Function SetVariable

src/bin/psql/variables.c:210–296

* Set the variable named "name" to value "value", * or delete it if "value" is NULL. * * Returns true if successful, false if not; in the latter case a suitable * error message has been printed, except for the unexpected case of * space or name being NULL. */

 * space or name being NULL.
 */
bool
SetVariable(VariableSpace space, const char *name, const char *value)
{
	struct _variable *current,
			   *previous;

	if (!space || !name)
		return false;

	if (!valid_variable_name(name))
	{
		/* Deletion of non-existent variable is not an error */
		if (!value)
			return true;
		pg_log_error("invalid variable name: \"%s\"", name);
		return false;
	}

	for (previous = space, current = space->next;
		 current;
		 previous = current, current = current->next)
	{
		int			cmp = strcmp(current->name, name);

		if (cmp == 0)
		{
			/*
			 * Found entry, so update, unless assign hook returns false.
			 *
			 * We must duplicate the passed value to start with.  This
			 * simplifies the API for substitute hooks.  Moreover, some assign
			 * hooks assume that the passed value has the same lifespan as the
			 * variable.  Having to free the string again on failure is a
			 * small price to pay for keeping these APIs simple.
			 */
			char	   *new_value = value ? pg_strdup(value) : NULL;
			bool		confirmed;

			if (current->substitute_hook)
				new_value = current->substitute_hook(new_value);

			if (current->assign_hook)
				confirmed = current->assign_hook(new_value);
			else
				confirmed = true;

			if (confirmed)
			{
				if (current->value)
					pg_free(current->value);
				current->value = new_value;

				/*
				 * If we deleted the value, and there are no hooks to
				 * remember, we can discard the variable altogether.
				 */
				if (new_value == NULL &&
					current->substitute_hook == NULL &&