Answer:

To generate UUID in PHP, you can try the script below:

<?php

function uuid($prefix = '') {
    $chars = md5(uniqid(mt_rand(), true));
    $uuid  = substr($chars,0,8) . '-';
    $uuid .= substr($chars,8,4) . '-';
    $uuid .= substr($chars,12,4) . '-';
    $uuid .= substr($chars,16,4) . '-';
    $uuid .= substr($chars,20,12);
    return $prefix . $uuid;
}

echo uuid();

It shows something like the following when executed:

c664b9b4-6c44-c8d9-acf9-93ef0e11e435

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Answer:

In GNU/Linux, there is a command that do nothing, unsuccessfully - the false command.

E.g.

# false

It is common to set the user shell to /bin/false if you don't want the user to login.

Reference: http://www.gnu.org/software/coreutils/manual/html_node/false-invocation.html

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Answer:

It is easy to clone an object in PHP, using the following method.

<?php

    $obj = new stdClass();
    $obj->foo = "foo";
    $obj->bar = "bar";

    $new_obj = clone $obj;
    var_dump ( new_obj );

It will print out...

object(stdClass)#2 (2) {
  ["foo"]=>
  string(3) "foo"
  ["bar"]=>
  string(3) "bar"
}

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Answer:

The Perl's grep function is very useful for list filtering.

E.g. Array filtering

my @new = grep {$_ > 1} (1,2,3);

# @new contains 2, 3 only

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Answer:

Most CentOS' mirrors don't host full mirror of Yum repository for all versions of CentOS. If you are using older version of CentOS, you might one-day found the yum update is broken since the mirror no longer contains the files you needed.

In this case, you can modify the file /etc/yum.repos.d/CentOS-Base.repo and change all paths point to the following:

..
baseurl=http://vault.centos.org/...
..

Then do a yum update to reflect the changes.

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Answer:

It is easy to create an array using the range() function, e.g.

<?php

foreach (range(0, 10) as $number) {
        echo $number, " ";
}

It shows following when executed:

0 1 2 3 4 5 6 7 8 9 10

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Answer:

Perl don't have try/catch statement by default, but you can simulate using the following way:

eval {
    print 1/0;
};

if ($@) {
    print "Error message: $@";
};

When executed, it shows:

Error message: Illegal division by zero at test.pl line 7.

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Answer:

Sometimes when you type the mysql command, it shows:

Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)

The cause of this problem is the MySQL socket file is not in the default location, e.g. /tmp/mysql.sock

To fix, edit the MySQL configurations, e.g. /etc/my.cnf, add the following lines

[client]
socket=/tmp/mysql.sock

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Answer:

Add a User in Linux, just use the useradd command:

# sudo useradd -d /home/john -m john

The above command will create the user john and create a home directory which is at /home/john

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Answer:

You might experience this error, especially when you are connecting to a remote Linux machine which has just got re-installed.

To solve this, enter the command:

# ssh-keygen -R 192.168.2.36

Where 192.168.2.36 is the IP you are connecting.

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