出自bash的faq，仔细看看。顺便翻译学习一下。
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