TABLE MyTable AUTO_INCREMENT = 924;

This will cause 924 to be the next number given out for your AUTO_INCREMENT column.

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Fonts: Comic Neue aka "good" Comic Sans

Comic Sans has long been the whipping boy of bad fonts. There are many other good casual sans-serif fonts available, but Comic Neue is a great free alternative. If you must use a casual font, at least use a good one.

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Javascript: Random element from array

Function to get a random element from a Javascript array.

function rand_elem(items) {
    var item = items[Math.floor(Math.random() * items.length)];

    return item;
}
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