Call Perl and Python Scripts from LabVIEW

The ability to call and re-use existing code can save a developer time and money. LabVIEW gives users the ability to directly access and integrate code written in a variety of languages. This article explains how to re-use test scripts developed in either the Perl or Python scripting languages using the System Exec VI in LabVIEW.

Perl and Python are high-level programming languages that use an interpreter to translate the source code into an executable format at run time instead of being pre-compiled. An interpreter, such as ActivePerl or ActivePython, is necessary to execute this translation.

Calling the Script Interpreter

Calling the interpreter can be simplified by changing the Environment Path Variable to include the location where your interpreter and corresponding library files are saved. You can edit the Environment Path using the System Properties Editor. You will need to ensure that the Environmental Path Variable is modified to include the directory in which the Interpreter and corresponding library files are located in order for the machine to recognize the Perl and Python tokens as commands to use the interpreter.

1. Right-click on My Computer  and select Properties.
2. Select the Advanced tab.
3. Click Environment Variables.
4. In System Variables, select the Path variable, and then click Edit.
5. Add the directory for where your Interpreter is saved.

Note: This example was prepared using the Using the ActivePerl 5.10.0 Interpreter and the ActivePython  2.6.1 Interpreter, which can be downloaded from the External Link: APSN ActivePerl Website and External Link: ActiveState ActivePython Website, respectively. Both Installers have built in functionality to edit the Environmental Path Variable to include the directory location of the interpreter and corresponding library files.
 

Calling Perl and Python Scripts From the Command Line

1. Select Start»Run
2. Enter cmd to launch the command line
3. Navigate to the directory where the Perl or Python script is saved
4. To call the interpreter that will execute the script use the following command(s):

For Perl scripts, use:  'perl scriptName.pl argument' as shown in the image below.
 

For Python scripts, use:  'python  scriptName.py argument' as shown in the image below.


 

Calling Perl and Python Scripts from LabVIEW

In LabVIEW you can use the System Exec.vi to execute a system-level command line that can include any parameters supported by the application you want to launch. This VI can be used to call a command line argument that will launch the Perl or Python script. Ensuring that your Environment Path Variable includes the directory in which you Interpreter and corresponding library files are saved will allow any System Exec call to recognize the perl and python tokens as commands to use the Perl and Python Interpreters to execute the script.

To call a Perl or Python script from LabVIEW you will need to pass in the following parameters to the System Exec.vi

• command line: indicates the command LabVIEW calls to run a program. If the executable is not in a directory listed in the PATH environment variable, the command line must contain the full path to the executable.
• working directory: the file system directory from which you want to execute the command.

Using the Attached LabVIEW Code

1. Set-up your Environment Path Variable to include the directory in which your Interpreter is saved
2. Save the TestScripts folder to your machine. This folder includes a Perl and Python script as well as LabVIEW code that is generated to call these scripts.
3. Open the TestScripts Folder and launch the TestVI.vi by double-clicking on it
4. Configure the TestVI to include:
   1. Working directory: The directory where you have saved the TestScripts folder <Path>\TestScripts
   2. Command line: The command you will send to the command line
      1. PERL SCRIPTS:  perl MyScripts.pl argument
      2. PYTHON SCRIPTS:  python MyScript.py argument
5. Click the Run arrow to execute the program