Ash (Almquist Shell) Variants

2006-30-01 (see recent changes)

This list aims at documenting relationships. Thus, characteristic changes or bugfixes are listed, chosen somewhat arbitrarily. For the variants without any changelogs (traditional BSDs and Minix) this log tries to be complete. For the other variants this was certainly not the goal.

Content:

• 1. Original release
• 2. Traditional BSDs (4.3BSD-Net/2, 4.4BSD-Alpha, 4.4BSD-Lite, 4.4BSD-Lite2)
• 3. NetBSD
• 4. FreeBSD
• 5. BSD/OS (BSDi)
• 6. dash
• 7. BusyBox
• 8. Minix

1.) Original release ('89)

Some differences to the SVR4 shell (which were never changed later):

• implements "$(...)" command substitution
• accepts "export VAR=value"

Some details, where the original ash resembles the SVR4 shell, but which were changed in the modern variants:

• no command line editing and history (by intention)
• parameter expansion doesn't know # and %
• read doesn't know "-r"
• no arithmetic expansion
• traditional behaviour about IFS vs. "$*"

As summary in advance: some details which are only found in the original (and early traditional BSD) variants.

• doesn't accept nested back-ticks (accidentally)
• undocumented: no "type" built-in (accidentally)
• flag "v" not implemented
• "for i do" not accepted
• reads SHINIT at start (except if a login shell or called with "sh file")
• "trap" doesn't accept symbolic signal names
• SEGV on "${var=`cmd`}"
• rejecting "case x in (x)" ^[1] also might fit here, but NetBSD and Minix behave as well.
• negation of patternmatching with "!!pattern"
• flag z (don't leave pattern after redirection unchanged if it doesn't match)

For some more differences to the SVR4 shell, see DIFFERENCES from the distribution.
Naturally, nothing from the list of Bourne specific features is implemented.

2.) Traditional BSDs

  4.3BSD-Net/2 (06/91)

• Not only "--", but also "-" terminates options
• PS1 depends on uid
• compile time option for different parsing in eval
• undocumented: flag v becomes a synonym for x
• "chdir" becomes synonym for "cd"
• built-in "bltin" renamed to "command"
• built-ins "catf", "expr", "line", "nlecho" removed
• job control fixed, formerly only 4 jobs were handled properly (Almquist himself subsequently had filed a patch)
• A user without HOME starts in /tmp instead of / (except uid 0).

  4.4BSD-Alpha (06/92) - starts aiming at POSIX.2

• history and line editing (fc, $FCEDIT, $HISTSIZE, flags E and V)
• ...and atty support removed (optional support by terminal driver)
• arithmetic expansion "$((...))"
• built-in "printf"
• negation of pipeline with !
• tilde expansion added, /u/logname mechanism removed
• aliases
• reads ENV instead of SHINIT at start
• "set -o" prints options
• "cd -" added
• jobcontrol: flag j renamed to m (like SVR4 shell),
  flags C (noclobber), a (allexport), b (notify asynchronous jobs), u (error on unset) added,
  flag z removed
• warning "You have stopped jobs."
• "shift" built-in knows "can't shift that many"
• warning "running as root with dot in PATH" in case
• negation of patternmatching with "!!pattern" removed
• manual rewritten

  4.4BSD-Lite ('94)

   Apparently, the 386BSD cluster patch went into this release or was inspired by it:

• accepts nested back-ticks
• accepts "for i do"
• redirections may precede non-simple commands
• do not redirect STDIN of background commands to /dev/null if it has been redirected previously
• backquoted commands set $?

• "wait" yields an exit status
• "fc" knows "missing history argument"
• handles the empty command like other simple commands, allows "if ; [...]"

  4.4BSD-Lite2 ('95)

• parameter expansion knows # and %
• "ulimit" built-in
• arithmetic expansion accepts binary logic operators (&, |, ^, ~)
• "umask" understands symbolic notation
• PATH assigment preceding a command is even regarded for the lookup
• source command does path lookup for executable files
• doesn't warn root anymore if PATH contains a dot
• Only look up ENV at startup if IDs equal effective IDs
• "false" built-in added ("true" already was handled equal to ":")
• dash can be escaped in range, like [a\-z]
• empty command, e.g. "if ; [...]", not allowed anymore

3.) NetBSD sh

• "umask" accepts symbolic notation, 07/93, NetBSD 1.0
• "ulimit" built-in, 11/94, NetBSD 1.2
• # and % parameter expansion, 01/95, NetBSD 1.2
• "type" built-in added, 02/97, NetBSD 1.3
• "read -r", 11/97, NetBSD 1.3
• "trap" accepts symbolic names (and more fixes), 03/01, NetBSD 1.6

• does not accept "case x in (x)" until the time of this writing (NetBSD 3.0) ^[1]

• "${x-a b c}" expands to several arguments, 06/04, NetBSD 3
• todo: modern behaviour about IFS vs. "$*"

CVS-Web on netbsd.org.

4.) FreeBSD sh

• "trap" accepts symbolic names, 12/96, FreeBSD 2.2
• [^...] negation,   6/97, FreeBSD 2.2
• "read -r",   09/99, FreeBSD 3.3
• "var=x eval echo \$var" prints x,   05/00, FreeBSD 4.4
• accepts "case x in (x)",   10/02, FreeBSD 4.8/5.3

• doesn't expand "${x-a b c}" to several arguments

• todo: modern behaviour about IFS vs. "$*"

CVS-Web on freebsd.org.

5.) BSD/OS 4.2 sh (BSDi) ('97)

• accepts "case x in (x)"
• additionally contains the SCCS-ID: "$NetBSD: tokenizer.c,v 1.2 1997/01/11 06:48:15 lukem Exp $"

• no "read -r"
• no "type" built-in
• "trap" doesn't accept symbolic names
• old behaviour about IFS vs. "$*"

6.) dash ('97-)

• accepts "case x in (x)" since 08/99, 0.3.5-4
• substituted the embedded pmatch() with fnmatch(3) as of 0.3.7-1, then switched several times and kept pmatch() since 0.4.26-1 (problems due to several bugs in some glibc versions).

• todo: change of ${x-a b c}

Home of dash, Debian package. For the changelogs, see ./Changelog and the older ./debian/changelog in the distribution.

7.) BusyBox ash ('01-)

• compile time options to deactivate jobcontrol and several built-ins (alias, type, getopts, command, true, false, chdir).
• undocumented: calls fnmatch(3) instead of the embedded pmatch(), which is problematic due to bugs in some glibc versions. This also introduces [^...] as synonym for [!...].

8.) Minix sh ('01)

Derived from 4.3BSD-Net/2, according to the SCCS-IDs,
apparently with the 386bsd cluster patch applied.

Additionally:

• knows tilde expansion
• "-" is also end of options
• getopts fixed (OPTIND correct after an "option requires an argument")
• accepts empty command, e.g. "if ; [...]"
• "false" built-in added (true was always a synonym for the colon command)
• Command line editing and history added by means of Minix readline()

• shell doesn't read file after exec failed. Hence, shell scripts require #!
• prompt reflects exit status of last command: # if 0, * otherwise
• job control disabled
• reads $HOME/.ashrc or $HOME/.profile, respectively

• no # and % parameter expansion
• no arithmetic expansion
• no negation of pipeline with !
• no ulimit
• doesn't accept "case x in (x)"
• doesn't implement "read -r"
• doesn't implement "cd -"
• old behavour about "IFS vs. $*"