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If you don't mind reading the source file twice and a whole lot of random seeks the second time through, you can generate a list of offsets, shuffle those and then loop through a seek, read, write cycle:
#!/usr/bin/perl use strict; use warnings; use List::Util qw(shuffle); my @offsets; print STDERR "Scanning..."; open(IN, $ARGV[0]); do { push @offsets, tell(IN) } while (<IN>); close(IN); pop @offsets; print STDERR "Done. ($#offsets)\nScrambling..."; @offsets = shuffle(@offsets); print STDERR "Done.\nWriting scrambled..."; open(IN, $ARGV[0]); for (@offsets) { seek(IN, $_, 0); my $line = <IN>; $line .= $/ if $line !~ qr{$/}; print $line; } print STDERR "Done.\n";
This scrambled an 800k line/60M file I had handy in eight seconds with minimal memory usage in process space. I assume the kernel kept the entire file cached in memory.

In reply to Re: mem usage by crag
in thread mem usage by halfcountplus

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