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# /usr/bin/perl ... ab c,ab c\,ab c/abc,ab cd,ab cd\,ab cd\x,ab c/abc ab cd\ab c,a+b,a+b/,a+b\abc,bar,bar\zot,\,/,\abc,/abc,\x,/x /\,\/,/\x,\/x
'abc' begins 'abc' 'abc' begins 'abc\' ... 'a+b' begins 'a+b' 'a+b' begins 'a+b/' 'a+b' begins 'a+b\abc'