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@250-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@250-shiyan prog]# type -a fdisk for cd fdisk is /sbin/fdisk for is a shell keyword cd is a shell builtin [root@250-shiyan prog]# type -t fdisk for cd ls __udisks file keyword builtin
alias
function [root@250-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@250-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@250-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 0 or 1 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: 0 or 1 depending on value of EXPRESSION.
####.与source是一样的，就不再述。 [root@250-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@84-monitor ~]# cat a #!/bin/bash ip_conns=`ssh $1 "netstat -ant| grep EST | wc -l"` echo $ip_conns [root@84-monitor ~]# . a 192.168.2.109 862 [root@84-monitor ~]# . a 192.168.2.2 213 [root@84-monitor ~]# source a 192.168.2.225 22 [root@84-monitor ~]# source a 192.168.2.2 214
[root@250-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 0 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 0, let returns 1; let returns 0 otherwise.. [root@250-shiyan frag]# let num=5+8/2;echo $num 9 [root@250-shiyan frag]# let num=(5+8)/2;echo $num 6 [root@250-shiyan frag]# let num=5*2;echo $num 10 [root@250-shiyan frag]# let num=5/2;echo $num 2 [root@250-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 1 if EXPRESSION evaluates to 0; returns 0 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@250-shiyan frag]# ((num=5+2));echo $num 7 [root@250-shiyan frag]# let "num=5+2";echo $num 7 [root@250-shiyan frag]# x=`expr 5 \* 2`;echo $x 10 [root@250-shiyan frag]# echo "$(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 1 ，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 1 ，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@250-shiyan frag]# bash con1 the number is:1 the number is:2 the number is:3 the number is:8 the number is:9 the number is:10 [root@250-shiyan frag]# cat con1 for i in `seq 10` do if [ $i -gt 3 ] && [ $i -lt 8 ] then continue fi echo "the number is:$i" done [root@250-shiyan frag]# bash con1 the number is:1 the number is:2 the number is:4 the number is:5 the number is:6 the number is:7 the number is:9 the number is:10 [root@250-shiyan frag]# cat con1 for i in `seq 10` do if [ $i -eq 3 ] || [ $i -eq 8 ] then continue fi echo "the number is:$i" done break 退出本层循环 [root@250-shiyan frag]# bash con1 please input:q [root@250-shiyan frag]# bash con1 please input:Q [root@250-shiyan frag]# bash con1 please input: the number is:1 the number is:2 the number is:3 the number is:4 the number is:5 the number is:6 the number is:7 the number is:8 the number is:9 the number is:10 [root@250-shiyan frag]# cat con1 echo -n "please input:" read num for i in `seq 10` do if [ "$num" = "q" ] || [ "$num" = "Q" ] then break fi echo "the number is:$i" done [root@250-shiyan frag]# bash con1 please input:q [root@250-shiyan frag]# bash con1 please input:Q [root@250-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@250-shiyan ~]# history 984 2015-03-23 13:36:12 set +o history 985 2015-03-23 13:36:12 history 986 2015-03-23 13:36:12 echo $HISTSIZE 987 2015-03-23 13:36:12 env 988 2015-03-23 13:36:12 env|grep HIS 989 2015-03-23 13:36:12 vi .bash_history 990 2015-03-23 13:36:12 echo $HISTSIZE 991 2015-03-23 13:36:12 vi /etc/profile 992 2015-03-23 13:36:12 exit 993 2015-03-23 11:15:38 history 994 2015-03-23 11:16:54 free 995 2015-03-23 11:16:57 vmstat 1 996 2015-03-23 11:17:00 history 997 2015-03-23 11:17:39 exit 998 2015-03-23 11:54:12 history 999 2015-03-23 11:57:47 shopt -p 1000 2015-03-23 11:59:39 exit 1001 2015-03-23 13:36:15 history [root@250-shiyan ~]# cat .bash_history free #1427080617 vmstat 1 #1427080620 history #1427080659 exit #1427082852 history #1427083067 shopt -p #1427083179 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 1.41.12 (17-May-2010) Block size: 1024 再做设置，限制为204M，加入到启动文件中。 [root@localhost ~]# grep ulimit .bash_profile ulimit -f 204800 然后重新登录，再查看 [root@localhost ~]# ulimit -a|grep "file size" core file size (blocks, -c) 0 file size (blocks, -f) 204800 [root@localhost ~]# dd if=/dev/zero of=4.img File size limit exceeded [root@localhost ~]# ll total 819256 -rw-r--r--. 1 root root 16 May 17 2015 123 -rw-r--r--. 1 root root 209715200 Feb 8 21:34 1.img -rw-r--r--. 1 root root 209715200 Feb 8 21:38 2.img -rw-r--r--. 1 root root 209715200 Feb 8 21:40 3.img -rw-r--r--. 1 root root 209715200 Feb 8 21:46 4.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
