Introduce ot::shell_escape

src/opustags.h

@@ -34,6 +34,7 @@
 #include <memory>
 #include <optional>
 #include <string>
+#include <string_view>
 #include <vector>
 
 namespace ot {
@@ -165,6 +166,9 @@ private:
 	iconv_t cd; /**< conversion descriptor */
 };
 
+/** Escape a string so that a POSIX shell interprets it as a single argument. */
+std::string shell_escape(std::string_view word);
+
 /**
  * Execute the editor process specified in editor using execlp. Wait for the process to exit and
  * return st::ok on success, or st::child_process_failed if it did not exit with 0.

src/system.cc

@@ -137,6 +137,26 @@ ot::status ot::encoding_converter::operator()(const char* in, size_t n, std::str
 	return ot::st::ok;
 }
 
+std::string ot::shell_escape(std::string_view word)
+{
+	std::string escaped_word;
+	// Pre-allocate the result, assuming most of the time enclosing it in single quotes is enough.
+	escaped_word.reserve(2 + word.size());
+
+	escaped_word += '\'';
+	for (char c : word) {
+		if (c == '\'')
+			escaped_word += "'\\''";
+		else if (c == '!')
+			escaped_word += "'\\!'";
+		else
+			escaped_word += c;
+	}
+	escaped_word += '\'';
+
+	return escaped_word;
+}
+
 ot::status ot::run_editor(const char* editor, const char* path)
 {
 	pid_t pid = fork();

t/system.cc

@@ -49,10 +49,19 @@ void check_converter()
 	is(rc, ot::st::badly_encoded, "conversion from bad UTF-8 fails");
 }
 
+void check_shell_esape()
+{
+	is(ot::shell_escape("foo"), "'foo'", "simple string");
+	is(ot::shell_escape("a'b"), "'a'\\''b'", "string with a simple quote");
+	is(ot::shell_escape("a!b"), "'a'\\!'b'", "string with a bang");
+	is(ot::shell_escape("a!b'c!d'e"), "'a'\\!'b'\\''c'\\!'d'\\''e'", "string with a bang");
+}
+
 int main(int argc, char **argv)
 {
-	plan(2);
+	plan(3);
 	run(check_partial_files, "test partial files");
 	run(check_converter, "test encoding converter");
+	run(check_shell_esape, "test shell escaping");
 	return 0;
 }