shell:for和while用法

寫法一：
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#!/bin/bash

while read line
do
    echo $line
done < file(待讀取的文件)
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寫法二：（併發腳本慎用，grep不能輸出全部匹配的信息）
----------------------------------------------------------------------------
#!/bin/bash

cat file(待讀取的文件) | while read line
do
    echo $line
done
----------------------------------------------------------------------------

寫法三：
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for line in `cat file(待讀取的文件)`
do
    echo $line
done
----------------------------------------------------------------------------

說明：
for逐行讀和while逐行讀是有區別的,如:
$ cat file
aaaa
bbbb  fff  ggg
cccc dddd

$ cat file | while read line; do echo $line; done
aaaa
bbbb  fff  ggg
cccc dddd

$ for line in $(<file); do echo $line; done
 

aaaa
bbbb
fff
ggg
cccc
dddd