WindowsBatch与LinuxShell比较[变量值来源于文件或命令]

一 Windows Batch

1) 如果变量的值来自文件，则必须类似set /p num=<num.txt 。
2）如果变量的值想来自命令的结果，则一些命令可以使用%%，例如set bbb=%time%，set aaa=%date%。对于一般的命令只能先输出到临时文件，然后再读入，例如time /t > ddd.txt set /p ddd=<ddd.txt。
3) 在for中可以使用命令，例如·time /t·。

实例：

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />-->@echooff

echo get the value from one txt file
rem the num.txt file only contains one line "001".

echo work well
set/p num=<num.txt
echo %num%

echo doesn't work
set num=<num.txt
echo %num%
type num.txt | set num=
echo %num%
type num.txt | set/p num=
echo %num%
set num=(`print num.txt`)
echo %num%

echo get value from command
echo some command work well, such as %time%, %date%
set bbb=%time%
echo %bbb%
set aaa=%date%
echo %aaa%

echo general command doesn't work
set ccc=('time/t')
echo %ccc%

echo one solution is to output the result to txt and then input it
time/t > ddd.txt
set/p ddd=<ddd.txt
echo %ddd%

echo specially,in for clause,('time/t') is as one command.
echo and if also usesetlocal enabledelayedexpansion, the way also can implement get value from command.
setlocal enabledelayedexpansion
for/f %%i in ('time/t')do(
echo %%i
set ti=%%i
echo !ti!
)

pause

二 Linux Shell

1）超级简单，只需要使用·command parameters·。

实例：

<!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />-->#!/bin/sh

ddd=`cat ./ddd.txt`
echo$ddd

d=`date`
echo$d

完！