Bash-4.2 distribution sources and documentation
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doc/FAQ
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doc/FAQ
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@ -1,4 +1,4 @@
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This is the Bash FAQ, version 4.11, for Bash version 4.1.
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This is the Bash FAQ, version 4.12, for Bash version 4.2.
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This document contains a set of frequently-asked questions concerning
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Bash, the GNU Bourne-Again Shell. Bash is a freely-available command
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@ -36,8 +36,8 @@ A10) What is the bash `posix mode'?
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Section B: The latest version
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B1) What's new in version 4.1?
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B2) Are there any user-visible incompatibilities between bash-4.1 and
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B1) What's new in version 4.2?
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B2) Are there any user-visible incompatibilities between bash-4.2 and
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previous bash versions?
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Section C: Differences from other Unix shells
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@ -144,26 +144,26 @@ of Case Western Reserve University.
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A2) What's the latest version?
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The latest version is 4.1, first made available on 31 December, 2009.
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The latest version is 4.2, first made available on 14 February, 2011.
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A3) Where can I get it?
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Bash is the GNU project's shell, and so is available from the
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master GNU archive site, ftp.gnu.org, and its mirrors. The
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latest version is also available for FTP from ftp.cwru.edu.
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The following URLs tell how to get version 4.1:
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The following URLs tell how to get version 4.2:
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ftp://ftp.gnu.org/pub/gnu/bash/bash-4.1.tar.gz
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ftp://ftp.cwru.edu/pub/bash/bash-4.1.tar.gz
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ftp://ftp.gnu.org/pub/gnu/bash/bash-4.2.tar.gz
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ftp://ftp.cwru.edu/pub/bash/bash-4.2.tar.gz
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Formatted versions of the documentation are available with the URLs:
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ftp://ftp.gnu.org/pub/gnu/bash/bash-doc-4.1.tar.gz
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ftp://ftp.cwru.edu/pub/bash/bash-doc-4.1.tar.gz
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ftp://ftp.gnu.org/pub/gnu/bash/bash-doc-4.2.tar.gz
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ftp://ftp.cwru.edu/pub/bash/bash-doc-4.2.tar.gz
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Any patches for the current version are available with the URL:
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ftp://ftp.cwru.edu/pub/bash/bash-4.1-patches/
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ftp://ftp.cwru.edu/pub/bash/bash-4.2-patches/
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A4) On what machines will bash run?
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@ -219,7 +219,7 @@ Mark began to work with bash-2.05, but I don't know the current status.
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Bash-3.0 compiles and runs with no modifications under Microsoft's Services
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for Unix (SFU), once known as Interix. I do not anticipate any problems
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with building bash-4.1, but will gladly accept any patches that are needed.
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with building bash-4.2, but will gladly accept any patches that are needed.
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A6) How can I build bash with gcc?
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@ -388,14 +388,88 @@ They are also listed in a section in the Bash Reference Manual
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Section B: The latest version
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B1) What's new in version 4.1?
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B1) What's new in version 4.2?
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Bash-4.1 is the first revision to the fourth major release of bash.
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Bash-4.2 is the second revision to the fourth major release of bash.
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Bash-4.1 contains the following new features (see the manual page for
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complete descriptions and the CHANGES and NEWS files in the bash-4.1
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Bash-4.2 contains the following new features (see the manual page for
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complete descriptions and the CHANGES and NEWS files in the bash-4.2
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distribution):
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o `exec -a foo' now sets $0 to `foo' in an executable shell script without a
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leading #!.
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o Subshells begun to execute command substitutions or run shell functions or
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builtins in subshells do not reset trap strings until a new trap is
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specified. This allows $(trap) to display the caller's traps and the
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trap strings to persist until a new trap is set.
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o `trap -p' will now show signals ignored at shell startup, though their
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disposition still cannot be modified.
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o $'...', echo, and printf understand \uXXXX and \UXXXXXXXX escape sequences.
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o declare/typeset has a new `-g' option, which creates variables in the
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global scope even when run in a shell function.
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o test/[/[[ have a new -v variable unary operator, which returns success if
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`variable' has been set.
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o Posix parsing changes to allow `! time command' and multiple consecutive
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instances of `!' (which toggle) and `time' (which have no cumulative
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effect).
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o Posix change to allow `time' as a command by itself to print the elapsed
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user, system, and real times for the shell and its children.
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o $((...)) is always parsed as an arithmetic expansion first, instead of as
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a potential nested command substitution, as Posix requires.
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o A new FUNCNEST variable to allow the user to control the maximum shell
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function nesting (recursive execution) level.
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o The mapfile builtin now supplies a third argument to the callback command:
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the line about to be assigned to the supplied array index.
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o The printf builtin has as new %(fmt)T specifier, which allows time values
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to use strftime-like formatting.
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o There is a new `compat41' shell option.
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o The cd builtin has a new Posix-mandated `-e' option.
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o Negative subscripts to indexed arrays, previously errors, now are treated
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as offsets from the maximum assigned index + 1.
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o Negative length specifications in the ${var:offset:length} expansion,
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previously errors, are now treated as offsets from the end of the variable.
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o Parsing change to allow `time -p --'.
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o Posix-mode parsing change to not recognize `time' as a keyword if the
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following token begins with a `-'. This means no more Posix-mode
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`time -p'. Posix interpretation 267.
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o There is a new `lastpipe' shell option that runs the last command of a
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pipeline in the current shell context. The lastpipe option has no
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effect if job control is enabled.
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o History expansion no longer expands the `$!' variable expansion.
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o Posix mode shells no longer exit if a variable assignment error occurs
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with an assignment preceding a command that is not a special builtin.
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o Non-interactive mode shells exit if -u is enabled an an attempt is made
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to use an unset variable with the % or # expansions, the `//', `^', or
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`,' expansions, or the parameter length expansion.
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o Posix-mode shells use the argument passed to `.' as-is if a $PATH search
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fails, effectively searching the current directory. Posix-2008 change.
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A short feature history dating back to Bash-2.0:
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Bash-4.1 contained the following new features:
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o Here-documents within $(...) command substitutions may once more be
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delimited by the closing right paren, instead of requiring a newline.
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@ -502,8 +576,6 @@ o New bindable readline variable: enable-meta-key. Controls whether or not
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readline sends the smm/rmm sequences if the terminal indicates it has a
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meta key that enables eight-bit characters.
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A short feature history dating from Bash-2.0:
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Bash-4.0 contained the following new features:
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o When using substring expansion on the positional parameters, a starting
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@ -901,14 +973,14 @@ grammar tighter and smaller (66 reduce-reduce conflicts gone)
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lots of code now smaller and faster
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test suite greatly expanded
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B2) Are there any user-visible incompatibilities between bash-4.1 and
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B2) Are there any user-visible incompatibilities between bash-4.2 and
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previous bash versions?
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There are a few incompatibilities between version 4.1 and previous
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There are a few incompatibilities between version 4.2 and previous
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versions. They are detailed in the file COMPAT in the bash distribution.
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That file is not meant to be all-encompassing; send mail to
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bash-maintainers@gnu.org (or bug-bash@gnu.org if you would like
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community discussion) if if you find something that's not mentioned there.
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community discussion) if you find something that's not mentioned there.
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Section C: Differences from other Unix shells
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@ -1118,7 +1190,7 @@ C3) Which new features in ksh-93 are not in bash, and which are?
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This list is current through ksh93t+ (05/05/2009)
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New things in ksh-93 not in bash-4.1:
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New things in ksh-93 not in bash-4.2:
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floating point arithmetic and variables
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math library functions
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${!name[sub]} name of subscript for associative array
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`fc' has been renamed to `hist'
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`.' can execute shell functions
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getopts -a
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printf %B, %H, %P, %R, %T, %Z modifiers, output base for %d, `=' flag
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printf %B, %H, %P, %R, %Z modifiers, output base for %d, `=' flag
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read -n/-N differ/-v
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set -o showme/-o multiline (bash default)
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`sleep' and `getconf' builtins (bash has loadable versions)
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@ -1148,16 +1220,14 @@ New things in ksh-93 not in bash-4.1:
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[[ -R name ]] (checks whether or not name is a nameref)
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typeset -C/-S/-T/-X/-h/-s
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experimental `type' definitions (a la typedef) using typeset
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negative subscripts for indexed array variables
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array expansions ${array[sub1..sub2]} and ${!array[sub1..sub2]}
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associative array assignments using `;' as element separator
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command substitution $(n<#) expands to current byte offset for fd N
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new '${ ' form of command substitution, executed in current shell
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new >;/<>;/<#pat/<##pat/<#/># redirections
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brace expansion printf-like formats
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[[ -v var ]] operators (checks whether or not var is set)
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New things in ksh-93 present in bash-4.1:
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New things in ksh-93 present in bash-4.2:
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associative arrays
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[n]<&word- and [n]>&word- redirections (combination dup and close)
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for (( expr1; expr2; expr3 )) ; do list; done - arithmetic for command
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expansions: ${!param}, ${param:offset[:len]}, ${param/pat[/str]},
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${!param*}
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compound array assignment
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negative subscripts for indexed array variables
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the `!' reserved word
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loadable builtins -- but ksh uses `builtin' while bash uses `enable'
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new $'...' and $"..." quoting
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@ -1174,6 +1245,7 @@ New things in ksh-93 present in bash-4.1:
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`command', `builtin', `disown' builtins
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echo -e
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exec -c/-a
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printf %T modifier
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read -A (bash uses read -a)
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read -t/-d
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trap -p
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@ -1193,6 +1265,7 @@ New things in ksh-93 present in bash-4.1:
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negative offsets in ${param:offset:length}
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redirection operators preceded with {varname} to store fd number in varname
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DEBUG can force skipping following command
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[[ -v var ]] operator (checks whether or not var is set)
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Section D: Why does bash do some things differently than other Unix shells?
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@ -1778,7 +1851,8 @@ compat40 set
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- the < and > operators to the [[ command do not consider the current
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locale when comparing strings
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- interrupting a command list such as "a ; b ; c" causes the execution
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of the entire list to be aborted
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of the entire list to be aborted (in versions before bash-4.0,
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interrupting one command in a list caused the next to be executed)
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Section F: Things to watch out for on certain Unix versions
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