Regexp matches string and return only matched or group

match.sh

# String matcher for shell
# author: Vinícius Daniel Antunes Oliveira <viniciusdaniel@gmail.com>
# license: MIT <https://opensource.org/licenses/MIT>
#
#!/bin/bash
# Usage: 
#   cat /tmp/file | match.sh <regexp> [group match]
#   match.sh <filename> <regexp> [group match]
#   match.sh <string> <regexp> [group match]
#
#
# Receive pipe redirect
if [ ! -t 0 ] ; then 
  REGEX=$1;
  TEXT=$(</dev/stdin); 
  if [ -z "$2" ]; then
    GROUP=0;
  else
    GROUP=$2;
  fi
else
  INPUT=$1
  REGEX=$2;
  if [ -z "$3" ]; then
    GROUP=0;
  else
    GROUP=$3;
  fi

  # Read file or by pass string
  if [ -f "${INPUT}" ]; then 
    TEXT=$(<$INPUT);    
  else
    TEXT=$INPUT;
  fi
fi

[[ $TEXT =~ $REGEX ]] && [[ ! -z "${BASH_REMATCH[${GROUP}]}" ]] && echo "${BASH_REMATCH[${GROUP}]}"

Usage:

cat /tmp/file | match.sh <regexp> [group match]

OR

match.sh <filename> <regexp> [group match]

OR

match.sh <string> <regexp> [group match]