Normally, suspending a login shell with SIGSTOP (e.g., kill -STOP $$) will irrecoverably freeze the terminal session, so it is a good idea to prohibit that. But job_kill() (called via the 'kill' built-in, b_kill()) assumes that any login shell has a parent PID of 1, a.k.a. init. This may have been valid on some systems back in the 1980s, but when people started using graphical terminals (if not before), that assumption became universally bogus. Some shells (at least yash) prohibit issuing SIGSTOP to self if their process is the session leader. But even that doesn't always hold. For instance, on macOS, the terminal creates a login(1) process (the session leader), and the login shell is its child. So really the only thing we can reliably do is check for the -l/--login/SH_LOGIN_SHELL shell option (as the 'suspend' built-in already does; see
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.
- Fixing bugs is main focus of the 1.0 series. Major feature development is for future versions (1.1 and up).
- No major rewrites. No refactoring code that is not fully understood.
- Maintain documented behaviour. Changes required for compliance with the
POSIX shell language standard
are implemented for the
posixmode only to avoid breaking legacy scripts.
- 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.
- Code style varies somewhat in this historic code base.
Your changes should match the style of the code surrounding them.
Indent with tabs, assuming an 8-space tab width.
Opening braces are on a line of their own, at the same indentation level
as their corresponding closing brace.
Comments always use
- Good judgment may override this policy.
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 effort 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 made it possible to backport many of them to the last stable release instead. This ksh 93u+m reboot now incorporates many of these bugfixes, plus patches from OpenSUSE, Red Hat, and Solaris, as well as many new fixes from the community (1, 2). Though there are many bugs left to fix, we are confident at this point that 93u+m is already the least buggy version of ksh93 ever released. As of late 2021, distributions such as Debian and Slackware have begun to package it as their default version of ksh93.
To build ksh with a custom configuration of features, edit
cd to the top directory and run:
To suppress compiler output, use
quiet make instead of
In some non-POSIX shells you might need to prepend
sh to all calls to
The compiled binaries are stored in the
arch directory, in a subdirectory
that corresponds to your architecture. The command
bin/package host type
outputs the name of this subdirectory.
If you have trouble or want to tune the binaries, you may pass additional
compiler and linker flags. It is usually best to export these as environment
variables before running
bin/package as they could change the name of
the build subdirectory of the
arch directory, so exporting them is a
convenient way to keep them consistent between build and test commands.
Note that this system uses
CCFLAGS instead of the usual
An example that makes Solaris Studio cc produce a 64-bit binary:
export CCFLAGS="-m64 -O" LDFLAGS="-m64" bin/package make
Alternatively you can append these to the command, and they will only be used for that command. You can also specify an alternative shell in which to run the build scripts this way. For example:
bin/package make SHELL=/bin/bash CCFLAGS="-O2 -I/opt/local/include" LDFLAGS="-L/opt/local/lib"
Note: Do not add compiler flags that cause the compiler to emit terminal
escape codes, such as
-fdiagnostics-color=always; this will cause the
build to fail as the probing code greps compiler diagnostics. Additionally,
do not add the
-ffast-math compiler flag; arithmetic bugs will occur when
using that flag.
For more information run
Many other commands in this repo self-document via the
--html options; those that do have no separate manual page.
After compiling, you can run the regression tests. To run the default test sets for ksh and the build system, use:
For ksh, use the
shtests command directly to control the regression test runs.
Start by reading the information printed by:
To hand-test ksh (as well as the utilities and the autoloadable functions that come with it) without installing, run:
bin/package install destination_directory [ command ... ]
Any command from the
arch directory can be installed. If no command is
shcomp are assumed.
The destination_directory is created if it does not exist. Commands are
installed in its
bin subdirectory and each command's manual page, if
available, is installed in
Destination directories with whitespace or shell pattern characters in their pathnames are not yet supported.
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 hierarchical 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.