in reply to Remove all lines, except those starting with pattern

Two problems:
  1. The parentheses around (?!...) aren't optional.
  2. Look-around assertions are zero-width, i.e. if they match, they don't consume any part of the string. It means replacing them doesn't remove anything.
To remove the first line, you'd be better off with 
perl -ne 'print if 1 != $.'

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$. is the current line number of the last accessed file handle.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,

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