Here-documents within $(...) command substitutions may once more be
delimited by the closing right paren, instead of requiring a newline.
Bash's file status checks (executable, readable, etc.) now take file
system ACLs into account on file systems that support them.
Bash now passes environment variables with names that are not valid
shell variable names through into the environment passed to child
processes.
The `execute-unix-command' readline function now attempts to clear and
reuse the current line rather than move to a new one after the command
executes.
`printf -v' can now assign values to array indices.
New `complete -E' and `compopt -E' options that work on the "empty"
completion: completion attempted on an empty command line.
New complete/compgen/compopt -D option to define a `default' completion:
a completion to be invoked on command for which no completion has been
defined. If this function returns 124, programmable completion is
attempted again, allowing a user to dynamically build a set of completions
as completion is attempted by having the default completion function
install individual completion functions each time it is invoked.
When displaying associative arrays, subscripts are now quoted.
Changes to dabbrev-expand to make it more `emacs-like': no space appended
after matches, completions are not sorted, and most recent history entries
are presented first.
The [[ and (( commands are now subject to the setting of `set -e' and the
ERR trap.
The source/. builtin now removes NUL bytes from the file before attempting
to parse commands.
There is a new configuration option (in config-top.h) that forces bash to
forward all history entries to syslog.
A new variable $BASHOPTS to export shell options settable using `shopt' to
child processes.
There is a new confgure option that forces the extglob option to be
enabled by default.
New variable $BASH_XTRACEFD; when set to an integer bash will write xtrace
output to that file descriptor.
If the optional left-hand-side of a redirection is of the form {var}, the
shell assigns the file descriptor used to $var or uses $var as the file
descriptor to move or close, depending on the redirection operator.
The < and > operators to the [[ conditional command now do string
comparison according to the current locale if the compatibility level
is greater than 40.
Programmable completion now uses the completion for `b' instead of `a'
when completion is attempted on a line like: a $(b c.
Force extglob on temporarily when parsing the pattern argument to
the == and != operators to the [[ command, for compatibility.
Changed the behavior of interrupting the wait builtin when a SIGCHLD is
received and a trap on SIGCHLD is set to be Posix-mode only.
The read builtin has a new `-N nchars' option, which reads exactly NCHARS
characters, ignoring delimiters like newline.
The mapfile/readarray builtin no longer stores the commands it invokes via
callbacks in the history list.
There is a new `compat40' shopt option.
