ALL05 - External command processors

Scripting your Workplace Shell the easy way

Christian Langanke

netlabs.org

Overview

• Scripting ? What for ?
• Conventional scripting with CMD.EXE
• Integration of external processors
• Reasons for using an EXTPROC
• EXTPROC invocation/parameter handling
• EXTPROC examples
• Problems
• Example Demo
• Future wishlist for scripting support

Scripting ? What for ? (1/2)

• Encapsulate complex tasks
  • execute a long list of commandline actions (batch job)
  • hide complex commands with special parameters (alias functionality)

• control/configure applications
  • create/maintain/delete WPS objects
  • configure WPS or application settings in USER or SYSTEM ini
  • control PM apps (well-known sample PM App: PM Globe)

Scripting ? What for ? (2/2)

• Provide extensions (user exits) to existing applications
  • Wireless LAN Monitor
  • ... others ...

  
  

• Scripting in that sense does NOT mean:

  write an application or large parts in scripts
  (would be considered to be application development)

  • EPM-style REXX Script (E language) part of EPM
  • GUI REXX applications

Conventional scripting with CMD.EXE

• internal commands of CMD.EXE, like:

  COPY DEL SET IF FOR ECHO PAUSE START ...
  (also usable directly on command line)

• script-only commands like: GOTO SHIFT

• all executables on the system
  • sytem provided like: XCOPY ATTRIB REPLACE ...
  • application package provided
• Scripts have to be named
  • *.cmd for OS/2 & eComStation scripts
  • *.bat for DOS scripts (implicitely launch a DOS Box)

Integration of external processors

• script file is processed by external script external instead of by CMD.EXE
• REXX as an external script processor is seamlessly integrated by CMD.EXE
  • scripts are (/still need to be) called *.cmd
  • first two characters being "/*" let CMD.EXE call the REXX interpreter to process the script
  • environment variables of CMD.EXE can be modified by REXX script (unlike in AIX or Windows ports of REXX !!!)
  • OS/2 or eComstation commands can be executed from the REXX script
• any other script engine can be explicitely integrated as an external command processor by the EXTPROC command in a CMD script file

Reasons for using an EXTPROC

• interface for application features for scripts with easy syntax
  • better addresses the average end user than normal scripting or REXX
• much more efficient for scripting than executables with lots of parameters
• easy to implement where a string interface has to be adressed anyway
  Examples:
  • FTP input file creation and execution for automated FTP operations
  • Multimedia Command Interface (MCI) for controlling MM devices
  • Workplace Shell (WPS) object creation and configuration
• integration of application features possibly not as good as with REXX, but syntax more suitable, less knowledge required

EXTPROC Invocation

• An external command processor
  • must accept the name of the script as a command line parameter
  • must read the script file, interpret and process the contained commands
  • can be implemented by any language, providing an executable or CMD
    • a normal batch file will not do, as its syntax cannot read a file and interpret it
    • REXX will just do fine !
• The EXTPROC command is specified first line of a CMD script (otherwise it is ignored)
  • first parameter: exectuable name of the command processor, passed to processor
  • more parameters: passed over to the processor before (!) the script name
  • Parameters to the script are passed over to the command processor as additional parameters after the script name

EXTPROC parameter handling

• sample command processor: showparms.cmd
  (only shows supplied parameters here)

  @ECHO OFF
   ECHO showparms called with: %1 %2 %3 %4 %5 %6 %7 %8 %9
   REM ... more code implementing commands would follow here ...
  

• scriptfile: test.cmd

  EXTPROC showparms /s1 /s2
    ... more showparms script code would follow here ...
  

• command executed on commandline:

  test /c1 /c2

• output is:

  showparms called with: /s1 /s2 test.cmd /c1 /c2
  

EXTPROC example: Batch FTP

• bftp.cmd implements the following commands for FTP transfer: (would require at least a short REXX script)

  OPEN USER PASSWD CD LCD PUT GET LS QUIT
  

• test.cmd downloads the Wireless LAN Monitor V3.00 package to the local directory of d:\downloads\xwlan
  • NOTE: always use your email address as password for anonymous FTP!

  EXTPROC BFTP
  OPEN ftp.netlabs.org
  USER anonymous
  PASSWD -myemail@gmx.de
  LCD d:\downloads\xwlan
  CD /pub/wlan
  GET xwlan300.zip
  QUIT
  

EXTPROC example: MCI

• mci.cmd/mcipm.cmd implement commands of Multimedia Command Interface (MCI) (marked green), batch labels and extra commands:

  ECHO GOTO PAUSE PLAYTRACK TRACE
  

• playlist.cmd plays track 3 and 4 of the inserted audio CD in a loop until stopped by Ctrl-Break

  EXTPROC MCI
  echo Playing track 3 and track 4 forever
  echo Press Ctrl-Break twice to exit ...
  open cdaudio alias playcd shareable wait
  :playtrack
  playtrack playcd 3 wait
  playtrack playcd 4 wait
  goto playtrack
  close playcd wait
  

EXTPROC example: Object Generator

• objgen.cmd implements commands for maintaining WPS objects and INI entries, environment variable support and some extra commands:

  TITLE CLASS LOCATION ID OPTION ENV SAY INI ...
  

  Extra environment variables provided by OBJGEN:

  BOOTDRV CALLDRV CALLDIR 
  

• mycfg.cmd creates a program object for editing config.sys

  EXTPROC OBJGEN
  CLASS      WPProgram
  TITLE      Edit config.sys
  LOCATION   <WP_DESKTOP>
  ID         <MYAPP_EDITCFGSYS>
  PROGTYPE   PM
  EXENAME    EPM.EXE
  PARAMETERS %BOOTDRV%\config.sys
  

Problems

• only the name of the scriptfile is passed to the EXTPROC (required: fully qualified path)

  • Bug in CMD.EXE !

• Resulting problem: the script being executed must reside in the current directory on the current drive, otherwise the command processor will not find it

• Partial workaround: search the PATH for the script, if it cannot be found. But: that may
  • still not find the script called
  • even call a different version of the script

Example Demo

• Batch FTP
• MCI Processor
• Object Generator

Future wishlist for scripting support

• Path/drive problem for the processor executable in EXTPROC command must be fixed!

• CMD.EXE should obey file associations when searching PATH
  • would allow to search other file extensions for scripts than only CMD (see PATHEXT under Windows)
• CMD.EXE should offer an interface to maintain the environment of the calling instance of it (like with REXX)

Q & A

• Your questions
• Your remarks
• Your suggestions

The Author

• Name: Christian Langanke
• email: cla@clanganke.de
• homepage: http://www.clanganke.de
  • with free programs for OS/2 and eComStation
  • my PGP key
• Member of Team OS/2 Germany
• OS/2 user since 1990 with OS/2 V1.2

My projects and activities

• author/inventor of projects
  • Wireless LAN Monitor
  • Workplace Shell Toolkit
  • Netlabs EPM Distribution
  • Internet Assistant for OS/2 and eComStation
• netlabs.org support activities
  • Generic MAC Wrapper driver (Release Management)
  • Port of WPA supplicant (Maintenance)
  • Everblue (Build System)
  • ISDNPM a.k.a. eCSCoNet (Online Help, REXX scripts)
• planning or supporting events of
  • Team OS/2 Germany local fairs
  • Warpstock Europe events

The End

Thank you very much for your your attention!