6 ms·

The Bourne Shell Source Code

122 points by kick 7y ago

kick 7y ago
This is the source to the original Bourne Shell, shipped in Research UNIX v7. You've probably used GNU Bash, which stands for "Bourne-Again SHell." The Bourne sh is significant for a few reasons. Primarily, its GNU descendant is now installed on billions of devices. Perhaps of more interest: Bourne's sh source code heavily abuses C macros to look and feel like ALGOL-68. This is made more significant because it came before C was standardized: it took real knowledge to abuse that much. While this is C that compiled just fine for the day, and might compile mostly without errors for a compiler with a K&R compatibility mode, it's absolutely wild, and is written compensating for some of K&R's faults (see how it handles true v. false). I recommend mac.h as a file of particular interest: https://www.tuhs.org/cgi-bin/utree.pl?file=V7/usr/src/cmd/sh/mac.h https://www.tuhs.org/cgi-bin/utree.pl?file=V7/usr/src/cmd/sh... Bonus points to anyone who understands what these three lines are doing within it: #define LOBYTE 0377 #define STRIP 0177 #define QUOTE 0200 Also of interest: This was specifically the reason that the International Obfuscated C Code Contest was created, started just minutes after seeing Bourne's sh for the first time (I'm sorry for formatting this as code block, but the formatting breaks otherwise): Q: How did the IOCCC get started? A: One day (23 March 1984 to be exact), back Larry Bassel and I (Landon Curt Noll) were working for National Semiconductor's Genix porting group, we were both in our offices trying to fix some very broken code. Larry had been trying to fix a bug in the classic Bourne shell (C code #defined to death to sort of look like Algol) and I had been working on the finger program from early BSD (a bug ridden finger implementation to be sure). We happened to both wander (at the same time) out to the hallway in Building 7C to clear our heads. We began to compare notes: ''You won't believe the code I am trying to fix''. And: ''Well you cannot imagine the brain damage level of the code I'm trying to fix''. As well as: ''It more than bad code, the author really had to try to make it this bad!''. After a few minutes we wandered back into my office where I posted a flame to net.lang.c inviting people to try and out obfuscate the UN*X source code we had just been working on.
- eqvinox 7y ago
  > Bonus points to anyone who understands what these three lines are doing within it: #define LOBYTE 0377 #define STRIP 0177 #define QUOTE 0200 That's just 0xff, 0x7f and 0x80 in octal, and the high bit used to be a flag for all kinds of "magic" behaviour back when 7-bit ASCII was the norm...
  - teknopaul 7y ago
    I find myself validating a lot of input to be ascii still. I think its time to write a lib to make use of all those wasted bits.
    - teknopaul 7y ago
      I signed the above post with an emoticon that does not render? Could it be that hn is not 8bit safe?
      - detaro 7y ago
        HN filters out emoji (well, most of them, the blacklist appears to be incomplete)
        codetrotter 7y ago
        > the blacklist appears to be incomplete I was under the impression that the emojis that are not blacklisted are intentionally whitelisted. For example, all of the flag emojis are possible to use. That seems to be no coincidence. There are a few others that are possible to use as well, most of which appear to be logically grouped together. For example, multiple emojis relating to time are possible to use. The flags make sense I think. And I could see the ones relating to time being sort of relevant in post titles about time management for example. For some reason, some of the symbols resembling media playback controls are possible to use too. I don't see any reason for the media playback controls symbols to be available (while so many others are blacklisted I mean), but it does make the following possible though: "This is so sad. Alexa, play Despacito 2." Now playing: Despacito 2 (feat. Eminem) ⏯ ⏮ ⏭ —————————○—————— (2:01 / 3:14) Not that there is any immediate practical use of that of course. I think it would be interesting if the mods would comment on which emojis and other symbols outside of human writing systems are available and if indeed that is intended or not, and if intended what they are expecting people to use them for and why they decided to whitelist exactly those that they did while still blacklisting a few of the other ones that might be useful. It might just be like you said also though, maybe they explicitly blacklisted some symbols only and then more symbols were introduced later and the blacklist was never updated to include those.
JdeBP 7y ago
Interestingly, https://news.ycombinator.com/item?id=22188704 https://news.ycombinator.com/item?id=22188704 , with similar techniques reinvented 4 decades later, was on Hacker News only yesterday.
- kick 7y ago
  The technique of macroing C to death to look like another language never died! It's still a very popular thing to do, but it's gotten a bit less wild now that C has been standardized to death.
  - amyjess 7y ago
    I remember in college some friends of mine decided to macro C into really bad fake German. Think 'inten mainen" and 'printenoutenf'.
- kragen 7y ago
  Yes, I commented there about the Bourne Shell and the IOCCC: https://news.ycombinator.com/item?id=22192910 https://news.ycombinator.com/item?id=22192910
gyrator 7y ago
As someone who used the C preprocessor to generate CPP, Java, and C# from a common source in order to have a common library for native apps, I always appreciate a good bit of preprocessor abuse - it's one of the things that makes C so much fun!
- Koshkin 7y ago
  My favorite idea of an extreme preprocessing is using C itself as the preprocessor language, with, optionally, the only syntactic sugar being provided by ASP-like brackets.
drallison 7y ago
Back when I was writing C compilers the Bourne Shell was my nemesis. The Bourne shell did exercise nearly every "feature" of the C language. Compiling and then running the shell was a great test case for an optimizing compiler and turned up many bugs. But, when the compiled code failed, winding back to the underlying C through the all of the macros and optimizations was exceptionally difficult. I still remember many a late night trying to figure out what happened. (Thanks Steve, for many fascinating hours of struggle.)
silasdb 7y ago
The whole program trusts definitions in mac.h [1] like: #define IF if( #define THEN ){ #define ELSE } else { #define ELIF } else if ( #define FI ;} #define BEGIN { #define END } #define SWITCH switch( #define IN ){ #define ENDSW } #define FOR for( #define WHILE while( ... Isn't it nowadays considered bad practice? After taking a glance at the code, I see there might be some advantages like not forgetting to add missing {}. Is there any other explanation on why they created a dialect on the top of C using the preprocessor? [1] https://www.tuhs.org/cgi-bin/utree.pl?file=V7/usr/src/cmd/sh/mac.h https://www.tuhs.org/cgi-bin/utree.pl?file=V7/usr/src/cmd/sh... EDIT: fix English
- swiley 7y ago
  I’m under the impression that building up high level languages using macros was very common among assembly programmers, since C was new whoever wrote this may have come from assembly and taken the habit with them.
- kick 7y ago
  Bourne liked ALGOL. A lot. So much that he was one of the few people who wrote their own ALGOL-68 compiler. Using the preprocessor to feel more at home is a pretty good idea in this case. This wasn't particularly popular to anyone who wasn't, well, Bourne, even at the time. I posted an example here: https://news.ycombinator.com/item?id=22199664 https://news.ycombinator.com/item?id=22199664
- wgml 7y ago
  The author worked on ALGOL 68C and probably intended to reuse the more familiar syntax. Nowadays, I would indeed consider it a bad practice to use such macros. Especially if you intend to share the project with anyone else.
m0d0nne11 7y ago
I'm another who recalls this mess being used (1990 or so) as the acid test for C compilers, source code analyzers and debuggers. I can still picture the look of pride on a certain salesman's face when he demoed a valgrind-like tool for us that didn't just crumble to pieces when asked to chew on this tangle.
deleted 7y ago
[deleted]

122 points by kick 7y ago

kick 7y ago

This is the source to the original Bourne Shell, shipped in Research UNIX v7. You've probably used GNU Bash, which stands for "Bourne-Again SHell." The Bourne sh is significant for a few reasons. Primarily, its GNU descendant is now installed on billions of devices. Perhaps of more interest: Bourne's sh source code heavily abuses C macros to look and feel like ALGOL-68. This is made more significant because it came before C was standardized: it took real knowledge to abuse that much. While this is C that compiled just fine for the day, and might compile mostly without errors for a compiler with a K&R compatibility mode, it's absolutely wild, and is written compensating for some of K&R's faults (see how it handles true v. false). I recommend mac.h as a file of particular interest: https://www.tuhs.org/cgi-bin/utree.pl?file=V7/usr/src/cmd/sh/mac.h https://www.tuhs.org/cgi-bin/utree.pl?file=V7/usr/src/cmd/sh... Bonus points to anyone who understands what these three lines are doing within it: #define LOBYTE 0377 #define STRIP 0177 #define QUOTE 0200 Also of interest: This was specifically the reason that the International Obfuscated C Code Contest was created, started just minutes after seeing Bourne's sh for the first time (I'm sorry for formatting this as code block, but the formatting breaks otherwise): Q: How did the IOCCC get started? A: One day (23 March 1984 to be exact), back Larry Bassel and I (Landon Curt Noll) were working for National Semiconductor's Genix porting group, we were both in our offices trying to fix some very broken code. Larry had been trying to fix a bug in the classic Bourne shell (C code #defined to death to sort of look like Algol) and I had been working on the finger program from early BSD (a bug ridden finger implementation to be sure). We happened to both wander (at the same time) out to the hallway in Building 7C to clear our heads. We began to compare notes: ''You won't believe the code I am trying to fix''. And: ''Well you cannot imagine the brain damage level of the code I'm trying to fix''. As well as: ''It more than bad code, the author really had to try to make it this bad!''. After a few minutes we wandered back into my office where I posted a flame to net.lang.c inviting people to try and out obfuscate the UN*X source code we had just been working on.

eqvinox 7y ago
> Bonus points to anyone who understands what these three lines are doing within it: #define LOBYTE 0377 #define STRIP 0177 #define QUOTE 0200 That's just 0xff, 0x7f and 0x80 in octal, and the high bit used to be a flag for all kinds of "magic" behaviour back when 7-bit ASCII was the norm...
- teknopaul 7y ago
  I find myself validating a lot of input to be ascii still. I think its time to write a lib to make use of all those wasted bits.
  - teknopaul 7y ago
    I signed the above post with an emoticon that does not render? Could it be that hn is not 8bit safe?
    - detaro 7y ago
      HN filters out emoji (well, most of them, the blacklist appears to be incomplete)
      - codetrotter 7y ago
        > the blacklist appears to be incomplete I was under the impression that the emojis that are not blacklisted are intentionally whitelisted. For example, all of the flag emojis are possible to use. That seems to be no coincidence. There are a few others that are possible to use as well, most of which appear to be logically grouped together. For example, multiple emojis relating to time are possible to use. The flags make sense I think. And I could see the ones relating to time being sort of relevant in post titles about time management for example. For some reason, some of the symbols resembling media playback controls are possible to use too. I don't see any reason for the media playback controls symbols to be available (while so many others are blacklisted I mean), but it does make the following possible though: "This is so sad. Alexa, play Despacito 2." Now playing: Despacito 2 (feat. Eminem) ⏯ ⏮ ⏭ —————————○—————— (2:01 / 3:14) Not that there is any immediate practical use of that of course. I think it would be interesting if the mods would comment on which emojis and other symbols outside of human writing systems are available and if indeed that is intended or not, and if intended what they are expecting people to use them for and why they decided to whitelist exactly those that they did while still blacklisting a few of the other ones that might be useful. It might just be like you said also though, maybe they explicitly blacklisted some symbols only and then more symbols were introduced later and the blacklist was never updated to include those.

JdeBP 7y ago

Interestingly, https://news.ycombinator.com/item?id=22188704 https://news.ycombinator.com/item?id=22188704 , with similar techniques reinvented 4 decades later, was on Hacker News only yesterday.

kick 7y ago
The technique of macroing C to death to look like another language never died! It's still a very popular thing to do, but it's gotten a bit less wild now that C has been standardized to death.
- amyjess 7y ago
  I remember in college some friends of mine decided to macro C into really bad fake German. Think 'inten mainen" and 'printenoutenf'.
kragen 7y ago
Yes, I commented there about the Bourne Shell and the IOCCC: https://news.ycombinator.com/item?id=22192910 https://news.ycombinator.com/item?id=22192910

gyrator 7y ago

As someone who used the C preprocessor to generate CPP, Java, and C# from a common source in order to have a common library for native apps, I always appreciate a good bit of preprocessor abuse - it's one of the things that makes C so much fun!

Koshkin 7y ago
My favorite idea of an extreme preprocessing is using C itself as the preprocessor language, with, optionally, the only syntactic sugar being provided by ASP-like brackets.

drallison 7y ago

Back when I was writing C compilers the Bourne Shell was my nemesis. The Bourne shell did exercise nearly every "feature" of the C language. Compiling and then running the shell was a great test case for an optimizing compiler and turned up many bugs. But, when the compiled code failed, winding back to the underlying C through the all of the macros and optimizations was exceptionally difficult. I still remember many a late night trying to figure out what happened. (Thanks Steve, for many fascinating hours of struggle.)

silasdb 7y ago

The whole program trusts definitions in mac.h [1] like: #define IF if( #define THEN ){ #define ELSE } else { #define ELIF } else if ( #define FI ;} #define BEGIN { #define END } #define SWITCH switch( #define IN ){ #define ENDSW } #define FOR for( #define WHILE while( ... Isn't it nowadays considered bad practice? After taking a glance at the code, I see there might be some advantages like not forgetting to add missing {}. Is there any other explanation on why they created a dialect on the top of C using the preprocessor? [1] https://www.tuhs.org/cgi-bin/utree.pl?file=V7/usr/src/cmd/sh/mac.h https://www.tuhs.org/cgi-bin/utree.pl?file=V7/usr/src/cmd/sh... EDIT: fix English

swiley 7y ago
I’m under the impression that building up high level languages using macros was very common among assembly programmers, since C was new whoever wrote this may have come from assembly and taken the habit with them.
kick 7y ago
Bourne liked ALGOL. A lot. So much that he was one of the few people who wrote their own ALGOL-68 compiler. Using the preprocessor to feel more at home is a pretty good idea in this case. This wasn't particularly popular to anyone who wasn't, well, Bourne, even at the time. I posted an example here: https://news.ycombinator.com/item?id=22199664 https://news.ycombinator.com/item?id=22199664
wgml 7y ago
The author worked on ALGOL 68C and probably intended to reuse the more familiar syntax. Nowadays, I would indeed consider it a bad practice to use such macros. Especially if you intend to share the project with anyone else.

m0d0nne11 7y ago

I'm another who recalls this mess being used (1990 or so) as the acid test for C compilers, source code analyzers and debuggers. I can still picture the look of pride on a certain salesman's face when he demoed a valgrind-like tool for us that didn't just crumble to pieces when asked to chew on this tangle.

deleted 7y ago

[deleted]