Setting Up Pre/Post Processing

HST Server can be configured to run scripts that are triggered by session start, session stop, file start, and file stop.

Your Aspera server can automatically execute a shell script from a pre-defined location:

/opt/aspera/var/

The script is executed as a result of four transfer events:

Session start
Session end
Start of each individual file transfer in the session
End of each individual file transfer in the session

The aspera-prepost script can also execute additional shell scripts, Perl scripts, native executables, and Java programs.

Environment Variables: Aspera has several environment variables for aspera-prepost that you can use in your own custom scripts. These environment variables are described in detail in Pre/Post Variables. Depending on usage, pre- and post-processing may consume a large amount of system resources. Be sure to evaluate your system performance and apply this feature appropriately.

CAUTION:

When creating pre- and post-processing scripts, unsafe scripts can compromise a server. As with CGI scripts, you should take precautions in testing a pre/post script before placing it into use (such as taint checking and ensuring proper quotes). You should also be aware of user permissions; pre/post scripts run as the user who authenticates the transfer. To prevent a pre/post script from performing an action with elevated or special user permissions, the script needs to check the $USER variable.

To set up pre/post processing for your Aspera transfer product:

Set up the shell script file.
Locate the following file:
```
/opt/aspera/var/aspera-prepost.disable
```
This file runs the Perl script aspera-notif.pl, which is an email notification script that sends emails (according to user-defined filters) to one or more recipients. Filters and lists are defined in the Aspera configuration file aspera.conf, which is located in /opt/aspera/etc.

Copy the contents of aspera-prepost.disable into a new file, and name it as follows:
```
/opt/aspera/var/aspera-prepost
```
Ensure that execute privileges are enabled (at least r-xr-xr-x).
Create your scripts.
The pre/post processing script, aspera-prepost, can contain the pre/post processing steps, as well as execute other programs. Often, aspera-prepost checks for certain conditions (based on environment variables), and then calls a specific external executable based on those conditions.
aspera-prepost is executed as a result of a the start and end of a transfer session, as well as the start and end of the transfer of an individual file in the session. Use the variables TYPE and STARTSTOP to specify a particular state. For the complete list of all variables, see Pre/Post Variables.
Include custom scripts in aspera-prepost.
Custom scripts can be written directly into the script file aspera-prepost. For example, to add the custom script script1.pl to your pre/post script, insert the following line (into aspera-prepost):
```
...
perl script1.pl
...
```