re = /^(?:[0-9A-Fa-f]+\s+){1,4}/m
str = 'A92 6100 011E Bsr P6
A96 43EE 003A Lea.L $3A(A6), A1
A9A 6100 013E Bsr P8
A9E 6608 BNE.B L90
AA0 4E91 Jsr (A1)
AA2 70F5 MoveQ.L #$-B, D0
AA4 6100 010C Bsr P6
AA8 43F8 0AD8 L90: Lea.L (SysResName), A1
AAC 76FF MoveQ.L #$-1, D3
AAE 6100 012C Bsr P9
AB2 6600 0004 BNE L91
AB6 4E91 Jsr (A1)
AB8 21F8 02A6 02B2 L91: Move.L (SysZone), (RAMBase)
ABE 700C MoveQ.L #$C, D0
AC0 A722 _NewHandleSysClear
AC2 21C8 0AEC Move.L A0, (AppParmHandle)
AC6 A02C _InitApplZone
AC8 A04F _RDrvrInstall
ACA 2F05 Move.L D5, -(A7)'
subst = ''
result = str.gsub(re, subst)
# Print the result of the substitution
puts result
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Ruby, please visit: http://ruby-doc.org/core-2.2.0/Regexp.html