Convert an .ics calendar file into JSON syntax

ics2json.sh

#! /usr/bin/env bash
#>------------------------------------------------------------------------------
#>
#> [ ics2json ]
#>
#> ABOUT:
#>
#>    Convert an .ics calendar file into JSON syntax
#>
#>    If input data is passed as a file reference, output data is written to
#>    an identically named file as the input file with a new file extension
#>    of ".json".
#>
#>    If input data is passed as an incoming pipe, then output data will be
#>    printed directly the standard output.
#>
#>    Created on 20201209 by h8rt3rmin8r ([email protected])
#>
#> USAGE:
#>
#>    ics2json <INPUT>
#>    ics2json <OPTION>
#>
#>    where "INPUT" is a valid file reference which includes the file extension
#>    ".ics"; and where "OPTION" is one of the following:
#>
#>                 |
#>    -h, --help   | Print this help text to the terminal
#>                 |
#>
#> SOURCE:
#>
#>    # Pastebin
#>    https://bit.ly/2W6PVox
#>
#>    # Github
#>    https://bit.ly/377V323
#>
#>------------------------------------------------------------------------------
#-------------------------------------------------------------------------------
# Declare functions

function ics2json_help() {
    # Script help text printing function

    cat "${0}" \
        | grep -E '^#>' \
        | sed 's/^..//'

    return $?
}

function ics2json_vbs() {
    # General script verbosity function

    local message="$@"
    local timestamp="$(date '+%s%N')"
    
    echo "${timestamp}|${sh_name}|${message}" &>${vb_x}

    return $?
}

function _main() {
    dos2unix \
        | sed 's/:/█/;s/$/░/' \
        | tr -d '\n' \
        | tr '\t' ' ' \
        | tr -s ' ' ' ' \
        | sed -E 's/BEGIN█/\nBEGIN█/g' \
        | tail -n +2 \
        | sed 's/\"/\\\"/g;s/█/\":\"/g;s/░/\",\"/g;s/^/\{\"/;s/..$/\},/' \
        | tr -d '\n' \
        | sed 's/^/\[/;s/,$//;s/$/\]/' \
        | jq -c '.' 2>/dev/null
    
    local e_c="$?"

    if [[ "${e_c}" -ne 0 ]]; then
        echo '[]'
    fi

    return ${e_c}
}

#-------------------------------------------------------------------------------
# Declare variables and execute operations

vb_x="/dev/stderr"
sh_name="ics2json"

## catch help text requests

if [[ "${1}" =~ ^[-][hH]$ || "${1}" =~ ^[-]+help$ ]]; then
    ics2json_help
    
    exit $?
fi

## execute operations based upon the form of input detected

if [ -t 0 ]; then

    ## declare input-specific variables

    i_n=$(readlink -f "${1}")
    out_file="${i_n%.ics}.json"
    is_present=$(egrep --quiet '^.' <<<"${1}"; echo $?)
    is_file=$(if [[ -f "${i_n}" ]]; then echo "0"; else echo "1"; fi)
    is_ics=$(if [[ "${i_n}" =~ .ics$ ]]; then echo "0"; else echo "1"; fi)

    ## test the input string

    if [[ "${is_present}" -ne 0 ]]; then
        ics2json_vbs "ERROR: No input detected"
        ics2json_vbs "Requires: <FILE>.ics"
        ics2json_vbs "Use '--help' for more information"
        
        exit 1
    fi

    if [[ "${is_file}" -ne 0 ]]; then
        ics2json_vbs "ERROR: Input is not a valid file reference: ${1}"
        ics2json_vbs "Use '--help' for more information"
        
        exit 1
    fi

    if [[ "${is_ics}" -ne 0 ]]; then
        ics2json_vbs "ERROR: Input is not a valid '.ics' file: ${1}"
        ics2json_vbs "Use '--help' for more information"
        
        exit 1
    fi

    _main <"${i_n}" > "${out_file}"

    e_c="$?"

    echo "${out_file}"
else
    _main

    e_c="$?"
fi

exit ${e_c}

Why do you use
if [ -t 0 ]; then?
Do you see any issues using
if [ -n "${1}" ]; then
to be able to call the script from an automation script?