Many iSeries/i5 professionals think of Qshell and i5/OS Portable Application Solutions Environment (PASE) almost interchangeably. Both environments provide access to an integrated UNIX environment without the need to manage a separate partition. In addition, both offer a command shell (a program that runs commands interactively or from a script) and the ability to run UNIX commands, utilities, and programs.

Qshell and i5/OS PASE even have similar-looking terminal environments (Figures 1 and 2).

Figure 1: Qshell Command Entry looks almost identical to PASE (Figure 2, below). (Click images to enlarge.)

Figure 2: PASE's default Korn shell (also known as "-sh") strongly resembles Figure 1.

Qshell and PASE have separate sets of utilities and commands. Some, such as ls and cd, are present in both environments, while others, such as diff, are present in one but not the other.

Does that mean we should choose an environment based on the commands we wish to use? Perhaps, but it is not a requirement. Qshell and PASE can execute each other's utilities and commands. For example, in "Vive la Diff," I showed how to use PASE's diff command. I stated that this command ran more easily in PASE than in Qshell. Reader Randy Adamski asked me directly, "Is it possible to run this command in Qshell?" The answer was "Yes," but that it required locating the command in PASE's default command path, /QOpenSys/usr/bin.

One definite difference is that Qshell is EBCDIC-based and PASE is ASCII-based. To put Qshell to the test, I asked Qshell to execute PHP, an AIX binary that I normally run in PASE. PHP is an ASCII-encoded program. Did it work in Qshell? Yes. I ran the PHP –v command to show PHP's version information, presumably encoded in ASCII. Qshell translated the results into its EBCDIC environment, proudly showing me the result:

PHP 4.3.9 (cgi) (built: Feb 4 2005 15:04:33)
Copyright (c) 1997-2004 The PHP Group
Zend Engine v1.3.0, Copyright (c) 1998-2004 Zend Technologies
$      

Just as Qshell often is able to reverse its EBCDIC nature when needed, ASCII-based PASE can access EBCDIC system resources. PASE does this with its commands:
qsh (call a Qshell command) and system (call a native i5/OS command).

How to Choose

I asked IBM's Walt Madden when we should choose one environment over the other. He suggested, "You might choose i5/OS PASE over Qshell if the program you are trying to run already exists in the UNIX (especially AIX) space. Conversely, you might choose Qshell over i5/OS PASE if the program needs to be tightly coupled to i5/OS ILE APIs."

Additional Resources

This Qshell tutorial is a fine introduction to Qshell. To go further, read the definitive Qshell resource, Qshell for iSeries, by Ted Holt and Fred A. Kulack. To learn about PASE, try this excellent introductory PASE article by Walt Madden. Also see the official PASE documentation.