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(a) SED Given a file, replace all the sequences of 4 or more digits with the word "cat".

(b) GREP Given a file, display all the lines starting with the word "cat" and ending with the word "mouse".

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You should at least make an effort to do your homework before asking for help. –  jordanm Apr 8 '13 at 16:02
Please ask one question per question. –  N.N. Apr 8 '13 at 16:13
Or at least try to make it look a little less like a homework assignment. –  Shadur Apr 8 '13 at 18:16
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closed as too localized by derobert, Ulrich Dangel, Renan, vonbrand, jasonwryan Apr 8 '13 at 18:08

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1 Answer

a) sed 's/[0-9]\{4,\}/cat/g'

s=substitute, [0-9]=range of numbers, \{4,\}=4 or more occurrences, g=global - i.e. for all matching occurrences, not just the first match on each line

b) grep '^cat.*mouse$'

^=beginning of the line, .=any character, *=0,1 or more occurrences of previous (here .), $=the end of the line

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