--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/relpipe-data/examples/rdf-sparql-interpreter.sh	Mon Jul 27 17:51:53 2020 +0200
@@ -0,0 +1,65 @@
+#!/bin/bash
+
+# Relational pipes
+# Copyright © 2020 František Kučera (Frantovo.cz, GlobalCode.info)
+# 
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, version 3 of the License.
+# 
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+
+# This is a helper script that could be used as a shebang interpreter for SPARQL files.
+# Just set the SPARQL file executable and add the first line comment.
+# The endpoint and relation parameters are optional.
+# Parameters must be at the beginning of the file before any empty lines.
+# Only the first occurrence of each parameter is relevant.
+# This interpreter produces a human-readable table if STDOUT is a terminal
+# and machine-readable relational data if STDOUT is not a terminal.
+# So the stream can be piped to any relational transformation (e.g. relpipe-tr-sql)
+# or output filter (e.g. relpipe-out-csv).
+#
+# Example:
+#
+#	#!/usr/bin/env rdf-sparql-interpreter.sh
+#	# endpoint: https://query.wikidata.org/sparql
+#	# relation: few_statements
+#	
+#	SELECT * WHERE { ?subject ?predicate ?object } LIMIT 3
+
+
+# Execute the SPARQL query and send the results to the STDOUT
+# either raw or formatted as a table depending on whether STDOUT is a terminal or not.
+interpret_sparql() {
+	if [ -t 1 ] ; then relpipe-in-sparql "$@" | relpipe-out-tabular;
+	else relpipe-in-sparql "$@"; fi
+}
+
+# Fetches the parameter $2 from file $1.
+# Parameters must be formatted as comments: „# name: value“.
+# Only the first occurrence is relevant. And empty line terminates processing.
+find_parameter() {
+	perl -e 'while(<>) { if (/^\s*$/) { last; } elsif (/^# ($ARGV[0]): (.*)$/) { print "$2"; last; } }' "$1" "$2"
+}
+
+# Appends the "${options[@]}" array with option $2 taken from the $1 file
+# or from environmental variable RELPIPE_IN_SPARQL_${2^^} (the variable has precedence).
+prepare_option() {
+	variableName="RELPIPE_IN_SPARQL_${2^^}"
+	parameterName="$2"
+	[[ -n "${!variableName}" ]] && value="${!variableName}" || value="$(find_parameter "$1" "$parameterName")"
+	[[ -n "$value" ]] && options+=("--$parameterName" "$value")
+}
+
+options=()
+prepare_option "$1" endpoint
+prepare_option "$1" relation
+
+cat "$1" | interpret_sparql "${options[@]}"