Beneath the beautiful Mac OS X interface lies an industrial-strength UNIX system, many of the key UNIX-based scientific applications are now available under Mac OS X. While many users feel very comfortable in the command-line environment AppleScript offers a means to access the UNIX foundations without the need to remember a series of UNIX commands. However as you might expect there are a few things that you need to be aware of when linking AppleScript and UNIX.

Leading you up the garden path

Applescript uses the colon “:” as a separator for directories however UNIX uses POSIX (Portable Operating System for UNIX) file paths in which the slash “/” is used as the directory separator. This could cause obvious problems, however one of the additions to AppleScript 1.8 was the ability to interconvert the two file reference systems.

Open up Script Editor and type/copy :-

The first line allows the user to select a file, the second line converts the file reference to text and then it is displayed. The fourth line converts the Apple file reference to the POSIX path and then displays it. Of course you need to be able to do the reverse translation and the “POSIX file” command converts the POSIX path to a Mac OS X path as shown below.

Here is a very simple example of how this can be used, this takes a Macintosh Path to a folder, converts it to the POSIX path. The script then runs the Shell command “ls” to list the contents of the directory and displays the result.

Whilst this works perfectly in most cases there are a couple of issues you should be aware of, a file or folder name may contain characters which need to be escaped to be passed to a shell command. Use quoted form to get the quoted form of a string. For example if a directory name contains a space.

Come out from under that shell

The default shell for Mac OS X is BASH and I don’t want to get into a debate about the relative merits of the different shells that are available, the important thing to remember when running a “Do shell script” command is that do shell script always uses /bin/sh to interpret your command, not your default shell. So commands that work fine in the Terminal may not work when called using the “Do shell script” command. In addition when you use just a command name instead of a complete path, the shell uses a list of directories (known as your PATH) to try and find the complete path to the command. For security and portability reasons, do shell script ignores the configuration files that an interactive shell would read, so you don’t get the customizations you would have in Terminal. You need to use the full path to the command.

Compare the results of these two applescripts:

Should give you something like “/usr/bin:/bin:/usr/sbin:/sbin”

On the other hand this applescript

Will give you the complete PATH as defined in your .profile.

Having a little Fun with UNIX

This script gets a list of all the applications in the Applications folder, then finds those applications that contain the capital letter “B”, then sorts them into reverse alphabetical order and displays the result. The “|” is the pipe command, the pipe command is one of the most important commands in UNIX because it allows us to create powerful functions in a single statement. The pipe command is represented with the | character and it is used to connect the output from one command and send it as input to another command. On a Mac keyboard it is on the right-hand side next to the return key.

Here is a fun feature:-

Run this script and then paste into a text editor, (I used BBEdit) and you should see this months calendar. Replace “cal” with “cal 10 1492” and you can see the month in 1492 when Christopher Columbus landed on a Caribbean Island.

Give me some input

This is the mechanism by which iBabel searches chemical information, of course iBabel was built using Xcode which allows the construction of rich user interfaces, and hopefully that will be the subject of a future tutorial. However we can use Applescript to provide a limited user interface, the following script asks the user to choose a file, it then uses the UNIX commandline tool OpenBabel to convert the file to the format chosen in the second dialog box and then saves it to the desktop. You will need to have installed OpenBabel You could have yet another dialog box asking to choose where to save the file but I think you can see why Xcode would be a better option.

It should be noted that the latest version of OpenBabel now uses obabel not babel.

Print Folder Contents Applescript

I recently needed a list of all files in a particular folder, actually the folder contained sub-folders also containing files. This tedious task becomes trivial with a couple of UNIX commands and Applescript provides a convienient user interface and the glue between the different UNIX commands.

The script is shown colour coded below. The first part of the script simply asks the user to choose the folder they want to print, and then generates a UNIX compatible POSIX path. The next part generates a temporary file to save the output into. 

The next dialog asks the user if they only want to print this folder or to include sub-directories. If the response is to only print this folder then the UNIX command:

Can be used to list the directory and send the output to the temporary file.

Alternatively the command:

Works recursively through the file structure listing all the files and formats the output into a multi-column format.

The final part of the script prints the temporary file.

The script can be downloaded from here.

Last Updated 6 March 2023

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