From owner-freebsd-questions@freebsd.org Wed Nov 8 13:42:34 2017 Return-Path: Delivered-To: freebsd-questions@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 19A6EE53D9B for ; Wed, 8 Nov 2017 13:42:34 +0000 (UTC) (envelope-from freebsd@edvax.de) Received: from mailrelay15.qsc.de (mailrelay15.qsc.de [212.99.187.254]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "*.antispameurope.com", Issuer "TeleSec ServerPass Class 2 CA" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 8399D7B3D4 for ; Wed, 8 Nov 2017 13:42:32 +0000 (UTC) (envelope-from freebsd@edvax.de) Received: from mx01.qsc.de ([213.148.129.14]) by mailrelay15.qsc.de; Wed, 08 Nov 2017 14:42:30 +0100 Received: from r56.edvax.de (port-92-195-23-159.dynamic.qsc.de [92.195.23.159]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mx01.qsc.de (Postfix) with ESMTPS id 8A19F3CC3F; Wed, 8 Nov 2017 14:42:29 +0100 (CET) Received: from r56.edvax.de (localhost [127.0.0.1]) by r56.edvax.de (8.14.5/8.14.5) with SMTP id vA8DgSLO002719; Wed, 8 Nov 2017 14:42:28 +0100 (CET) (envelope-from freebsd@edvax.de) Date: Wed, 8 Nov 2017 14:42:28 +0100 From: Polytropon To: Arthur Chance Cc: freeBSD Mailing List Subject: Re: how to code a timer loop in a sh script Message-Id: <20171108144228.eeb81eaa.freebsd@edvax.de> In-Reply-To: <95cc2469-955e-02c1-3cdd-82e630feaa1c@qeng-ho.org> References: <5A00A826.2000501@gmail.com> <20171108135659.dab81adf.freebsd@edvax.de> <95cc2469-955e-02c1-3cdd-82e630feaa1c@qeng-ho.org> Reply-To: Polytropon Organization: EDVAX X-Mailer: Sylpheed 3.1.1 (GTK+ 2.24.5; i386-portbld-freebsd8.2) Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-cloud-security-sender: freebsd@edvax.de X-cloud-security-recipient: freebsd-questions@freebsd.org X-cloud-security-Virusscan: CLEAN X-cloud-security-disclaimer: This E-Mail was scanned by E-Mailservice on mailrelay15.qsc.de with EA7776E4696 X-cloud-security-connect: mx01.qsc.de[213.148.129.14], TLS=1, IP=213.148.129.14 X-cloud-security: scantime:.1637 X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 08 Nov 2017 13:42:34 -0000 On Wed, 8 Nov 2017 13:23:14 +0000, Arthur Chance wrote: > On 08/11/2017 12:56, Polytropon wrote: > > On Wed, 8 Nov 2017 08:25:55 +0100 (CET), Trond Endrest=F8l wrote: > >> On Mon, 6 Nov 2017 19:24+0100, Michael Schuster wrote: > >> > >>> while [ 1 ]; do > >>> do_stuff > >>> sleep 600 > >>> done > >> > >> This should be even better: > >> > >> while true; do > >> do_stuff > >> sleep 600 > >> done > >=20 > > Yes. > >=20 > > While /usr/bin/true always evaluates to true (as desired), > > "test 1" depends on if it's an internal or external command > > which depends on the shell, and if the implementation conforms > > to the standard. In this specific case, 1 would be seen as "1", > > a non-empty string, and therefore should cause test to return 0, > > as a non-empty string evaluates to true. > >=20 > > From "man test": > >=20 > > string True if string is not the null string. > >=20 > > As the 1 is the only expression tested, this rule applies. > > No math included. ;-) >=20 > A minor point: in /bin/sh "true" and "test" are builtins (with synonyms > ":" and "[" respectively). true (and :) don't need to test anything, so > shave microseconds off the 10 minute sleep cycle. :-) That's correct (at least in FreeBSD's /bin/sh; other implementations might not have those as builtins - in case script portability should be important here). I still agree with you that true or : aren't as "heavy on resources" as test (either as builtin or external program call); as if anyone cares for efficiency today... ;-) --=20 Polytropon Magdeburg, Germany Happy FreeBSD user since 4.0 Andra moi ennepe, Mousa, ...