Binary to Decimal:
perl -e 'for(split//,$ARGV[0]){$t+=$_;$t=$t<<1};$t=$t>>1;print "$t\n"' 101010

Decimal to Binary:
perl -e '$t=$ARGV[0];do{push@b,$t%2;$t=$t>>1}until($t==0);print reverse"\n",@b' 42