awk replace code example

Example 1: sed replace

For using match in sed replacement, just border it with '\(' and '\)':
echo Before123 | sed 's/Before\([0-9]*\)/\1After/g'
123After	# number is matched withtin '\( \)' and replaced in '\1'
Example with 2 match replacements
echo a_b | sed 's/\(^.*\)_\(.*$\)/first is \1 and \2 is after/g'

Example 2: awk delimiter replace

Just use tr command as follows to replace a delimiter:
tr '(' '[' file.txt #replaces parenthesis '(' for brackets '['
tr '()' '[]' file.xt #respectively replaces '(' for '[' and ')' for ']'