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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.
+bash-4.3, and the previous widely-available versions, bash-3.x (which is
+still the `standard' version for Mac OS X), 4.0/4.1 (which are still
+standard on a few Linux distributions), and bash-4.2, the current
+widely-available version. These were discovered by users of bash-2.x
+through 4.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 (ASCII collating and strcmp(3)) by setting one of the
`compatNN' shopt options, where NN is less than 41.
-45. Command substitutions now remove the caller's trap strings when trap is
+45. Bash-4.1 conforms to the current Posix specification for `set -u':
+ expansions of $@ and $* when there are no positional parameters do not
+ cause the shell to exit.
+
+46. Bash-4.1 implements the current Posix specification for `set -e' and
+ exits when any command fails, not just a simple command or pipeline.
+
+47. Command substitutions now remove the caller's trap strings when trap is
run to set a new trap in the subshell. Previous to bash-4.2, the old
trap strings persisted even though the actual signal handlers were reset.
-46. When in Posix mode, a single quote is not treated specially in a
+48. When in Posix mode, a single quote is not treated specially in a
double-quoted ${...} expansion, unless the expansion operator is
# or % or the new `//', `^', or `,' expansions. In particular, it
does not define a new quoting context. This is from Posix interpretation
221.
-47. Posix mode shells no longer exit if a variable assignment error occurs
+49. Posix mode shells no longer exit if a variable assignment error occurs
with an assignment preceding a command that is not a special builtin.
+50. Bash-4.2 attempts to preserve what the user typed when performing word
+ completion, instead of, for instance, expanding shell variable
+ references to their value.
+
+51. When in Posix mode, bash-4.2 exits if the filename supplied as an argument
+ to `.' is not found and the shell is not interactive.
+
+52. When compiled for strict Posix compatibility, bash-4.3 does not enable
+ history expansion by default in interactive shells, since it results in
+ a non-conforming environment.
+
+53. Bash-4.3 runs the replacement string in the pattern substitution word
+ expansion through quote removal. The code already treats quote
+ characters in the replacement string as special; if it treats them as
+ special, then quote removal should remove them.
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, and
-compat41 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).
+as a set of options to the shopt builtin (compat31, compat32, compat40,
+compat41, and compat42 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).
+
+Bash-4.3 introduces a new shell variable: BASH_COMPAT. The value assigned
+to this variable (a decimal version number like 4.2, or an integer
+corresponding to the compatNN option, like 42) determines the compatibility
+level.
compat31 set
- the < and > operators to the [[ command do not consider the current
compat41 set
- interrupting a command list such as "a ; b ; c" causes the execution
- of the entire list to be aborted (in versions before bash-4.0,
+ of the entire list to be aborted (in versions before bash-4.1,
interrupting one command in a list caused the next to be executed)
- when in posix mode, single quotes in the `word' portion of a
double-quoted parameter expansion define a new quoting context and
are treated specially
+
+compat42 set
+ - the replacement string in double-quoted pattern substitution is not
+ run through quote removal, as in previous versions
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