sed命令的"指定开头"和全局匹配
zouboan@hp:~/G/NuttX/apps/examples/elf/tests/errno$ cat xx.txt##xx.txt的内容hello hello hello
hellohello
hellohello hello
zouboan@hp:~/G/NuttX/apps/examples/elf/tests/errno$ sed 's/hello/nihao/' xx.txt
nihao hello hello
nihaohello
nihaohello hello
##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
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
nihao nihao nihao
nihaonihao
nihaonihao nihao
zouboan@hp:~/G/NuttX/apps/examples/elf/tests/errno$sed 's/^hello/nihao/' xx.txt
nihao hello hello
hellohello
nihaohello hello
##指定开头，行首的第一个字段必须是"hello",所以第二行的hello不能被匹配到。
zouboan@hp:~/G/NuttX/apps/examples/elf/tests/errno$sed 's/^hello/nihao/g' xx.txt ##指定开头，加全局g,同上
nihao hello hello
hellohello
nihaohello hello
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