#!/bin/bash

function usage() {
cat <<__EOT__

Usage:
    $0 [-f filename]

Example:
    cat file1 | $0
    $0 < file1
    $0 -f file1

__EOT__
exit 1
}

if [ -p /dev/stdin ] || [ -f /dev/stdin ]; then
    d=$(cat /dev/stdin)
else
    while getopts f: OPT
    do
        case $OPT in
            f)  FILENAME=$OPTARG
                ;;
            \?) usage
                ;;
        esac
    done

    if [ -z $FILENAME ]; then
        usage
        exit 1
    fi

    if [ -f $FILENAME ]; then
        d=$(cat $FILENAME)
    else
        echo "Not found $FILENAME"
        usage
        exit 1
    fi
fi

echo "$d"