in reply to How do I modify a single line in a file?

Don't know if this is in one of the above references...
Anyway maybe from the commandline: 
perl -p -i -e ' s/whatever/whateverelse/ if /whateveryou'relookingfor/
+ ' /etc/passwd

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--the good, the bad and the physi--
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In Section Seekers of Perl Wisdom