1 #!/bin/bash

     2 

     3 # Relational pipes

     4 # Copyright © 2020 František Kučera (Frantovo.cz, GlobalCode.info)

     5 # 

     6 # This program is free software: you can redistribute it and/or modify

     7 # it under the terms of the GNU General Public License as published by

     8 # the Free Software Foundation, version 3 of the License.

     9 # 

    10 # This program is distributed in the hope that it will be useful,

    11 # but WITHOUT ANY WARRANTY; without even the implied warranty of

    12 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

    13 # GNU General Public License for more details.

    14 # 

    15 # You should have received a copy of the GNU General Public License

    16 # along with this program. If not, see <http://www.gnu.org/licenses/>.

    17 

    18 

    19 # This is a helper script that could be used as a shebang interpreter for SPARQL files.

    20 # Just set the SPARQL file executable and add the first line comment.

    21 # The endpoint and relation parameters are optional.

    22 # Parameters must be at the beginning of the file before any empty lines.

    23 # Only the first occurrence of each parameter is relevant.

    24 # This interpreter produces a human-readable table if STDOUT is a terminal

    25 # and machine-readable relational data if STDOUT is not a terminal.

    26 # So the stream can be piped to any relational transformation (e.g. relpipe-tr-sql)

    27 # or output filter (e.g. relpipe-out-csv).

    28 #

    29 # Example:

    30 #

    31 #	#!/usr/bin/env rdf-sparql-interpreter.sh

    32 #	# endpoint: https://query.wikidata.org/sparql

    33 #	# relation: few_statements

    34 #	

    35 #	SELECT * WHERE { ?subject ?predicate ?object } LIMIT 3

    36 

    37 

    38 # Execute the SPARQL query and send the results to the STDOUT

    39 # either raw or formatted as a table depending on whether STDOUT is a terminal or not.

    40 interpret_sparql() {

    41 	if [ -t 1 ] ; then relpipe-in-sparql "$@" | relpipe-out-tabular;

    42 	else relpipe-in-sparql "$@"; fi

    43 }

    44 

    45 # Fetches the parameter $2 from file $1.

    46 # Parameters must be formatted as comments: „# name: value“.

    47 # Only the first occurrence is relevant. And empty line terminates processing.

    48 find_parameter() {

    49 	perl -e 'while(<>) { if (/^\s*$/) { last; } elsif (/^# ($ARGV[0]): (.*)$/) { print "$2"; last; } }' "$1" "$2"

    50 }

    51 

    52 # Appends the "${options[@]}" array with option $2 taken from the $1 file

    53 # or from environmental variable RELPIPE_IN_SPARQL_${2^^} (the variable has precedence).

    54 prepare_option() {

    55 	variableName="RELPIPE_IN_SPARQL_${2^^}"

    56 	parameterName="$2"

    57 	[[ -n "${!variableName}" ]] && value="${!variableName}" || value="$(find_parameter "$1" "$parameterName")"

    58 	[[ -n "$value" ]] && options+=("--$parameterName" "$value")

    59 }

    60 

    61 options=()

    62 prepare_option "$1" endpoint

    63 prepare_option "$1" relation

    64 

    65 cat "$1" | interpret_sparql "${options[@]}"