A Real Bourne Shell for Linux?

the_code_poet asks: "I'm a lead developer for a software development company, and one of my responsibilities has been writing an installer for our product (of which Linux is one of the platforms). In keeping with UNIX tradition, the installer is written in shell (thats /bin/sh), but as many of you know there is no Bourne shell for Linux - only bash. This has caused inconsistencies (mostly bugs in bash) when writing a generic UNIX sh script that works fine on commerical *NIX's." For a semi-complete list of differences between bash and sh, you will want to check out section C1 of the Bourne Again Shell FAQ. To be honest, I have yet to run into much trouble with a script starting with #!/bin/sh with /bin/bash, and I've been using the latter for years. If any of you have had problems related to this, please tell us what the problem was and how you solved it. Also: would anyone out there be interested in writing a real Bourne Shell for Linux?

"On every distro I've ever seen /bin/sh is just a soft link to /bin/bash. If bash is invoked with sh as its name (argv[0]) then its supposed to act like Bourne - but that just doesnt happen (for example: export FOO=bar is *not* valid Bourne shell syntax, you must say FOO=bar; export FOO)

Do you think that the startup scripts for most distributions would break because, even though they say #!/bin/sh at the top, they REALLY mean #!/bin/bash?

Given that there is no real Bourne shell for Linux, and that bash has an exhorbitant file size. Quoting bash's man page, here: '...it's too big and too slow' for something that is to be used as the defacto-standard shell for scripting, do you think its a worthy venture to set out to write a small, tight, pure Bourne shell?

*asbestos disclaimer*: This has nothing to with Bash as an interactive user shell and has nothing to do with a holy war over who's favorite shell is better than whomever's."

While doing a small bit of research on this question, I noted there was another Bourn-compatible shell out there called "ash", yet it's billed as doing "some things better and some things worse than bash". Does anyone use it, and find it better than bash for their shell scripting needs?

Comments

It's a non-issue.

[mindstrm]

You are looking for a solution to a problem that does not exist.

bash is backward compatable to sh. Period.

Yes, you can do things in bash you can't do in sh, but not vice-versa.

If you write your scripts for stock Bourne, they will run fine under bash.

Did you even read the complaint?

[Wakko Warner]

The guy writes installer scripts for a living. Every other unix has a Bourne shell implementation except Linux, and Linux's /bin/bash has incompatibilities. Telling the guy to fuck off and use something else has got to be the most ignorant thing I've ever heard. I'm sure he can tell his boss the same thing, right? "Fuck this, I'm gonna use ksh so it works on... AIX only!"

Ask Slashdot becomes less helpful by the nanosecond.

- A.P.

Which direction are you worried about?

[MarkusQ]

I think that there is some confusion here. The_code_poet clearly asked about compatibility going from sh to bash (i.e., he wants to write standard sh scripts and have them work on linux, and therefore bash). But the incompatibilities everyone is discussing (e.g. initialized export syntax) are all going the other way; things that you can write under bash that won't work under sh. So what?

The things that matter are first, the things sh has that bash does not (from the FAQ):

* uses variable SHACCT to do shell accounting
* includes `stop' builtin (bash can use alias stop='kill -s STOP')
* `newgrp' builtin
* turns on job control if called as `jsh'
* $TIMEOUT (like bash $TMOUT)
* `^' is a synonym for `|' * new SVR4.2 sh builtins: mldmode, priv

...and the implementation differences:

* redirection to/from compound commands causes sh to create a subshell
* bash does not allow unbalanced quotes; sh silently inserts them at EOF
* bash does not mess with signal 11
* sh sets (euid, egid) to (uid, gid) if -p not supplied and uid < 100
* bash splits only the results of expansions on IFS, using POSIX.2 field splitting rules; sh splits all words on IFS
* sh does not allow MAILCHECK to be unset (?)
* sh does not allow traps on SIGALRM or SIGCHLD
* bash allows multiple option arguments when invoked (e.g. -x -v); sh allows only a single option argument (`sh -x -v' attempts to open a file named `-v', and, on SunOS 4.1.4, dumps core. On Solaris 2.4 and earlier versions, sh goes into an infinite loop.)
* sh exits a script if any builtin fails; bash exits only if one of the POSIX.2 `special' builtins fails

None of these seem to me to be show-stoppers if you are writing the script from scratch (or even porting a reasonably written one)--I mean really, are you counting on it to dump core if you use multiple option arguments? Is there some reason you can't ballane your quotes? So my question to the_code_poet is, what exactly are you trying to do in sh that won't work in bash?

--MarkusQ