Image of Operating System Concepts
Image of Modern Operating Systems (3rd Edition)
Image of Advanced Programming in the UNIX Environment, Second Edition (Addison-Wesley Professional Computing Series)
Image of RHCE Red Hat Certified Engineer Linux Study Guide (Exam RH302) (Certification Press)

The KSH93 Version String

Korn Shell 93 (ksh93) is somewhat unusual in that it has a non-intuitive release versioning scheme, and it’s version string contains more than simply a version number or date.

There are a number of ways of obtaining version information including the following:

$ echo ${.sh.version}
Version AJM 93v- 2014-12-24
$ echo $KSH_VERSION           
Version AJM 93v- 2014-12-24
$ set -o vi
(Press ESC followed by Ctrl-V)
$ Version AJM 93v- 2014-12-24

KSH_VERSION was not available in ksh93 prior to version 93t(2008) and is actually implemented as a name reference (nameref) to the .sh.version compound shell variable.

$ echo ${!KSH_VERSION}

The release version and date is defined in the …/cmd/ksh93/include/version.h header file as a string:

$ cat version.h
 *                                                                      *
 *               This software is part of the ast package               *
 *          Copyright (c) 1982-2015 AT&T Intellectual Property          *
 *                      and is licensed under the                       *
 *                 Eclipse Public License, Version 1.0                  *
 *                    by AT&T Intellectual Property                     *
 *                                                                      *
 *                A copy of the License is available at                 *
 *           *
 *         (with md5 checksum b35adb5213ca9657e911e9befb180842)         *
 *                                                                      *
 *              Information and Software Systems Research               *
 *                            AT&T Research                             *
 *                           Florham Park NJ                            *
 *                                                                      *
 *                    David Korn <dgkorn>                    *
 *                                                                      *
#define SH_RELEASE "93v- 2014-12-24"

As you can see version.h only contains part of the version string. So how is the full version string that you see build up?

From …/cmd/ksh93/sh/init.c:

#include        "version.h"
char e_version[] =
    "\n@(#)$Id: Version "
#define ATTRS 1
#define ATTRS 1
#define ATTRS 1
#define ATTRS 1
#define ATTRS 1
#define ATTRS 1
#if SHOPT_PFSH && _hdr_exec_attr
#define ATTRS 1
#define ATTRS 1
    " "
    SH_RELEASE " $\0\n";

Aa you can see from the above code snippets, the actual version string emitted by the shell contains a number of bits of useful information.

  • Specific enabled compile time options such as coshell (J) or audit (A) support
  • The string 93 followed by a single lowercase letter such as u or v designating a specific major release, followed by an optional minus () or plus (+) symbol
  • Date string in the format YYYY-MM-DD

The major release letter is rarely incremented. A major release does not have a minus () or plus (+) symbol appended to the release letter. A minus () appended to the release string indicates that the release is either an alpha or beta release of ksh93 with the exact version of the alpha or beta release being designated by the date. A plus (+) appended to the release string indicates that the release is a bug fix or minor enhancement release of ksh93 with the exact version of the release being designated by the date.

Looking at the ksh93 source code, it appears that the release date is used to actually distinguish between various releases when necessary – not the release letter. In fact, there is specific code in …/cmd/ksh93/sh/init.c in the form of a get discipline function to simplify retrieving the release date.

static Sfdouble_t nget_version(Namval_t *np, Namfun_t *fp) {
    const char *cp = e_version + strlen(e_version) - 10;
    int c;
    Sflong_t t = 0;

    while ((c = *cp++)) {
        if (c >= '0' && c < = '9') {
            t *= 10;
            t += c - '0';
    return (Sfdouble_t)t;

static const Namdisc_t SH_VERSION_disc = {0, 0, get_version, nget_version};

This code enables you to do the following:

$ echo $(( .sh.version ))
$ echo $(( KSH_VERSION ))

You can also do more exotic things with the release string as shown in the following trivial use of the alarm builtin.

$ alarm -r version +5
$ function version.alarm { print -n "$(echo -n "${.sh.version} "; date +%H:%S)\r"; }
$ read dummy

The first line specifies that the function named version is to be invoked every 5 seconds. The second line defines the actual function i.e. print the version string followed by the current time in HH:SS format. The third line is just a hack so that you can see the results of the previous 2 lines.

Currently there is what I would consider a significant flaw in ksh93 regarding the name reference to .sh.version, i.e. the version string, The problem is that KSH_VERSION it is not marked readonly and can be overwritten. This means that ksh93 scripts that reply on a particular value of KSH_VERSION can be fooled.

$ echo $KSH_VERSION           
Version AJM 93v- 2014-12-24


This cannot occur with pdksh and derived shells where KSH_VERSION is a readonly shell variable.


Comments are closed.