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164 lines
6.3 KiB
Markdown
164 lines
6.3 KiB
Markdown
# GETCD: MS-DOS .BAT Utility For Locating CD-ROM Drive
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`GETCD.COM` is "batch utility" for MS-DOS to assist in locating a
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CD-ROM drive based on file search. It is similar to `FINDCD.EXE`
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with the following exceptions
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- it takes an argument to specify a file
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- automatically creates/manages the CDROM= variable
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It is written in NASM assembler; and is mostly the thing I wrote
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while ~~attempting to learn~~ learning assembler.
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## Usage
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`GETCD.COM` does not display much in the way of user output. The
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largest chunk can be seen by calling the basic help:
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`getcd /?`
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If you were to "place a CD" in a "CD drive" with the file what.txt
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on it and ran this:
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`getcd what.txt`
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It looks like nothing happened. However, if you call `set` from the
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command prompt to see the current variables; you should see `CDROM=D:`
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(or whatever the actual drive letter is) now exists.
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`getcd` on it's own will default to a wildcard (*) search. This has
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the effect of returning the first CD drive that has a disc in it, or
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doesn't return some kind of error.
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Wildcards are allowed in the search string; as well as just directory
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names. The first drive that doesn't fail search is returned.
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`NO ENV FREE` is the only displayed error message if you don't have
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enough environment space free. Most failures should result in nothing
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being changed. This plays well with being a batch utility:
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```
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@echo off
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set CDROM=0:
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getcd what.txt
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if %CDROM%=0: goto nocd
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(do stuff)
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goto exit
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nocd:
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(stuff for no cd)
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exit:
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```
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Additionally, you can look for errorlevel 255, which is returned if
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there are no CDROM drives.
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### Adapting scripts for FINDCD.EXE
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You'll just need to modify `FINDCD` to `GETCD [file]`
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### My scripts want a \ in the variable
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`GETCD` is kind of picky in that it will make the CDROM variable
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a drive letter, a colon, and no backslash. I may change this by
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assuming an extra character is a backslash an not delete it.
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But, for now; just do this in your .bat
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```
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set CDROM=%CDROM%\
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```
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## What does this do?
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- It lets you specify a file to search CD-ROM drives for and puts
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that drive letter in to the CDROM= environment variable. Then
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fancy .BAT scripts can go `call %CDROM%\install.bat` and
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run the .bat off the CD.
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## How does it differ from other utilities?
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- The only utility I've actually found has been FINDCD.EXE. The
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alternative is apparently for loops. I've seen mentions of other
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utlities on sites devoted to .bat scripting; but never found an
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exe.
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The differences from FINDCD are passing a filename as an argument
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and the automatic management of the variable. FINDCD used a hard
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coded file in the binary as well as requiring you to preset the
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variable.
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I decided to just toss all that aside and assume the user might
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not do it right; or in the case of FINDCD; the variable length
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pre-set is longer than necessary. I have no clue what FINDCD is
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doing with the variable.
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## Building
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`nasm -o getcd.com getcd.asm`
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The build system was FreeDOS with WatcomC, DJGPP, IA16, and a few other things on it.
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It was tested on MS-DOS 6.22 under an 86Box emulated 486/DX4 100.
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## Random Things Passed As FAQ:
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**Why a .COM and not a .EXE?**
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- We didn't need any of the fancy options a .exe gave us. Our binary is not over 65kB in size and doesn't have to be relocated to run. That is primarily what .exe would give me; the ability to relocate my code once loaded. I could have assembled this to an object file then linked it to an .EXE, but I still wouldn't be using any "EXE features"
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**What are the minimum requirements?**
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- DOS 3.3 and a CD-ROM drive. The program doesn't use much ram and
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while will technically run on an 8088, the lack of CD-ROM drivers
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are a bigger issue.
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**Will this work on FreeDOS?**
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- Yes, it's been known to. I have not tested the memory manipulating
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version; but early versions worked.
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**What about n-DOS?**
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- No comment. It *should*, but it will depend if your CD-ROM extensions
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respond to the interrupts I use.
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**Why did you do this?**
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- I'd wanted to see if I could write x86 ASM for quite some time. I
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hadn't learned ASM beyond knowing how CPU's work at a low level
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and what ASM was. I had an incorrect assumption that I didn't know
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the levels of math required to make it work that I'd held for years.
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Anyway; I'd also incorrectly assumed after diving in that the magic
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of low-level would give me a secret way to look at drives without
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triggering errors. It did; but changing the interrupt vector isn't
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ASM specific..it was, like most things; a concept I'd heard about
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but really didn't undertand back in my teens when I first tried.
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I almost gave up and went to C when I was just trying to get the
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byte in the env block realizing that's why people have libaries.
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And, no; what little I read about the subject involved inline ASM.
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My most optimized version was 98 bytes. Yes, 98. It had no file
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argument or memory management. You had to make the environment;
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variable, it put the letter at the byte after =, and that was it.
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Then I decided to add features for the sake of stability and users;
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plus what good is a clone if you don't improve it.
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So despite serving no real purpose and being a huge time-sink for
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something only I'll probably use; I'm at least better in ASM than
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when I started. Huge bar given I started at almost zero.
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## License
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MIT No Attribution
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Copyright 2024 Jay Moore
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Permission is hereby granted, free of charge, to any person obtaining a copy of this
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software and associated documentation files (the "Software"), to deal in the Software
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without restriction, including without limitation the rights to use, copy, modify,
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merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
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permit persons to whom the Software is furnished to do so.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
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INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
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PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
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HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
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OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. |