purl - call knitr::purl() in Linux terminal

#!/bin/bash

# http://stackoverflow.com/questions/402377/
# using-getopts-in-bash-shell-script-to-get-long-and-short-command-line-options

OPTIONS=$@
OPTNUM=$#

_usage() {
    cat <<EOF
purl $OPTIONS
$*
    Usage:    purl <[options]> file

      file
        Is a filename with extension *.Rmd or *Rnw.

    Options:

      -h  --help          Show this message
      -n  --noheaders     Remove chunk headers
      -o  --output=...    Set an output filename or sulfix

    Example:

      purl

EOF
}

if [ $# = 0 ]
then
    _usage
    exit 1
fi

TEMP=`getopt -o hno: --long help,noheaders,output: -n 'purl' -- "$@"`

if [ $? != 0 ]
then
    echo "Terminating." >&2
    exit 1
fi

eval set -- "$TEMP"

NOHEADER=false
OUTPUT=
while true; do
    case "$1" in
        -h | --help )
            _usage
            break
            ;;
        -n | --noheaders )
            NOHEADER=true
            shift
            ;;
        -o | --output )
            OUTPUT="$2"
            shift 2
            ;;
        -- )
            shift
            break
            ;;
        * )
            _usage
            break
            ;;
    esac
done

FILELIST=$@

SULFIX=
if [ $# -gt 1 ]
then
    echo "Number of files is greater than one so $OUTPUT will be used as sulfix."
    SULFIX=$OUTPUT
fi

for INPUT in $FILELIST;
do
    if [ ! -f "$INPUT" ]
    then
        echo "$INPUT doesn't exists."
        continue
    fi

    if [ -z "$OUTPUT" ]
    then
        OUTPUT="${INPUT%.*}.R"
    else
        OUTPUT="${INPUT%.*}$SULFIX.R"
    fi

    case "$INPUT" in
        *.Rmd | *.Rnw )
            echo
            echo "Running knitr::purl(\"$INPUT\", output=\"$OUTPUT\")."
            echo
            Rscript -e "require(knitr); purl(\"$INPUT\", output=\"$OUTPUT\")"
            ;;
        *)
            echo "The file $INPUT has a non supported file extension."
            exit 1
            ;;
    esac

    if [[ "$NOHEADER" == "true" ]]
    then
        echo
        echo "Removing chunk headers in the $OUTPUT file."
        echo
        grep -Ev '## ----' $OUTPUT > .aux
        cat -s .aux > $OUTPUT
        rm .aux
    fi
    echo
    echo
done