$re = '/
(?:\n|\A)[ ]*
# 1: Opening marker
(
[ ]{0,2}(?:~{3,}|`{3,}) # 3 or more tildes/backticks.
)
[ ]*
(?:
\.?([\w-_:\.\/\{\+\},\@]+) # 2: standalone class name
|
\{((?:[ ]*[#.][-_:a-zA-Z0-9]+){1,})[ ]*\} # 3: Extra attributes
)?
[ ]* \n # Whitespace and newline following marker.
# 4: Content
(
(?>
(?!\1 [ ]* \n) # Not a closing marker.
.*\n+
)+
)
# Closing marker.
\1 [ ]* (?= \n )/mx';
$str = '
B1B
{{ site.data.reusables.ssh.dsa-support }}
{{ site.data.reusables.command_line.open_the_multi_os_terminal }}
2. Enter `ls -al ~/.ssh` to see if existing SSH keys are present:
```shell
$ ls -al ~/.ssh
# Lists the files in your .ssh directory, if they exist
```
dadas
dasdasdasda
~~~dadasd
$ ls -al ~/.ssh
# Lists the files in your .ssh directory, if they exist
~~~
3. Check the directory listing to see if you already have a public SSH key.
By default, the filenames of the public keys are one of the following:
* *id_dsa.pub*
* *id_ecdsa.pub*
* *id_ed25519.pub*
* *id_rsa.pub*
- If you don\'t have an existing public and private key pair, or don\'t wish to use any that are available to connect to GitHub, then [generate a new SSH key](/articles/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent).
- If you see an existing public and private key pair listed (for example *id_rsa.pub* and *id_rsa*) that you would like to use to connect to GitHub, you can [add your SSH key to the ssh-agent](/articles/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent/#adding-your-ssh-key-to-the-ssh-agent).
{{#tip}}
**Tip:** If you receive an error that *~/.ssh* doesn\'t exist, don\'t worry! We\'ll create it when we [generate a new SSH key](/articles/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent).
{{/tip}}';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php