sed命令的"指定开头"和全局匹配

feedforward

1. zouboan@hp:~/G/NuttX/apps/examples/elf/tests/errno$ cat xx.txt  ##xx.txt的内容
   
2. hello hello hello  
   
3.    hello  hello
   
4. hello  hello hello

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1. zouboan@hp:~/G/NuttX/apps/examples/elf/tests/errno$ sed 's/hello/nihao/' xx.txt
   
2. nihao hello hello  
   
3.    nihao  hello
   
4. nihao  hello hello
   
5. ##不指定开头，也不加g，结果是匹配到一个符合的字段就直接跳到下一行

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1. zouboan@hp:~/G/NuttX/apps/examples/elf/tests/errno$ sed 's/hello/nihao/g' xx.txt ##不指定开头，加g，匹配全部
   
2. nihao nihao nihao  
   
3.    nihao  nihao
   
4. nihao  nihao nihao

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1. zouboan@hp:~/G/NuttX/apps/examples/elf/tests/errno$sed 's/^hello/nihao/' xx.txt
   
2. nihao hello hello  
   
3.    hello  hello
   
4. nihao  hello hello
   
5. ##指定开头，行首的第一个字段必须是"hello",所以第二行的hello不能被匹配到。

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1. zouboan@hp:~/G/NuttX/apps/examples/elf/tests/errno$sed 's/^hello/nihao/g' xx.txt ##指定开头，加全局g,同上
   
2. nihao hello hello  
   
3.    hello  hello
   
4. nihao  hello hello

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