On 04/20/2017 11:51 AM, Assaf Gordon wrote: > If I may suggest the following sed program: > > $ cat file > a > b > c > bla1 > bla2 > UGLY > bla3 > bla4 > e > f > g > > $ sed -n ':x 1,2{N;bx} ; /UGLY/{ N;N;z;bx }; /./P;N;D' file
Works as long as lines 1 and 2 do not contain UGLY. But misbehaves if UGLY appears early: $ printf '2\nUGLY\n3\n4\nc\nd\n' | sed -n ':x 1,2{N;bx}; /UGLY/{N;N;z;bx}; /./P;N;D' d Oops - missed c. Also misbehaves if two occurrences of UGLY appear with overlapping context: $ printf 'a\nb\n1\n2\nUGLY\n3\nUGLY\n4\n5\nc\nd\n' | sed -n ':x 1,2{N;bx}; /UGLY/{N;N;z;bx}; /./P;N;D' a b 4 5 c d Oops - didn't filter 4 and 5. May be fixable with even more magic, perhaps by using the hold buffer to track the status of the last three lines, and suppressing output if any of the last three inputs were UGLY. But more complicated than I want to spend time on for the sake of this email. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
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