helper functions for formatting log output

log.sh

#!/usr/bin/env bash

# The logging functions all take input both as arguments and as stdin so that
# logging can be piped from other commands. The commands use this themselves:
# `log_sub` pipes into `log` which pipes into `prefix`.


prefix () {
    local replace="s/^/$1/"
    if (( $# > 1 )); then
        echo "${@:2}" | sed "$replace"
    else
        tee | sed "$replace"
    fi
}

log () {
    local date_fmt='--iso-8601=seconds'
    if (( $# > 0 )); then
        echo "$*" | prefix "[$(date ${date_fmt})] "
    else
        tee | prefix "[$(date ${date_fmt})] "
    fi
}

log_sub () {
    local p=" ---> "
    if (( $# > 0 )); then
        echo "$*" | prefix "$p" | log
    else
        tee | prefix "$p" | log
    fi
}