#!perl

use 5.12.0;
use warnings;

my $sought = q{sb1 1.0 142r};
my $last;

while (my $line = <DATA>) {
    chomp $line;
    if ($line eq $sought) {
        $last =~ s{ \s+ \S+ \s* \z }{}msx;
    }
    say $last if $. > 1;
    $last = $line;
}
say $last;

__DATA__
pre 2
pre 1
4.62399E+09 2.90871E+09 7.17338E+14 
sb1 1.0 142r
post 1
post 2

##</code><code>##

$ match_exp_prob.pl
pre 2
pre 1
4.62399E+09 2.90871E+09
sb1 1.0 142r
post 1
post 2