#!/usr/bin/env bash

#
# tl(1): Tag lines from files or stdin with a string prefix or suffix before
# writing them to stdout. Specifying neither prefix nor suffix is acceptable,
# in which case the stream is simply reproduced on stdout, acting like cat(1).
#
# Option -h gives help. Specify a prefix with -p, and/or a suffix with -s. If
# no file arguments are given, defaults to reading standard input.
#
# Author: Tom Ryder <tom@sanctum.geek.nz>
# Copyright: 2016
# License: Public domain
#

# Name self
self=tl

# Define usage function
usage() {
    printf 'USAGE: %s [-h] [-p PREFIX] [-s SUFFIX] [--] [FILE1 FILE2 ...]\n' "$self"
}

# Start with empty prefix/suffix, or use the environment variables
prefix=$TL_PREFIX
suffix=$TL_SUFFIX

# Parse options out, give help if necessary
while getopts 'hp:s:' opt ; do
    case $opt in

        # -h: Print help
        h)
            usage
            exit
            ;;

        # -p: Specify prefix
        p)
            prefix=$OPTARG
            ;;

        # -s: Specify suffix
        s)
            suffix=$OPTARG
            ;;

        # Unknown option
        \?)
            usage >&2
            exit 2
            ;;
    esac
done
shift "$((OPTIND-1))"

# Need at least one tag
if ! (($#)) ; then
    set /dev/stdin
fi

# Print each line as we read it, prepending the tags, separated by spaces
for file in "$@" ; do
    while IFS= read -r line ; do
        printf '%s%s%s\n' "$prefix" "$line" "$suffix"
    done < "$file"
done