First of all, exp isn't the same as 2^x (it's e^x). (Found that when I tested the code.)

#!/usr/bin/perl
use strict;
use warnings;

my %opts = (
    power => sub { exp( $_[0] )},
    log2  => sub { log( $_[0] )/log(2.0) },
    loge  => sub { log( $_[0] ) },
    log10 => sub { log( $_[0] )/log(10.0) },
    round => sub { int($_[0] + ($_[0] <=> 0)*0.5) },
    trunc => sub { int $_[0] },
    f1    => sub { sprintf "%.1f", $_[0] },
    f2    => sub { sprintf "%.2f", $_[0] },
    f3    => sub { sprintf "%.3f", $_[0] },
    f4    => sub { sprintf "%.4f", $_[0] },
    f5    => sub { sprintf "%.5f", $_[0] },
);                                                              

my $func = sub {$_[0]};
for my $arg (reverse @ARGV){
    if (defined $opts{$arg}){
        my $localfunc = $func;
        $func = sub {$opts{$arg}->($localfunc->($_[0]))};
    } else {
        print STDERR "Unknown arg: $arg\n";
    }
}

while (<> ) {
        chomp;
        my @in = split;
        print shift(@in), " ";
        print join(" ", map { $func->($_) } @in), "\n";
}
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