Too much code. ;) 
perl -pi.bak -e'BEGIN{$/=\1024}($_,$/)=(undef,"\n")if ref$/' file.txt

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Just change 1024 to whatever byte size you want ... you do have to have that much memory available, but the rest is line by line.

UPDATE:
merlyn shared a better version in the CB shortly after i posted: 

perl -pi.bak -e'BEGIN{$/=\1024}($_,$/)=()if 1..1' file.txt

[download]
Reading the rest line by line is unecessary. Thanks again merlyn! :)

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

In reply to Re: Truncate the front of a file by jeffa
in thread Truncate the front of a file by flocto

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