taking substrings bash code example

Example 1: how to print substring in bash script

INPUT='someletters_12345_moreleters.ext'
SUBSTRING=$(echo $INPUT| cut -d'_' -f 2)
echo $SUBSTRING

Example 2: substring in shell script

STR="birthday-091216-pics"
SUBSTR=$(echo $STR | cut -d'-' -f 2)
echo $SUBSTR