Cody Taylor

If you spend a lot of time on the linux command line you quickly find that it requires a lot of typing and retyping commands. I used to find myself using the exact same lengthy command multiple times a day and to get there I would type “history | grep some_command” and then execute it from there. Since I knew enough to get the job done I hadn’t really tried to find more efficient ways of doing the same old thing. But when I found out about the Linux bang (!) commands I realized how wasteful what I was doing really was.

The exclamation mark, in this case, is referred to as a ‘bang’.

• !!
  This bang command, when entered into the bash shell will run the previous command. It basically does the same thing as hitting the up arrow to take you to the previous command and then hitting enter.
   
• !ls
  This will run the last command that started with ‘ls’. If you ran ‘ls -al /etc/init.d’ a few commands ago and then you type ‘!ls’ the full command will be run again, assuming that you haven’t used that command since then.
   
• !ls:p
  This will display the command instead of running it.
   
• !$
  This one will run the last word of the previous command. This one is mainly useful for substitutions.
   
• !$:p
  Instead of running the last word of the previous command this will print it out.
   
• !*
  This bang command will run the previous command without the first word. This one is also only really useful for substitutions as we see in the examples that follow.
   
• !*:p
  This will print the previous command without the first word.
   

Here are a few examples of how to use these bash bang commands in everyday command line usage :

For the purposes of these examples, every example will assume these are the last three commands you ran:

    % which firefox
    % make
    % ./foo -f foo.conf
    % vi foo.c bar.c

Getting stuff from the last command:

    Full line:     % !!            becomes:   % vi foo.c bar.c
    Last arg :     % svn ci !$     becomes:   % svn ci bar.c
    All args :     % svn ci !*     becomes:   % svn ci foo.c bar.c
    First arg:     % svn ci !!:1   becomes:   % svn ci foo.c

Accessing commandlines by pattern:

    Full line:     % !./f          becomes:   % ./foo -f foo.conf
    Full line:     % vi `!whi`     becomes:   % vi `which firefox`
    Last arg :     % vi !./f:$     becomes:   % vi foo.conf
    All args :     % ./bar !./f:*  becomes:   % ./bar -f foo.conf
    First arg:     % svn ci !vi:1  becomes:   % svn ci foo.c

I found those examples here.

Everyone seems to be all about Twitter so here’s some simple examples of how to update your Twitter status from a command line prompt, web server or simple html web site. These three examples require curl so install it if you don’t already have it. For these examples I’ll be using my Twitter user name ‘codytaylor1234’. My password is not ‘mypassword’ so make sure you put in your own information.

The easiest way to update your Twitter account is to just call curl from the command line with this command.

curl --basic --user "codytaylor1234:mypassword" --data-ascii 
"status=This Twitter update brought to you by curl on the command line" 
"http://twitter.com/statuses/update.json"

To update your Twitter status with PHP you are going to want to do the same sort of thing but with a bit more typing.

<?php
$username = 'codytaylor1234';
$password = 'mypassword';

$update = 'This Twitter update is from a php script using curl';

$url = 'http://twitter.com/statuses/update.json';

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "$url");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, "status=".$update);
curl_setopt($ch, CURLOPT_USERPWD, $username.":".$password);
$result = curl_exec($ch);
curl_close($ch);

if($result)
    echo 'success';

?>;

Since a cross-domain request in Javascript isn’t really an option we have to create a proxy using PHP in order to authenticate the user on the Twitter API. If anyone knows an easy way authenticate a Twitter user using only javascript I’d love to hear it. Anyway if we replace a small amount of code in the above example and put it in a file then we can use a simple ajax request to update our Twitter status. So the new PHP file would be:

<?php
$username = $_POST['username'];
$password = $_POST['password'];

$update = $_POST['update'];

$url = 'http://twitter.com/statuses/update.json';

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "$url");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, "status=".$update);
curl_setopt($ch, CURLOPT_USERPWD, $username.":".$password);
$result = curl_exec($ch);
curl_close($ch);

?>

For this example I called that php file ‘twitter-update.php’. Now that we have our simple proxy we can update our twitter status with a simple html form and a little ajax. I used the prototype framework for my javascript.

<script src="includes/prototype.js" type="text/javascript">
<script type='text/javascript'>
function update_twitter()
{
  var param_string = "username="+$('username').value+"&password="+
        $('password').value+"&update="+$('update').value;
  alert(param_string);
  var options = {
    method: "post",
    parameters: param_string,
    onSuccess: function (xhr, Json) {
      alert("Response received successfully.");
    },
    onFailure: function (xhr, Json) {
      alert("Request was unsuccessful.");
    }
  };
  
  var oRequest = new Ajax.Request("twitter-update.php", options);
}

</script>

Obviously this is for example purposes only and if you’re actually using it for production then you should edit it a lot. Now for the last little bit here’s the simple html form that starts it all.

User Name : <input type='text' id='username' value='codytaylor1234'><br>
Password  : <input type='password' id='password' value='mypassword'><br>
New Status : <input type='text' id='update' 
value='Twitter Update from html/javascript/php'><br>
<input type='button' value="Update Twitter" onclick='update_twitter();'>

Do you ever download those files that are comprised of multiple zip files that always seem to extract individual rar files to their own folders. This would normally require the user to cut and paste all these rar files back into the original folder and then unrar them. This is very tedious, especially when there is lots of these files and folders. I’ve written this little shell script to automate this task for myself and figured that I would share. This script is extremely simple but it has worked great for every double archive that I have tried it on. As always any improvements and comments are welcome.

Call this script from the command line when your current working directory is the folder with all the zip files in it. To get your current working directory use the command ‘pwd’.

unzip -o \*.zip
for f in *.rar;do unrar -o- e “$f”;done
rm *.rar
rm *.zip

You may be asking why I was forced to escape the ‘*’ in the first line. If I didn’t do this then I got a lot of “caution: filename not matched:” errors on the unzip line. Not sure why and if anyone can shed some light on that it would be great. As for the option to the commands, read the man pages. And the for loop is pretty self explanatory.

Enjoy those giant image sets.