SHELL点滴

1.Shell判断文件是否存在

#!/bin/shmyPath="/var/log/httpd/"myFile="/var /log/httpd/access.log"# 这里的-x 参数判断$myPath是否存在并且是否具有可执行权限if [ ! -x "$myPath" ]; thenmkdir "$myPath"fi # 这里的-d 参数判断$myPath是否存在 if [ ! -d "$myPath" ]; then mkdir "$myPath" fi # 这里的-f参数判断$myFile是否存在 if [ ! -f "$myFile" ]; then touch "$myFile" fi # 其他参数还有-n,-n是判断一个变量是否是否有值 if [ ! -n "$myVar" ]; then echo "$myVar is empty" exit 0 fi # 两个变量判断是否相等 if [ "$var1" = "$var2" ]; then echo '$var1 eq $var2' else echo '$var1 not eq $var2' fi-f 和-e的区别 Conditional Logic on Files -a file exists. -b file exists and is a block special file. -c file exists and is a character special file. -d file exists and is a directory. -e file exists (just the same as -a). -f file exists and is a regular file. -g file exists and has its setgid(2) bit set. -G file exists and has the same group ID as this process. -k file exists and has its sticky bit set. -L file exists and is a symbolic link. -n string length is not zero. -o Named option is set on. -O file exists and is owned by the user ID of this process. -p file exists and is a first in, first out (FIFO) special file or named pipe. -r file exists and is readable by the current process. -s file exists and has a size greater than zero. -S file exists and is a socket. -t file descriptor number fildes is open and associated with a terminal device. -u file exists and has its setuid(2) bit set. -w file exists and is writable by the current process. -x file exists and is executable by the current process. -z string length is zero. 是用 -s 还是用 -f 这个区别是很大的！

2.Shell算术运算

$[1+2]  #value:3

`expr 1 + 2` #value:3

$((1 + 2)) #value:3

3.遍历文件的每行数据

while read lines

do

    echo $lines

done<filename#filename为文件名

4.提取行数据

awk语法：awk /pattern/{action} filename

awk简单用法

获取文件第一，列的数据:

awk '{print $1}' filename

5.显示日期格式为yyyyMMdd

date +%Y%m%d

6.Map通过key值排序的简单小例子(Java)

HashMap<String, String> map = new HashMap<String, String>();map.put("2012-07-04", "2012-07-04");map.put("2012-07-03", "2012-07-03");map.put("2012-07-07", "2012-07-07");map.put("2012-07-01", "2012-07-01");Object[] key = map.keySet().toArray();Arrays.sort(key);for (int i = 0; i < key.length; i++) {System.out.println(map.get(key[i]));}

7.">/dev/null 2>&1，以及2>1 VS 2>&1"的区别

a. 标准输入stdin文件描述符为0，标准输出stdout文件描述符为1，标准错误stderr文件描述符为2

b. /dev/null 空设备，相当于垃圾桶
c. 重定向符号：>
d. 2>1 与 2>&1 的区别
   2>1, 把标准错误stderr重定向到文件1中
   2>&1,把标准错误stderr重定向到标准输出stdout
e. 举例:
   假设有脚本test.sh，内容如下，t是一个不存在的命令，执行脚本进行下面测试。
   # cat test.sh
     t
     date


   标准输出重定向到log，错误信息输出到终端上，如下：
   # ./test.sh > log
     ./test.sh: line 1: t: command not found
   # cat log
     Thu Oct 23 22:53:02 CST 2008
   
   删除log文件，重新执行，这次是把标准输出定向到log，错误信息定向到文件1
   # ./test.sh > log 2>1
   #
   # cat log
   Thu Oct 23 22:56:20 CST 2008
   # cat 1
   ./test.sh: line 1: t: command not found
   #


   把标准输出重定向到log文件，把标准错误重定向到标准输出
   # ./test.sh > log 2>&1
   #
   # cat log
   ./test.sh: line 1: t: command not found
   Thu Oct 23 22:58:54 CST 2008
   #


   把错误信息重定向到空设备
   # ./test.sh 2>/dev/null
   Thu Oct 23 23:01:07 CST 2008