initial import of bash 4.1

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+Compatibility with previous versions
+====================================
+
+This document details the incompatibilities between this version of bash,
+bash-4.1, and the previous widely-available versions, bash-2.x (which is
+still the `standard' version for a few Linux distributions) and bash-3.x. 
+These were discovered by users of bash-2.x and 3.x, so this list is not
+comprehensive.  Some of these incompatibilities occur between the current
+version and versions 2.0 and above.
+
+1.  Bash uses a new quoting syntax, $"...", to do locale-specific
+    string translation.  Users who have relied on the (undocumented)
+    behavior of bash-1.14 will have to change their scripts.  For
+    instance, if you are doing something like this to get the value of
+    a variable whose name is the value of a second variable:
+
+	eval var2=$"$var1"
+
+    you will have to change to a different syntax.
+
+    This capability is directly supported by bash-2.0:
+
+	var2=${!var1}
+
+    This alternate syntax will work portably between bash-1.14 and bash-2.0:
+
+	eval var2=\$${var1}
+
+2.  One of the bugs fixed in the YACC grammar tightens up the rules
+    concerning group commands ( {...} ).  The `list' that composes the
+    body of the group command must be terminated by a newline or
+    semicolon.  That's because the braces are reserved words, and are
+    recognized as such only when a reserved word is legal.  This means
+    that while bash-1.14 accepted shell function definitions like this:
+
+	foo() { : }
+
+    bash-2.0 requires this:
+
+	foo() { :; }
+
+    This is also an issue for commands like this:
+
+	mkdir dir || { echo 'could not mkdir' ; exit 1; }
+
+    The syntax required by bash-2.0 is also accepted by bash-1.14.
+
+3.  The options to `bind' have changed to make them more consistent with
+    the rest of the bash builtins.  If you are using `bind -d' to list
+    the readline key bindings in a form that can be re-read, use `bind -p'
+    instead.  If you were using `bind -v' to list the key bindings, use
+    `bind -P' instead.
+
+4.  The `long' invocation options must now be prefixed by `--' instead
+    of `-'.  (The old form is still accepted, for the time being.)
+
+5.  There was a bug in the version of readline distributed with bash-1.14
+    that caused it to write badly-formatted key bindings when using 
+    `bind -d'.  The only key sequences that were affected are C-\ (which
+    should appear as \C-\\ in a key binding) and C-" (which should appear
+    as \C-\").  If these key sequences appear in your inputrc, as, for
+    example,
+
+	"\C-\": self-insert
+
+    they will need to be changed to something like the following:
+
+	"\C-\\": self-insert
+
+6.  A number of people complained about having to use ESC to terminate an
+    incremental search, and asked for an alternate mechanism.  Bash-2.03
+    uses the value of the settable readline variable `isearch-terminators'
+    to decide which characters should terminate an incremental search.  If
+    that variable has not been set, ESC and Control-J will terminate a
+    search.
+
+7.  Some variables have been removed:  MAIL_WARNING, notify, history_control,
+    command_oriented_history, glob_dot_filenames, allow_null_glob_expansion,
+    nolinks, hostname_completion_file, noclobber, no_exit_on_failed_exec, and
+    cdable_vars.  Most of them are now implemented with the new `shopt'
+    builtin; others were already implemented by `set'.  Here is a list of
+    correspondences:
+
+	MAIL_WARNING			shopt mailwarn
+	notify				set -o notify
+	history_control			HISTCONTROL
+	command_oriented_history	shopt cmdhist
+	glob_dot_filenames		shopt dotglob
+	allow_null_glob_expansion	shopt nullglob
+	nolinks				set -o physical
+	hostname_completion_file	HOSTFILE
+	noclobber			set -o noclobber
+	no_exit_on_failed_exec		shopt execfail
+	cdable_vars			shopt cdable_vars
+
+8. `ulimit' now sets both hard and soft limits and reports the soft limit
+    by default (when neither -H nor -S is specified).  This is compatible
+    with versions of sh and ksh that implement `ulimit'.  The bash-1.14
+    behavior of, for example,
+
+		ulimit -c 0
+
+    can be obtained with
+
+		ulimit -S -c 0
+
+    It may be useful to define an alias:
+
+		alias ulimit="ulimit -S"
+
+9.  Bash-2.01 uses a new quoting syntax, $'...' to do ANSI-C string
+    translation.  Backslash-escaped characters in ... are expanded and
+    replaced as specified by the ANSI C standard.
+
+10. The sourcing of startup files has changed somewhat.  This is explained
+    more completely in the INVOCATION section of the manual page.
+
+    A non-interactive shell not named `sh' and not in posix mode reads
+    and executes commands from the file named by $BASH_ENV.  A
+    non-interactive shell started by `su' and not in posix mode will read
+    startup files.  No other non-interactive shells read any startup files.
+
+    An interactive shell started in posix mode reads and executes commands
+    from the file named by $ENV.
+
+11. The <> redirection operator was changed to conform to the POSIX.2 spec.
+    In the absence of any file descriptor specification preceding the `<>',
+    file descriptor 0 is used.  In bash-1.14, this was the behavior only
+    when in POSIX mode.  The bash-1.14 behavior may be obtained with
+
+	<>filename 1>&0
+
+12. The `alias' builtin now checks for invalid options and takes a `-p'
+    option to display output in POSIX mode.  If you have old aliases beginning
+    with `-' or `+', you will have to add the `--' to the alias command
+    that declares them:
+
+	alias -x='chmod a-x' --> alias -- -x='chmod a-x'
+
+13. The behavior of range specificiers within bracket matching expressions
+    in the pattern matcher (e.g., [A-Z]) depends on the current locale,
+    specifically the value of the LC_COLLATE environment variable.  Setting
+    this variable to C or POSIX will result in the traditional ASCII behavior
+    for range comparisons.  If the locale is set to something else, e.g.,
+    en_US (specified by the LANG or LC_ALL variables), collation order is
+    locale-dependent.  For example, the en_US locale sorts the upper and
+    lower case letters like this:
+
+	AaBb...Zz
+
+    so a range specification like [A-Z] will match every letter except `z'.
+    Other locales collate like
+
+        aAbBcC...zZ
+
+    which means that [A-Z] matches every letter except `a'.
+
+    The portable way to specify upper case letters is [:upper:] instead of
+    A-Z; lower case may be specified as [:lower:] instead of a-z.
+
+    Look at the manual pages for setlocale(3), strcoll(3), and, if it is
+    present, locale(1).
+
+    You can find your current locale information by running locale(1):
+
+	caleb.ins.cwru.edu(2)$ locale
+	LANG=en_US
+	LC_CTYPE="en_US"
+	LC_NUMERIC="en_US"
+	LC_TIME="en_US"
+	LC_COLLATE="en_US"
+	LC_MONETARY="en_US"
+	LC_MESSAGES="en_US"
+	LC_ALL=en_US
+
+    My advice is to put
+
+	export LC_COLLATE=C
+
+    into /etc/profile and inspect any shell scripts run from cron for
+    constructs like [A-Z].  This will prevent things like
+
+	rm [A-Z]*
+
+    from removing every file in the current directory except those beginning
+    with `z' and still allow individual users to change the collation order.
+    Users may put the above command into their own profiles as well, of course.
+
+14. Bash versions up to 1.14.7 included an undocumented `-l' operator to
+    the `test/[' builtin.  It was a unary operator that expanded to the
+    length of its string argument.  This let you do things like
+
+	test -l $variable -lt 20
+
+    for example.
+
+    This was included for backwards compatibility with old versions of the
+    Bourne shell, which did not provide an easy way to obtain the length of
+    the value of a shell variable.
+
+    This operator is not part of the POSIX standard, because one can (and
+    should) use ${#variable} to get the length of a variable's value.
+    Bash-2.x does not support it.
+
+15. Bash no longer auto-exports the HOME, PATH, SHELL, TERM, HOSTNAME,
+    HOSTTYPE, MACHTYPE, or OSTYPE variables.  If they appear in the initial
+    environment, the export attribute will be set, but if bash provides a
+    default value, they will remain local to the current shell.
+
+16. Bash no longer initializes the FUNCNAME, GROUPS, or DIRSTACK variables
+    to have special behavior if they appear in the initial environment.
+
+17. Bash no longer removes the export attribute from the SSH_CLIENT or
+    SSH2_CLIENT variables, and no longer attempts to discover whether or
+    not it has been invoked by sshd in order to run the startup files.
+
+18. Bash no longer requires that the body of a function be a group command;
+    any compound command is accepted.
+
+19. As of bash-3.0, the pattern substitution operators no longer perform
+    quote removal on the pattern before attempting the match.  This is the
+    way the pattern removal functions behave, and is more consistent.
+
+20. After bash-3.0 was released, I reimplemented tilde expansion, incorporating
+    it into the mainline word expansion code.  This fixes the bug that caused
+    the results of tilde expansion to be re-expanded.  There is one
+    incompatibility:  a ${paramOPword} expansion within double quotes will not
+    perform tilde expansion on WORD.  This is consistent with the other
+    expansions, and what POSIX specifies.
+
+21. A number of variables have the integer attribute by default, so the +=
+    assignment operator returns expected results: RANDOM, LINENO, MAILCHECK,
+    HISTCMD, OPTIND.
+
+22. Bash-3.x is much stricter about $LINENO correctly reflecting the line
+    number in a script; assignments to LINENO have little effect.
+
+23. By default, readline binds the terminal special characters to their
+    readline equivalents.  As of bash-3.1/readline-5.1, this is optional and
+    controlled by the bind-tty-special-chars readline variable.
+
+24. The \W prompt string expansion abbreviates $HOME as `~'.  The previous
+    behavior is available with ${PWD##/*/}.
+
+25. The arithmetic exponentiation operator is right-associative as of bash-3.1.
+
+26. The rules concerning valid alias names are stricter, as per POSIX.2.
+
+27. The Readline key binding functions now obey the convert-meta setting active
+    when the binding takes place, as the dispatch code does when characters
+    are read and processed.
+
+28. The historical behavior of `trap' reverting signal disposition to the
+    original handling in the absence of a valid first argument is implemented
+    only if the first argument is a valid signal number.
+
+29. In versions of bash after 3.1, the ${parameter//pattern/replacement}
+    expansion does not interpret `%' or `#' specially.  Those anchors don't
+    have any real meaning when replacing every match.
+
+30. Beginning with bash-3.1, the combination of posix mode and enabling the
+    `xpg_echo' option causes echo to ignore all options, not looking for `-n'
+
+31. Beginning with bash-3.2, bash follows the Bourne-shell-style (and POSIX-
+    style) rules for parsing the contents of old-style backquoted command
+    substitutions.  Previous versions of bash attempted to recursively parse
+    embedded quoted strings and shell constructs; bash-3.2 uses strict POSIX
+    rules to find the closing backquote and simply passes the contents of the
+    command substitution to a subshell for parsing and execution.
+
+32. Beginning with bash-3.2, bash uses access(2) when executing primaries for
+    the test builtin and the [[ compound command, rather than looking at the
+    file permission bits obtained with stat(2).  This obeys restrictions of
+    the file system (e.g., read-only or noexec mounts) not available via stat.
+
+33. Bash-3.2 adopts the convention used by other string and pattern matching
+    operators for the `[[' compound command, and matches any quoted portion
+    of the right-hand-side argument to the =~ operator as a string rather
+    than a regular expression.
+
+34. Bash-4.0 allows the behavior in the previous item to be modified using
+    the notion of a shell `compatibility level'.  If the compat31 shopt
+    option is set, quoting the pattern has no special effect.
+
+35. Bash-3.2 (patched) and Bash-4.0 fix a bug that leaves the shell in an
+    inconsistent internal state following an assignment error.  One of the
+    changes means that compound commands or { ... } grouping commands are
+    aborted under some circumstances in which they previously were not.
+    This is what Posix specifies.
+
+36. Bash-4.0 now allows process substitution constructs to pass unchanged
+    through brace expansion, so any expansion of the contents will have to be
+    separately specified, and each process subsitution will have to be
+    separately entered.
+
+37. Bash-4.0 now allows SIGCHLD to interrupt the wait builtin, as Posix
+    specifies, so the SIGCHLD trap is no longer always invoked once per
+    exiting child if you are using `wait' to wait for all children.
+
+38. Since bash-4.0 now follows Posix rules for finding the closing delimiter
+    of a $() command substitution, it will not behave as previous versions
+    did, but will catch more syntax and parsing errors before spawning a
+    subshell to evaluate the command substitution.
+
+39. The programmable completion code uses the same set of delimiting characters
+    as readline when breaking the command line into words, rather than the
+    set of shell metacharacters, so programmable completion and readline
+    should be more consistent.
+
+40. When the read builtin times out, it attempts to assign any input read to
+    specified variables, which also causes variables to be set to the empty
+    string if there is not enough input.  Previous versions discarded the
+    characters read.
+
+41. Beginning with bash-4.0, when one of the commands in a pipeline is killed
+    by a SIGINT while executing a command list, the shell acts as if it
+    received the interrupt.  This can be disabled by setting the compat31 or
+    compat32 shell options.
+
+42. Bash-4.0 changes the handling of the set -e option so that the shell exits
+    if a pipeline fails (and not just if the last command in the failing
+    pipeline is a simple command).  This is not as Posix specifies.  There is
+    work underway to update this portion of the standard; the bash-4.0
+    behavior attempts to capture the consensus at the time of release.
+
+43. Bash-4.0 fixes a Posix mode bug that caused the . (source) builtin to
+    search the current directory for its filename argument, even if "." is
+    not in $PATH.  Posix says that the shell shouldn't look in $PWD in this
+    case.
+
+44. Bash-4.1 uses the current locale when comparing strings using the < and
+    > operators to the `[[' command.  This can be reverted to the previous
+    behavior by setting one of the `compatNN' shopt options.
+
+Shell Compatibility Level
+=========================
+
+Bash-4.0 introduced the concept of a `shell compatibility level', specified
+as a set of options to the shopt builtin (compat31, compat32, compat40 at
+this writing).  There is only one current compatibility level -- each
+option is mutually exclusive.  This list does not mention behavior that is
+standard for a particular version (e.g., setting compat32 means that quoting
+the rhs of the regexp matching operator quotes special regexp characters in
+the word, which is default behavior in bash-3.2 and above).
+
+compat31 set
+	- the < and > operators to the [[ command do not consider the current
+	  locale when comparing strings
+	- quoting the rhs of the regexp matching operator (=~) has no
+	  special effect
+
+compat32 set
+	- the < and > operators to the [[ command do not consider the current
+	  locale when comparing strings
+
+compat40 set
+	- the < and > operators to the [[ command do not consider the current
+	  locale when comparing strings
+	- interrupting a command list such as "a ; b ; c" causes the execution
+	  of the entire list to be aborted
+
+-------------------------------------------------------------------------------
+
+Copying and distribution of this file, with or without modification,
+are permitted in any medium without royalty provided the copyright
+notice and this notice are preserved.  This file is offered as-is,
+without any warranty.