With Bash, you can use printf with hex codes

\xHH   byte with hexadecimal value HH (1 to 2 digits)
\uHHHH Unicode (ISO/IEC 10646) character with hex value HHHH (4 digits)

example

$ printf '\x26'
&

However the Unicode example does not print as expected

$ printf '\u0026'
\u0026

My Bash version

$ echo $BASH_VERSION
4.1.10(4)-release
bash printf
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