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  • \n most certainly does have a meaning in a regex, try printf "aa\nbb" | perl -ne 'print if /\n/', that will only match aa\n and skips the bb for example. There do seem to be differences in implementation though cause grep -P won't match that. But how is $ relevant here? I want to match a literal newline, $ matches even in the absence of one: printf "aa" | grep 'a$' Commented Mar 10, 2014 at 17:17
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    @terdon \n has no special meaning, even in Perl regular expressions. It does, however, have special meaning in interpolated perl strings, of which qr// is one type. Search for \n in man perlre... Commented Mar 10, 2014 at 17:20
  • @derobert fair point, I expressed myself badly. I meant that \n matches newlines in regular expressions. You and babaslovesyou are quite right that it has no special meaning as such, I just mean that is is "matchable" . Commented Mar 10, 2014 at 17:22
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    @terdon Well, except you're trying to match the character 0x0A (newline), and you're trying to do it with the character sequence 0x5C (backslash) 0x6E (n). Since \n has no special meaning, it tries to match itself. The \ may or may not get stripped out (invalid escape) depending on RE engine, but you're trying to match <NL> vs \n or n, neither matches. Commented Mar 10, 2014 at 17:27
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    @terdon in your Perl example, what's actually happening is that the string parsing is turning \n into <NL>, before passing it off to the regexp engine. That's a feature of Perl string parsing. Commented Mar 10, 2014 at 17:28