Section C: Differences from other Unix shells
C：跟其他UNIX shells腳本的區別
C1) How does bash differ from sh, the Bourne shell?
C1） bash和 sh、Bourne shell的區別
This is a non-comprehensive list of features that differentiate bash
from the SVR4.2 shell.  The bash manual page explains these more
completely.
這時一個不全面的bash和SVR4.2 shell特性區別的列表，bash手冊解釋的更詳細
Things bash has that sh does not:
bash特有的功能：
        long invocation options
        長選項的調用
        [+-]O invocation option
        -l invocation option
        `!' reserved word to invert pipeline return value
         ！嘆號保留字對管道返回的值取反
        `time' reserved word to time pipelines and shell builtins
         time保留字測試管道或內建命令耗時情況
        the `function' reserved word
        the `select' compound command and reserved word
        select復合命令和保留字
        arithmetic for command: for ((expr1 ; expr2; expr3 )); do list; done
        算術命令：for ((expr1 ; expr2; expr3 )); do list; done
        new $'...' and $"..." quoting
        新的引用方法$'...'  $"..."
        the $(...) form of command substitution
        $(...) 命令替代用法
        the $(filename) form of command substitution, equivalent to
                $(cat filename)
        $(filename)形式的命令的替換，相當于$(cat filename)
        the ${#param} parameter value length operator
        ${#param} 測試參數param的值的長度
        the ${!param} indirect parameter expansion operator
        ${!param} 間接參數擴展操作
        the ${!param*} prefix expansion operator
        ${!param*} 前綴擴展操作
        the ${param:offset[]} parameter substring operator
       ${param:ffset[]}參數通過偏移量截取子串操作
        the ${param/pat[/string]} parameter pattern substitution operator
        ${param/pat[/string]} 參數模式替換的操作
        expansions to perform substring removal (${p%[%]w}, ${p#[#]w})
         擴展子串刪除命令：(${p%[%]w}, ${p#[#]w})
        expansion of positional parameters beyond $9 with ${num}
        擴展了為止參數超過9的限制
        variables: BASH, BASH_VERSION, BASH_VERSINFO, UID, EUID, REPLY,
                   TIMEFORMAT, PPID, PWD, OLDPWD, SHLVL, RANDOM, SECONDS,
                   LINENO, HISTCMD, HOSTTYPE, OSTYPE, MACHTYPE, HOSTNAME,
                   ENV, PS3, PS4, DIRSTACK, PIPESTATUS, HISTSIZE, HISTFILE,
                   HISTFILESIZE, HISTCONTROL, HISTIGNORE, GLOBIGNORE, GROUPS,
                   PROMPT_COMMAND, FCEDIT, FIGNORE, IGNOREEOF, INPUTRC,
                   SHELLOPTS, OPTERR, HOSTFILE, TMOUT, FUNCNAME, histchars,
                   auto_resume
        上邊一堆的環境變量
        DEBUG trap
        ERR trap
        調試和錯誤陷阱
        variable arrays with new compound assignment syntax
         數組和復合賦值運算符的語法規則
        redirections: >, >, >|, , [n]word-, [n]>word-
         重定向規則： >, >, >|, , [n]word-, [n]>word-
        prompt string special char translation and variable expansion
        提示字符串特殊字符的轉化和變量展開
        auto-export of variables in initial environment
        自動繼承初始化的環境變量
        command search finds functions before builtins
        命令搜查函數限于內建命令
        bash return builtin will exit a file sourced with `.'
        bash返回內建命令 將退出一個.文件源
        builtins: cd -/-L/-P, exec -l/-c/-a, echo -e/-E, hash -d/-l/-p/-t.
                  export -n/-f/-p/name=value, pwd -L/-P,
                  read -e/-p/-a/-t/-n/-d/-s/-u,
                  readonly -a/-f/name=value, trap -l, set +o,
                  set -b/-m/-o option/-h/-p/-B/-C/-H/-P,
                  unset -f/-v, ulimit -m/-p/-u,
                  type -a/-p/-t/-f/-P, suspend -f, kill -n,
                  test -o optname/s1 == s2/s1 s2/s1 > s2/-nt/-ot/-ef/-O/-G/-S
        上邊一堆內建命令
        bash reads ~/.bashrc for interactive shells, $ENV for non-interactive
        bash reads這樣寫交互腳本，環境變量非交互的。
        bash restricted shell mode is more extensive
        bash更廣泛的受限模式
        bash allows functions and variables with the same name
        允許函數名變量名一樣
        brace expansion
        括號擴展
        tilde expansion
        ～波浪號擴展
        arithmetic expansion with $((...)) and `let' builtin
        算術擴展：$((...)) 和let命令
        the `...' extended conditional command
        `...` 命令擴展
        process substitution
        進程替換
        aliases and alias/unalias builtins
        別名的內建命令
        local variables in functions and `local' builtin
        函數內本地變量
        readline and command-line editing with programmable completion
        讀取行和命令行可以編程完成
        command history and history/fc builtins
         查看歷史命令
        csh-like history expansion
        other new bash builtins: bind, command, compgen, complete, builtin,
                                 declare/typeset, dirs, enable, fc, help,
                                 history, logout, popd, pushd, disown, shopt,
                                 printf
         上邊一堆新的bash內建命令。
        exported functions
        filename generation when using output redirection (command >a*)
        重定向輸出文件名的生成
        POSIX.2-style globbing character classes
        POSIX.2-style globbing equivalence classes
        POSIX.2-style globbing collating symbols
        POSIX.2風格的通配符類、等價類、通配符號
        egrep-like extended pattern matching operators
        case-insensitive pattern matching and globbing
        不區分大小寫的模式匹配和通配符
        variable assignments preceding commands affect only that command,
                even for builtins and functions
        變量賦值前的命令只影響那個命令，包括內建命令和函數
        posix mode
        redirection to /dev/fd/N, /dev/stdin, /dev/stdout, /dev/stderr,
                /dev/tcp/host/port, /dev/udp/host/port
        debugger support, including `caller' builtin and new variables
        調試支持，包括caller內建命令和新變量
        RETURN trap

 
Things sh has that bash does not:
下邊是sh有但是bash木有的
        uses variable SHACCT to do shell accounting
        includes `stop' builtin (bash can use alias stop='kill -s STOP')
        `newgrp' builtin
        turns on job control if called as `jsh'
        $TIMEOUT (like bash $TMOUT)
        `^' is a synonym for `|'
        new SVR4.2 sh builtins: mldmode, priv

Implementation differences:
執行情況的不同：
        redirection to/from compound commands causes sh to create a subshell
        bash does not allow unbalanced quotes; sh silently inserts them at EOF
        bash does not mess with signal 11
        sh sets (euid, egid) to (uid, gid) if -p not supplied and uid 100
        bash splits only the results of expansions on IFS, using POSIX.2
                field splitting rules; sh splits all words on IFS
        sh does not allow MAILCHECK to be unset (?)
        sh does not allow traps on SIGALRM or SIGCHLD
        bash allows multiple option arguments when invoked (e.g. -x -v);
                sh allows only a single option argument (`sh -x -v' attempts
                to open a file named `-v', and, on SunOS 4.1.4, dumps core.
                On Solaris 2.4 and earlier versions, sh goes into an infinite
                loop.)
        sh exits a script if any builtin fails; bash exits only if one of
                the POSIX.2 `special' builtins fails

下邊都和上邊比較雷同了。。。大致瀏覽吧。
C2) How does bash differ from the Korn shell, version ksh88?

Things bash has or uses that ksh88 does not:
        long invocation options
        [-+]O invocation option
        -l invocation option
        `!' reserved word
        arithmetic for command: for ((expr1 ; expr2; expr3 )); do list; done
        arithmetic in largest machine-supported size (intmax_t)
        posix mode and posix conformance
        command hashing
        tilde expansion for assignment statements that look like $PATH
        process substitution with named pipes if /dev/fd is not available
        the ${!param} indirect parameter expansion operator
        the ${!param*} prefix expansion operator
        the ${param:offset[]} parameter substring operator
        the ${param/pat[/string]} parameter pattern substitution operator
        variables: BASH, BASH_VERSION, BASH_VERSINFO, UID, EUID, SHLVL,
                   TIMEFORMAT, HISTCMD, HOSTTYPE, OSTYPE, MACHTYPE,
                   HISTFILESIZE, HISTIGNORE, HISTCONTROL, PROMPT_COMMAND,
                   IGNOREEOF, FIGNORE, INPUTRC, HOSTFILE, DIRSTACK,
                   PIPESTATUS, HOSTNAME, OPTERR, SHELLOPTS, GLOBIGNORE,
                   GROUPS, FUNCNAME, histchars, auto_resume
        prompt expansion with backslash escapes and command substitution
        redirection: > (stdout and stderr), , [n]word-, [n]>word-
        more extensive and extensible editing and programmable completion
        builtins: bind, builtin, command, declare, dirs, echo -e/-E, enable,
                  exec -l/-c/-a, fc -s, export -n/-f/-p, hash, help, history,
                  jobs -x/-r/-s, kill -s/-n/-l, local, logout, popd, pushd,
                  read -e/-p/-a/-t/-n/-d/-s, readonly -a/-n/-f/-p,
                  set -o braceexpand/-o histexpand/-o interactive-comments/
                  -o notify/-o physical/-o posix/-o hashall/-o onecmd/
                  -h/-B/-C/-b/-H/-P, set +o, suspend, trap -l, type,
                  typeset -a/-F/-p, ulimit -u, umask -S, alias -p, shopt,
                  disown, printf, complete, compgen
        `!' csh-style history expansion
        POSIX.2-style globbing character classes
        POSIX.2-style globbing equivalence classes
        POSIX.2-style globbing collating symbols
        egrep-like extended pattern matching operators
        case-insensitive pattern matching and globbing
        `**' arithmetic operator to do exponentiation
        redirection to /dev/fd/N, /dev/stdin, /dev/stdout, /dev/stderr
        arrays of unlimited size
        TMOUT is default timeout for `read' and `select'
        debugger support, including the `caller' builtin
        RETURN trap
        Timestamps in history entries
        {x..y} brace expansion

Things ksh88 has or uses that bash does not:
        tracked aliases (alias -t)
        variables: ERRNO, FPATH, EDITOR, VISUAL
        co-processes (|, >p, p)
        weirdly-scoped functions
        typeset +f to list all function names without definitions
        text of command history kept in a file, not memory
        builtins: alias -x, cd old new, newgrp, print,
                  read -p/-s/var?prompt, set -A/-o gmacs/
                  -o bgnice/-o markdirs/-o trackall/-o viraw/-s,
                  typeset -H/-L/-R/-Z/-A/-ft/-fu/-fx/-l/-u/-t, whence
        using environment to pass attributes of exported variables
        arithmetic evaluation done on arguments to some builtins
        reads .profile from $PWD when invoked as login shell

Implementation differences:
        ksh runs last command of a pipeline in parent shell context
        bash has brace expansion by default (ksh88 compile-time option)
        bash has fixed startup file for all interactive shells; ksh reads $ENV
        bash has exported functions
        bash command search finds functions before builtins
        bash waits for all commands in pipeline to exit before returning status
        emacs-mode editing has some slightly different key bindings

 
C3) Which new features in ksh-93 are not in bash, and which are?

New things in ksh-93 not in bash-3.0:
        associative arrays
        floating point arithmetic and variables
        math library functions
        ${!name[sub]} name of subscript for associative array
        `.' is allowed in variable names to create a hierarchical namespace
        more extensive compound assignment syntax
        discipline functions
        `sleep' and `getconf' builtins (bash has loadable versions)
        typeset -n and `nameref' variables
        KEYBD trap
        variables: .sh.edchar, .sh.edmode, .sh.edcol, .sh.edtext, .sh.version,
                   .sh.name, .sh.subscript, .sh.value, .sh.match, HISTEDIT
        backreferences in pattern matching (\N)
        `' operator in pattern lists for matching
        print -f (bash uses printf)
        `fc' has been renamed to `hist'
        `.' can execute shell functions
        exit statuses between 0 and 255
        `+=' variable assignment operator
        FPATH and PATH mixing
        getopts -a
        -I invocation option
        printf %H, %P, %T, %Z modifiers, output base for %d
        lexical scoping for local variables in `ksh' functions
        no scoping for local variables in `POSIX' functions

New things in ksh-93 present in bash-3.0:
        [n]word- and [n]>word- redirections (combination dup and close)
        for (( expr1; expr2; expr3 )) ; do list; done - arithmetic for command
        ?:, ++, --, `expr1 , expr2' arithmetic operators
        expansions: ${!param}, ${param:offset[]}, ${param/pat[/str]},
                    ${!param*}
        compound array assignment
        the `!' reserved word
        loadable builtins -- but ksh uses `builtin' while bash uses `enable'
        `command', `builtin', `disown' builtins
        new $'...' and $"..." quoting
        FIGNORE (but bash uses GLOBIGNORE), HISTCMD
        set -o notify/-C
        changes to kill builtin
        read -A (bash uses read -a)
        read -t/-d
        trap -p
        exec -c/-a
        `.' restores the positional parameters when it completes
        POSIX.2 `test'
        umask -S
        unalias -a
        command and arithmetic substitution performed on PS1, PS4, and ENV
        command name completion
        ENV processed only for interactive shells
        set -o pipefail