But it's difficult to stop the linker from adding extra stuff, which is why I eventually specified the headers (and three addresses) by hand in the assembly file and stopped using a linker.
You may find some of the other tricks in the article helpful, but it might be hard to follow depending on your level of experience with assembly. My general advice would be that 'push' and 'pop' are your two best friends if you want to move around 64-bit values.
Why did you decide to build the string backward?
Instead of doing cmp $0, %eax, you can use test eax, eax - that's another low hanging fruit.
It seems that you could also preset a dedicated reg to 0 and another to 1, further shaving a few bytes.
I just hope that someone at some point figures out how to combine these two things, so we can pursue the best possible way of writing a program, and then prove it correct too. This would be a sort-of immortal program that would never need updating. Well, until it becomes obsolete because the world has changed around it.
base64 -d <<EOF > btry && chmod a+x btry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EOF
#!/usr/bin/env bash
# Print the remaining amount of energy (or charge)
# stored in the battery identified by `BAT0`. This
# is what works on my ThinkPad X220 and may not be
# portable to other laptops without changes.
cd /sys/class/power_supply/BAT0 || exit $?
# Sometimes there are `energy_now` and `energy_full`
# pseudofiles, and sometimes there are `charge_now`
# and `charge_full` pseudofiles instead.
if [[ -e energy_now ]]; then
now=$(<energy_now)
full=$(<energy_full)
unit=Wh
elif [[ -e charge_now ]]; then
now=$(<charge_now)
full=$(<charge_full)
unit=Ah
fi
percent=$((100 * now / full))
# Convert from microwatt-hours (or microampere-hours)
# to watt-hours (or ampere-hours).
now=$(bc <<< "scale=1; $now / 1000000")
full=$(bc <<< "scale=1; $full / 1000000")
echo "$now $unit / $full $unit (${percent}%)"