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grep lookbehind，锚定意外结果

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grep lookbehind，锚定意外结果,grep,gnu,Grep,Gnu,为什么这个锚定的lookbehinnd断言不能像预期的那样工作 $ grep -Po '^(?<=field_one: ).*' <<< "field_one: 123" # no match. non-zero exit. why? $ grep -Po '(?<=field_one: ).*' <<< "field_one: 123" # match, no anchor 123 $ grep -Po '(?<=^field_one:

为什么这个锚定的lookbehinnd断言不能像预期的那样工作

$ grep -Po '^(?<=field_one: ).*' <<< "field_one: 123" # no match. non-zero exit. why?

$ grep -Po '(?<=field_one: ).*' <<< "field_one: 123"  # match, no anchor
123
$ grep -Po '(?<=^field_one: ).*' <<< "field_one: 123" # match, anchor inside lookbehind
123
$ grep -Po '^(field_one: ).*' <<< "field_one: 123"    # match, no lookbehind
field_one: 123

$grep-Po'^（？你不能期望
^（？）？

grep -Po '(?<=^field_one: ).*' <<< "field_one: 123"



grep -Po '^field_one:\s*\K.*' <<< "field_one: 123"
                     ^^^^^