Convert decimal to hexadecimal in UNIX shell script

Tried printf(1)?

printf "%x\n" 34
22

There are probably ways of doing that with builtin functions in all shells but it would be less portable. I've not checked the POSIX sh specs to see whether it has such capabilities.

bash-4.2$ printf '%x\n' 4294967295
ffffffff

bash-4.2$ printf -v hex '%x' 4294967295
bash-4.2$ echo $hex
ffffffff

Hexidecimal to decimal:

$ echo $((0xfee10000))
4276158464

Decimal to hexadecimal:

$ printf '%x\n' 26
1a

echo "obase=16; 34" | bc

If you want to filter a whole file of integers, one per line:

( echo "obase=16" ; cat file_of_integers ) | bc