00d439605f
When exporting variables, ksh exports their attributes (such as
'integer' or 'readonly') in a magic environment variable called
"A__z" (string defined in e_envmarker[] in data/msg.c). Child
shells recognise that variable and restore the attributes.
This little-known feature is risky; the environment cannot
necessarily be trusted and that A__z variable is easy to manipulate
before or between ksh invocations, so you can cause a script's
variables to be of the wrong type, or readonly. Backwards
compatibility requires keeping it, at least for now. But it should
be disabled in the posix mode, as it violates POSIX.
To do this, we have to solve a catch-22 in init.c. We must parse
options to know whether to turn on posix mode; it may be specified
as '-o posix' on the command line. The option parsing loop depends
on an initialised environment[*], while environment initialisation
(i.e., importing attributes) should depend on the posix option.
The catch-22 can be solved because initialising just the values
before option parsing is enough to avoid regressions. Importing the
attributes can be delayed until after option parsing. That involves
basically splitting env_init() into two parts while keeping a local
static state variable between them.
src/cmd/ksh93/sh/init.c:
- env_init():
* Split the function in two stages based on a new
'import_attributes' parameter. Import values in the first
stage; import attributes from A__z in the second (if ever).
Make the 'next' variable static as it keeps a state needed for
the attributes import stage.
* Single point of truth, greppability: don't hardcode "A__z" in
separate character comparisons, but use e_envmarker[].
* Fix an indentation error.
- sh_init(): When initialising the environment (env_init), don't
import the attributes from A__z yet; parse options first, then
import attributes only if posix option is not set.
src/cmd/ksh93/sh/name.c:
- sh_envgen(): Don't export variable attributes to A__z if the
posix option is set.
src/cmd/ksh93/tests/attributes.sh:
- Check that variable attributes aren't imported or exported
if the POSIX option is set.
src/cmd/ksh93/sh.1:
- Update.
This was the last item on the TODO list for -o posix for now.
Closes: #20
[*] If environment initialisation is delayed until after option
parsing, bin/shtests shows various regressions, including:
restricted mode breaks; the locale is not initialised properly
so that multibyte variable names break; $SHLVL breaks.
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| .github/workflows | ||
| bin | ||
| docs | ||
| lib/package | ||
| src | ||
| .gitignore | ||
| LICENSE.md | ||
| NEWS | ||
| README.md | ||
| TODO | ||
KornShell 93u+m
This repository is used to develop bugfixes to the last stable release (93u+ 2012-08-01) of ksh93, formerly developed by AT&T Software Technology (AST). The sources in this repository were forked from the Github AST repository which is no longer under active development.
To see what's fixed, see NEWS and click on commit messages for full details.
To see what's left to fix, see TODO.
Policy
- No new features; bug fixes only (but see items 3 and 4). Feature development is for a future separate branch.
- No major rewrites. No refactoring code that is not fully understood.
- No changes in documented behaviour, except if required for compliance with the POSIX shell language standard which David Korn intended for ksh to follow.
- No 100% bug compatibility. Broken and undocumented behaviour gets fixed.
- No bureaucracy, no formalities. Just fix it, or report it: create issues, send pull requests. Every interested party is invited to contribute.
- To help increase everyone's understanding of this code base, fixes and significant changes should be fully documented in commit messages.
Why?
Between 2017 and 2020 there was an ultimately unsuccessful attempt to breathe new life into the KornShell by extensively refactoring the last unstable AST beta version (93v-). While that ksh2020 branch is now abandoned and still has many critical bugs, it also had a lot of bugs fixed. More importantly, the AST issue tracker now contains a lot of documentation on how to fix those bugs, which makes it possible to backport many of them to the last stable release instead.
In February 2020, having concluded the AST 93v- beta was too broken to base new work on, others decided to start a new fork based on the last stable 93u+ 2012-08-01 release. Unfortunately, as of June 2020, the new ksh-community organisation is yet to see any significant activity four months after its bootstrapping. I hope that will change; I am ready to join efforts with them at any time, as well as anyone else who wants to contribute.
The last stable ksh93 release from 2012 is the least buggy release currently available, but it still has many serious bugs. So it is well past time to start fixing those bugs, leave the rest of the code alone, and get an improved release out there.
Build
After cloning this repo, cd to the top directory of it and run:
bin/package make
If you have trouble or want to tune the binaries, you may pass additional compiler and linker flags by appending it to the command shown above. E.g.:
bin/package make \
SHELL=/bin/bash CCFLAGS="-xc99 -D_XPG6 -m64 -xO4" LDFLAGS="-m64"
For more information run
bin/package help
Many other commands in this repo self-document via the --help, --man and
--html options; those that do have no separate manual page.
Test
After compiling, you can run the regression tests. Start by reading the information printed by:
bin/shtests --man
What is ksh93?
The following is the official AT&T description from 1993 that came with the ast-open distribution. The text is original, but hyperlinks were added here.
KSH-93 is the most recent version of the KornShell Language described in "The KornShell Command and Programming Language," by Morris Bolsky and David Korn of AT&T Bell Laboratories, ISBN 0-13-182700-6. The KornShell is a shell programming language, which is upward compatible with "sh" (the Bourne Shell), and is intended to conform to the IEEE P1003.2/ISO 9945.2 Shell and Utilities standard. KSH-93 provides an enhanced programming environment in addition to the major command-entry features of the BSD shell "csh". With KSH-93, medium-sized programming tasks can be performed at shell-level without a significant loss in performance. In addition, "sh" scripts can be run on KSH-93 without modification.
The code should conform to the IEEE POSIX 1003.1 standard and to the proposed ANSI-C standard so that it should be portable to all such systems. Like the previous version, KSH-88, it is designed to accept eight bit character sets transparently, thereby making it internationally compatible. It can support multi-byte characters sets with some characteristics of the character set given at run time.
KSH-93 provides the following features, many of which were also inherent in KSH-88:
- Enhanced Command Re-entry Capability: The KSH-93 history function records commands entered at any shell level and stores them, up to a user-specified limit, even after you log off. This allows you to re-enter long commands with a few keystrokes - even those commands you entered yesterday. The history file allows for eight bit characters in commands and supports essentially unlimited size histories.
- In-line Editing: In "sh", the only way to fix mistyped commands is to backspace or retype the line. KSH-93 allows you to edit a command line using a choice of EMACS-TC or "vi" functions. You can use the in-line editors to complete filenames as you type them. You may also use this editing feature when entering command lines from your history file. A user can capture keystrokes and rebind keys to customize the editing interface.
- Extended I/O Capabilities: KSH-93 provides several I/O capabilities not
available in "sh", including the ability to:
- specify a file descriptor for input and output
- start up and run co-processes
- produce a prompt at the terminal before a read
- easily format and interpret responses to a menu
- echo lines exactly as output without escape processing
- format output using printf formats.
- read and echo lines ending in "\".
- Improved performance: KSH-93 executes many scripts faster than the System V Bourne shell. A major reason for this is that many of the standard utilities are built-in. To reduce the time to initiate a command, KSH-93 allows commands to be added as built-ins at run time on systems that support dynamic loading such as System V Release 4.
- Arithmetic: KSH-93 allows you to do integer arithmetic in any base from two to sixty-four. You can also do double precision floating point arithmetic. Almost the complete set of C language operators are available with the same syntax and precedence. Arithmetic expressions can be used to as an argument expansion or as a separate command. In addition there is an arithmetic for command that works like the for statement in C.
- Arrays: KSH-93 supports both indexed and associative arrays. The subscript for an indexed array is an arithmetic expression, whereas, the subscript for an associative array is a string.
- Shell Functions and Aliases: Two mechanisms - functions and aliases - can be used to assign a user-selected identifier to an existing command or shell script. Functions allow local variables and provide scoping for exception handling. Functions can be searched for and loaded on first reference the way scripts are.
- Substring Capabilities: KSH-93 allows you to create a substring of any given string either by specifying the starting offset and length, or by stripping off leading or trailing substrings during parameter substitution. You can also specify attributes, such as upper and lower case, field width, and justification to shell variables.
- More pattern matching capabilities: KSH-93 allows you to specify extended regular expressions for file and string matches.
- KSH-93 uses a hierarchal name space for variables. Compound variables can be defined and variables can be passed by reference. In addition, each variable can have one or more disciplines associated with it to intercept assignments and references.
- Improved debugging: KSH-93 can generate line numbers on execution traces. Also, I/O redirections are now traced. There is a DEBUG trap that gets evaluated before each command so that errors can be localized.
- Job Control: On systems that support job control, including System V Release 4, KSH-93 provides a job-control mechanism almost identical to that of the BSD "csh", version 4.1. This feature allows you to stop and restart programs, and to move programs between the foreground and the background.
- Added security: KSH-93 can execute scripts which do not have read permission and scripts which have the setuid and/or setgid set when invoked by name, rather than as an argument to the shell. It is possible to log or control the execution of setuid and/or setgid scripts. The noclobber option prevents you from accidentally erasing a file by redirecting to an existing file.
- KSH-93 can be extended by adding built-in commands at run time. In addition, KSH-93 can be used as a library that can be embedded into an application to allow scripting.
Documentation for KSH-93 consists of an "Introduction to KSH-93", "Compatibility with the Bourne Shell" and a manual page and a README file. In addition, the "New KornShell Command and Programming Language" book is available from Prentice Hall.