bash内部命令-2

http://www.gnu.org/software/bash/

http://www.tldp.org/HOWTO/Bash-Prompt-HOWTO/

[root@250-shiyan ~]# rpm -qa|grep bash
bash-4.1.2-15.el6_4.x86_64
type-.-source-let-(())-history-declare

[root@-shiyan prog]# help type
type: type [-afptP] name [name ...]
    Display information about command type.

    For each NAME, indicate how it would be interpreted if used as a
    command name.

    Options:
      -a        display all locations containing an executable named NAME;
        includes aliases, builtins, and functions, if and only if
        the `-p' option is not also used
      -f        suppress shell function lookup
      -P        force a PATH search for each NAME, even if it is an alias,
        builtin, or function, and returns the name of the disk file
        that would be executed
      -p        returns either the name of the disk file that would be executed,
        or nothing if `type -t NAME' would not return `file'.
####要么返回可能被执行的磁盘文件名，要么假如type -t NAME不返回file则什么也不做。
      -t        output a single word which is one of `alias', `keyword',
        `function', `builtin', `file' or `', if NAME is an alias, shell
        reserved word, shell function, shell builtin, disk file, or not
        found, respectively
####如果NAME是一个别名，shell保留字，shell函数，shell内部命令，磁盘file，或者没找到，那么分别对应输出alias,keyword,function,builtin,file,或者空的其中一个单词。
    Arguments:
      NAME      Command name to be interpreted.
####被解读的命令名
    Exit Status:
    Returns success if all of the NAMEs are found; fails if any are not found.
####假如所有的NAMEs都找到返回成功;假如任何一个未找到就返回失败。
typeset: typeset [-aAfFilrtux] [-p] name[=value] ...
    Set variable values and attributes.

    Obsolete.  See `help declare'.

[root@-shiyan prog]# type -a fdisk for cd
fdisk is /sbin/fdisk
for is a shell keyword
cd is a shell builtin
[root@-shiyan prog]# type -t fdisk for cd ls __udisks
file
keyword
builtin
alias
function
[root@-shiyan prog]# type -p dir fdisk
/usr/bin/dir
/sbin/fdisk
[root@250-shiyan prog]# declare -f|more　　先查看函数名，再查看类型
[root@250-shiyan prog]# type __udisks
__udisks is a function

[root@250-shiyan frag]# type -a : [[ {
: is a shell builtin
[[ is a shell keyword
{ is a shell keyword
[root@250-shiyan frag]# type -a [
[ is a shell builtin
[ is /usr/bin/[

[root@-shiyan frag]# help :
:: :
    Null command.

    No effect; the command does nothing.

    Exit Status:
    Always succeeds.

http://blog.csdn.net/ysdaniel/article/details/7905818    Shell中[和[[的异同
[root@-shiyan frag]# help [
[: [ arg... ]
    Evaluate conditional expression.

    This is a synonym for the "test" builtin, but the last argument must
    be a literal `]', to match the opening `['.
####是内置test的同义词，但最后一个参数必须是一个字符],来匹配开始的[
[[ ... ]]: [[ expression ]]
    Execute conditional command.

    Returns a status of  or  depending on the evaluation of the conditional
    expression EXPRESSION.  Expressions are composed of the same primaries used
    by the `test' builtin, and may be combined using the following operators:

      ( EXPRESSION )    Returns the value of EXPRESSION
      ! EXPRESSION              True if EXPRESSION is false; else false
      EXPR1 && EXPR2    True if both EXPR1 and EXPR2 are true; else false
      EXPR1 || EXPR2    True if either EXPR1 or EXPR2 is true; else false

    When the `==' and `!=' operators are used, the string to the right of
    the operator is used as a pattern and pattern matching is performed.
    When the `=~' operator is used, the string to the right of the operator
    is matched as a regular expression.

    The && and || operators do not evaluate EXPR2 if EXPR1 is sufficient to
    determine the expression's value.

    Exit Status:
     or  depending on value of EXPRESSION.

####.与source是一样的，就不再述。
[root@-shiyan frag]# help .
.: . filename [arguments]
    Execute commands from a file in the current shell.
####在当前shell中，从一个文件中执行命令。
    Read and execute commands from FILENAME in the current shell.  The
    entries in $PATH are used to find the directory containing FILENAME.
    If any ARGUMENTS are supplied, they become the positional parameters
    when FILENAME is executed.
####在当前shell中，从FILENAME中读取并执行命令。在$PATH中的项目是被用作查找包括FILENAME的目录。当FILENAME被执行时，如果有参数供应，他们将成为位置参数。
    Exit Status:
    Returns the status of the last command executed in FILENAME; fails if
    FILENAME cannot be read.

[root@-monitor ~]# cat a
#!/bin/bash
ip_conns=`ssh $ "netstat -ant| grep EST | wc -l"`
echo $ip_conns
[root@-monitor ~]# . a 192.168.2.109

[root@-monitor ~]# . a 192.168.2.2

[root@-monitor ~]# source a 192.168.2.225

[root@-monitor ~]# source a 192.168.2.2

[root@-shiyan frag]# help let
let: let arg [arg ...]
    Evaluate arithmetic expressions.

    Evaluate each ARG as an arithmetic expression.  Evaluation is done in
    fixed-width integers with no check for overflow, though division by
    is trapped and flagged as an error.  The following list of operators is
    grouped into levels of equal-precedence operators.  The levels are listed
    in order of decreasing precedence.
####按照优先级的降序列出
        id++, id--      variable post-increment, post-decrement
        ++id, --id      variable pre-increment, pre-decrement
        -, +            unary minus, plus
        !, ~            logical and bitwise negation
        **              exponentiation
        *, /, %         multiplication, division, remainder
        +, -            addition, subtraction
        <<, >>          left and right bitwise shifts
        <=, >=, <, >    comparison
        ==, !=          equality, inequality
        &               bitwise AND
        ^               bitwise XOR
        |               bitwise OR
        &&              logical AND
        ||              logical OR
        expr ? expr : expr
                        conditional operator
        =, *=, /=, %=,
        +=, -=, <<=, >>=,
        &=, ^=, |=      assignment

    Shell variables are allowed as operands.  The name of the variable
    is replaced by its value (coerced to a fixed-width integer) within
    an expression.  The variable need not have its integer attribute
    turned on to be used in an expression.

####shell变量被允许作为操作数。在一个表达式里，变量的名字被替换为它的值。

    Operators are evaluated in order of precedence.  Sub-expressions in
    parentheses are evaluated first and may override the precedence
    rules above.
####操作符按照优先顺序被求值，在小括号里的子表达式首先被求值，并且可以覆盖上文的优先规则。

    Exit Status:
    If the last ARG evaluates to , let returns ; let returns  otherwise..

[root@-shiyan frag]# let num=+/;echo $num

[root@-shiyan frag]# let num=(+)/;echo $num

[root@-shiyan frag]# let num=*;echo $num

[root@-shiyan frag]# let num=/;echo $num

[root@-shiyan frag]# help \(
(( ... )): (( expression ))
    Evaluate arithmetic expression.

    The EXPRESSION is evaluated according to the rules for arithmetic
    evaluation.  Equivalent to "let EXPRESSION".

    Exit Status:
    Returns  if EXPRESSION evaluates to ; returns  otherwise.

shell里的4种运算格式，只有bc与awk可以浮点运算，其它三个只能整数运算。
[root@-shiyan frag]# ((num=+));echo $num

[root@-shiyan frag]# let "num=5+2";echo $num

[root@-shiyan frag]# x=`expr  \* `;echo $x

[root@-shiyan frag]# echo "$(echo 'scale=2;40*100/90' | bc)%"
44.44%

while loop 的原理与 for loop 稍有不同：它不是逐次处理清单中的变量值，而是取决于 while 后面的命令行之 return value ：
* 若为 ture ，则执行 do 与 done 之间的命令，然后重新判断 while 后的 return value 。
* 若为 false ，则不再执行 do 与 done 之间的命令而结束循环。
* 若 while 的测试结果永远为 true 的话，那循环将一直永久执行下去：
一旦你能够理解 while loop 的话，那就能理解 until loop ：
* 与 while 相反，until 是在 return value 为 false 时进入循环，否则结束。
在结束本shell之前，再跟大家补充两个与 loop 有关的命令：
* break
* continue
这两个命令常用在复合式循环里，也就是在do ... done之间又有更进一层的 loop,当然，用在单一循环中也未尝不可啦... ^_^
break 是用来打断循环，也就是"强迫结束" 循环。若 break 后面指定一个数值 n 的话，则"从里向外"打断第 n 个循环，默认值为 break  ，也就是打断当前的循环。
在使用 break 时需要注意的是，它与 return 及 exit 是不同的：
* break 是结束 loop
* return 是结束 function
* exit 是结束 script/shell
而 continue 则与 break 相反：强迫进入下一次循环动作。若你理解不来的话，那你可简单的看成：在 continue 到 done 之间的句子略过而返回循环顶端...与 break 相同的是：continue 后面也可指定一个数值 n ，以决定继续哪一层(从里向外计算)的循环，默认值为 continue  ，也就是继续当前的循环。

continue
恢复下一次迭代循环，本次就不执行了
下面这个脚本说明，如果文件名中有while,则不输出，如果想要只输出while行，只需要将=改为!=即可。这就是continue的作用。
#!/bin/bash
for shname in `ls *.sh`
do
  name=`echo "$shname" | awk -F. '{print $1}'`
  if [ $name = while ]
  then
  continue
  fi
  echo $name
done
符合条件的，结束本次循环
[root@-shiyan frag]# bash con1
the number is:
the number is:
the number is:
the number is:
the number is:
the number is:
[root@-shiyan frag]# cat con1
for i in `seq `
   do
    if [ $i -gt  ] && [ $i -lt  ]
    then
       continue
    fi
    echo "the number is:$i"
   done
[root@-shiyan frag]# bash con1
the number is:
the number is:
the number is:
the number is:
the number is:
the number is:
the number is:
the number is:
[root@-shiyan frag]# cat con1
for i in `seq `
   do
    if [ $i -eq  ] || [ $i -eq  ]
    then
       continue
    fi
    echo "the number is:$i"
   done

break
退出本层循环
[root@-shiyan frag]# bash con1
please input:q
[root@-shiyan frag]# bash con1
please input:Q
[root@-shiyan frag]# bash con1
please input:
the number is:
the number is:
the number is:
the number is:
the number is:
the number is:
the number is:
the number is:
the number is:
the number is:
[root@-shiyan frag]# cat con1
echo -n "please input:"
read num
for i in `seq `
   do
    if [ "$num" = "q" ] || [ "$num" = "Q" ]
    then
       break
    fi
    echo "the number is:$i"
   done
[root@-shiyan frag]# bash con1
please input:q
[root@-shiyan frag]# bash con1
please input:Q
[root@-shiyan frag]#

http://www.dedecms.com/knowledge/servers/linux-bsd/2012/0706/2700_2.html

echo "export HISTTIMEFORMAT='%F %T '" >> /etc/profile

当你从命令行执行 history 命令后，通常只会显示已执行命令的序号和命令本身。如果你想要查看命令历史的时间戳，那么可以执行：
# export HISTTIMEFORMAT='%F %T '
[root@-shiyan ~]# history
    -- :: set +o history
    -- :: history
    -- :: echo $HISTSIZE
    -- :: env
    -- :: env|grep HIS
    -- :: vi .bash_history
    -- :: echo $HISTSIZE
    -- :: vi /etc/profile
    -- :: exit
    -- :: history
    -- :: free
    -- :: vmstat
    -- :: history
    -- :: exit
    -- :: history
    -- :: shopt -p
   -- :: exit
   -- :: history
[root@-shiyan ~]# cat .bash_history
free
#
vmstat
#
history
#
exit
#
history
#
shopt -p
#
exit

[root@250-shiyan ~]# echo !yum:1
echo install
install
注意：这个功能只能用在当 HISTTIMEFORMAT 这个环境变量被设置之后，之后的那些新执行的 bash 命令才会被打上正确的时间戳。在此之前的所有命令，都将会显示成设置 HISTTIMEFORMAT 变量的时间。

shell变量仅供shell builtins,function,keyword,来使用。
环境变量供shell以外的程序来使用。
shell变量
HISTFILE
HISTSIZE
HISTFILESIZE
HISTTIMEFORMAT
HISTCONTROL
HISTIGNORE

shell选项
cmdhist
lithist
histappend

declare或typeset内建命令(它们是完全相同的)可以用来限定变量的属性.这是在某些编程语言中使用的定义类型不严格的方式。命令declare是bash版本2之后才有的。命令typeset也可以在ksh脚本中运行。
功能说明：声明 shell 变量。
语　　法：declare [+/-][rxi][变量名称＝设置值] 或 declare -f
补充说明：declare为shell指令，在第一种语法中可用来声明变量并设置变量的属性([rix]即为变量的属性），在第二种语法中可用来显示shell函数。若不加上任何参数，则会显示全部的shell变量与函数(与执行set指令的效果相同)。
参　　数：
　+/- 　"-"可用来指定变量的属性，"+"则是取消变量所设的属性。
　-f 　仅显示函数。
　r 　将变量设置为只读。
　x 　指定的变量会成为环境变量，可供shell以外的程序来使用。
　i 　[设置值]可以是数值，字符串或运算式。
declare/typeset 选项
-r 只读
declare -r var1
    (declare -r var1与readonly var1作用相同)
    这大致和C的const限定词相同.一个试图改变只读变量值的操作将会引起错误信息而失败.

[root@localhost ~]# rpm -qf /etc/security/
pam-1.1.1-13.el6.x86_64
下面的几个文件是由pam生成的，它也会影响到资源限制。
/etc/security/limits.conf
/etc/security/limits.d
/etc/security/limits.d/90-nproc.conf

先查看块大小，得到单位为K。
[root@localhost ~]# dumpe2fs  /dev/sda1 |grep "Block size"
dumpe2fs 1.41. (-May-)
Block size:
再做设置，限制为204M，加入到启动文件中。
[root@localhost ~]# grep ulimit .bash_profile
ulimit -f
然后重新登录，再查看
[root@localhost ~]# ulimit -a|grep "file size"
core file size          (blocks, -c)
file size               (blocks, -f)
[root@localhost ~]# dd if=/dev/zero of=.img
File size limit exceeded
[root@localhost ~]# ll
total
-rw-r--r--.  root root         May
-rw-r--r--.  root root  Feb   : .img
-rw-r--r--.  root root  Feb   : .img
-rw-r--r--.  root root  Feb   : .img
-rw-r--r--.  root root  Feb   : .img
由此可知，ulimit -f不限制由此终端的shell的总文件大小，而是单次上限。

pending signals　　未处理信号，等待信号。

删除除某个目录之外的所有
只需要开启下面这个模式匹配功能，就可以用除*,?之外的通配符了
shopt -s extglob
rm -rf !(bbs)
rm -rf !(bbs|cc)
删除当前目录下除bbs目录外所有的文件，真方便
也可以用下面的这条命令
ls |grep -v bbs |xargs rm -f

[root@cs-manage sh]# ffile=/dir1/dir2/dir3/my.file.txt
[root@cs-manage sh]# echo ${ffile/dir/}
/1/dir2/dir3/my.file.txt
[root@cs-manage sh]# echo ${ffile//dir/}
/1/2/3/my.file.txt
[root@cs-manage sh]# echo ${ffile/#/oi}
oi/dir1/dir2/dir3/my.file.txt
[root@cs-manage sh]# echo ${ffile/%/oi}
/dir1/dir2/dir3/my.file.txtoi
[root@cs-manage sh]# echo ${ffile/%t/oi}
/dir1/dir2/dir3/my.file.txoi

Bash的=~正则表达式匹配
http://zengrong.net/post/1563.htm

简洁的bash编程技巧
http://www.open-open.com/lib/view/open1352264103719.html