sh,bash,csh,tcsh等shell的区别

痛定思痛。 2022-05-26 08:19 251阅读 0赞

转自 [http:///blog.sina.com.cn/s/blog\_655edca101010sd4.html][http_blog.sina.com.cn_s_blog_655edca101010sd4.html]

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**1.Introduction**  
  
Bourne Shell(即sh)是UNIX最初使用的shell，平且在每种UNIX上都可以使用。Bourne Shell在shell编程方便相当优秀，但在处理与用户的交互方便作得不如其他几种shell。  
  
LinuxOS默认的是Bourne Again Shell，它是Bourne Shell的扩展，简称bash，与Bourne Shell完全兼容，并且在Bourne Shell的基础上增加，增强了很多特性。可以提供命令补全，命令编辑和命令历史等功能。它还包含了很多C Shell和Korn Shell中的优点，有灵活和强大的编辑接口，同时又很友好的用户界面  
  
C Shell是一种比Bourne Shell更适合的变种Shell，它的语法与C语言很相似。Linux为喜欢使用C Shell的人提供了Tcsh。  
  
Tcsh是C Shell的一个扩展版本。Tcsh包括命令行编辑，可编程单词补全，拼写校正，历史命令替换，作业控制和类似C语言的语法，他不仅和Bash Shell提示符兼容，而且还提供比Bash Shell更多的提示符参数。  
  
Korn Shell集合了C Shell和Bourne Shell的优点并且和Bourne Shell完全兼容。Linux系统提供了pdksh（ksh的扩展），它支持人物控制，可以在命令行上挂起，后台执行，唤醒或终止程序。  
  
Linux还包括了一些流行的Shell 如：ash，zsh等。每个Shell都有它的用途，有些Shell是有专利的，有些能从Internet或其他来源获得。

**2.How does bash differ from sh, the Bourne shell?**  
  
This is a non-comprehensive list of features that differentiate bash from the SVR4.2 shell.  The bash manual page explains these more completely.  
  
Things bash has that sh does not:  
        long invocation options  
        \[+-\]O invocation option  
        -l invocation option  
        \`!' reserved word to invert pipeline return value  
        \`time' reserved word to time pipelines and shell builtins  
        the \`function' reserved word  
        the \`select' compound command and reserved word  
        arithmetic for command: for ((expr1 ; expr2; expr3 )); do list; done  
        new $'...' and $"..." quoting  
        the $(...) form of command substitution  
        the $(<filename) form of command substitution, equivalent to  
                $(cat filename)  
        the $\{\#param\} parameter value length operator  
        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  
        expansions to perform substring removal ($\{p%\[%\]w\}, $\{p\#\[\#\]w\})  
        expansion of positional parameters beyond $9 with $\{num\}  
        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  
        DEBUG trap  
        ERR trap  
        variable arrays with new compound assignment syntax  
        redirections: <>, &>, >|, <<<, \[n\]<&word-, \[n\]>&word-  
        prompt string special char translation and variable expansion  
        auto-export of variables in initial environment  
        command search finds functions before builtins  
        bash return builtin will exit a file sourced with \`.'  
        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  
        bash reads ~/.bashrc for interactive shells, $ENV for non-interactive  
        bash restricted shell mode is more extensive  
        bash allows functions and variables with the same name  
        brace expansion  
        tilde expansion  
        arithmetic expansion with $((...)) and \`let' builtin  
        the \`...' extended conditional command  
        process substitution  
        aliases and alias/unalias builtins  
        local variables in functions and \`local' builtin  
        readline and command-line editing with programmable completion  
        command history and history/fc builtins  
        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  
        exported functions  
        filename generation when using output redirection (command >a\*)  
        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  
        variable assignments preceding commands affect only that command,even for builtins and functions  
        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  
        RETURN trap  
  
Things sh has that bash does not:  
        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:  
        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

**3.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  
  
  
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

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