Section C: Differences from other Unix shells C：跟其他UNIX shells脚本的区别 C1) How does bash differ from sh, the Bourne shell? C1） bash和 sh、Bourne shell的区别 This is a non-comprehensive list of features that differentiate bash from the SVR4.2 shell.  The bash manual page explains these more completely. 这时一个不全面的bash和SVR4.2 shell特性区别的列表，bash手册解释的更详细 Things bash has that sh does not: bash特有的功能：         long invocation options         长选项的调用         [+-]O invocation option         -l invocation option         `!' reserved word to invert pipeline return value          ！叹号保留字对管道返回的值取反         `time' reserved word to time pipelines and shell builtins          time保留字测试管道或内建命令耗时情况         the `function' reserved word         the `select' compound command and reserved word         select复合命令和保留字         arithmetic for command: for ((expr1 ; expr2; expr3 )); do list; done         算术命令：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)         $(<filename)形式的命令的替换，相当于$(cat filename)         the ${#param} parameter value length operator         ${#param} 测试参数param的值的长度         the ${!param} indirect parameter expansion operator         ${!param} 间接参数扩展操作         the ${!param*} prefix expansion operator         ${!param*} 前缀扩展操作         the ${param:offset[]} parameter substring operator        ${param:ffset[]}参数通过偏移量截取子串操作         the ${param/pat[/string]} parameter pattern substitution operator         ${param/pat[/string]} 参数模式替换的操作         expansions to perform substring removal (${p%[%]w}, ${p#[#]w})          扩展子串删除命令：(${p%[%]w}, ${p#[#]w})         expansion of positional parameters beyond $9 with ${num}         扩展了为止参数超过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         上边一堆的环境变量         DEBUG trap         ERR trap         调试和错误陷阱         variable arrays with new compound assignment syntax          数组和复合赋值运算符的语法规则         redirections: <>, &>, >|, <<<, [n]<&word-, [n]>&word-          重定向规则： <>, &>, >|, <<<, [n]<&word-, [n]>&word-         prompt string special char translation and variable expansion         提示字符串特殊字符的转化和变量展开         auto-export of variables in initial environment         自动继承初始化的环境变量         command search finds functions before builtins         命令搜查函数限于内建命令         bash return builtin will exit a file sourced with `.'         bash返回内建命令 将退出一个.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         上边一堆内建命令         bash reads ~/.bashrc for interactive shells, $ENV for non-interactive         bash reads这样写交互脚本，环境变量非交互的。         bash restricted shell mode is more extensive         bash更广泛的受限模式         bash allows functions and variables with the same name         允许函数名变量名一样         brace expansion         括号扩展         tilde expansion         ～波浪号扩展         arithmetic expansion with $((...)) and `let' builtin         算术扩展：$((...)) 和let命令         the `...' extended conditional command         `...` 命令扩展         process substitution         进程替换         aliases and alias/unalias builtins         别名的内建命令         local variables in functions and `local' builtin         函数内本地变量         readline and command-line editing with programmable completion         读取行和命令行可以编程完成         command history and history/fc builtins          查看历史命令         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          上边一堆新的bash内建命令。         exported functions         filename generation when using output redirection (command >a*)         重定向输出文件名的生成         POSIX.2-style globbing character classes         POSIX.2-style globbing equivalence classes         POSIX.2-style globbing collating symbols         POSIX.2风格的通配符类、等价类、通配符号         egrep-like extended pattern matching operators         case-insensitive pattern matching and globbing         不区分大小写的模式匹配和通配符         variable assignments preceding commands affect only that command,                 even for builtins and functions         变量赋值前的命令只影响那个命令，包括内建命令和函数         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         调试支持，包括caller内建命令和新变量         RETURN trap   Things sh has that bash does not: 下边是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: 执行情况的不同：         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 下边都和上边比较雷同了。。。大致浏览吧。 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