From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=0.5 required=5.0 tests=DKIM_INVALID,DKIM_SIGNED, MAILING_LIST_MULTI,RCVD_IN_DNSWL_NONE,RDNS_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.2 Received: (qmail 10395 invoked from network); 11 Mar 2020 02:48:19 -0000 Received-SPF: pass (minnie.tuhs.org: domain of minnie.tuhs.org designates 45.79.103.53 as permitted sender) receiver=inbox.vuxu.org; client-ip=45.79.103.53 envelope-from= Received: from unknown (HELO minnie.tuhs.org) (45.79.103.53) by inbox.vuxu.org with ESMTP; 11 Mar 2020 02:48:19 -0000 Received: by minnie.tuhs.org (Postfix, from userid 112) id AA69E9BBFE; Wed, 11 Mar 2020 12:48:13 +1000 (AEST) Received: from minnie.tuhs.org (localhost [127.0.0.1]) by minnie.tuhs.org (Postfix) with ESMTP id 538069BB47; Wed, 11 Mar 2020 12:47:45 +1000 (AEST) Authentication-Results: minnie.tuhs.org; dkim=fail reason="signature verification failed" (1024-bit key; secure) header.d=tnetconsulting.net header.i=@tnetconsulting.net header.b="A+5wpy/d"; dkim-atps=neutral Received: by minnie.tuhs.org (Postfix, from userid 112) id E10769BB47; Wed, 11 Mar 2020 12:47:42 +1000 (AEST) Received: from tncsrv06.tnetconsulting.net (tncsrv06.tnetconsulting.net [45.33.28.24]) by minnie.tuhs.org (Postfix) with ESMTPS id 936F79BB46 for ; Wed, 11 Mar 2020 12:47:41 +1000 (AEST) Received: from Contact-TNet-Consulting-Abuse-for-assistance by tncsrv06.tnetconsulting.net (8.15.2/8.15.2/Debian-3) with ESMTPSA id 02B2lcwp022327 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NO) for ; Tue, 10 Mar 2020 21:47:40 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=tnetconsulting.net; s=2019; t=1583894860; bh=Pjtkyqb1H7drxTx/pTbQYn+IWlSo9rzp1xwx0hIxglY=; h=Subject:To:References:From:Message-ID:Date:User-Agent: MIME-Version:In-Reply-To:Content-Type:Cc:Content-Disposition: Content-Language:Content-Transfer-Encoding:Content-Type:Date:From: In-Reply-To:Message-ID:MIME-Version:References:Reply-To: Resent-Date:Resent-From:Resent-To:Resent-Cc:Sender:Subject:To: User-Agent; b=A+5wpy/dfWgEN4r325F1SG9LGKJwlTviPpv5u/TInHtBL8bzOfznEXKc8D2USiggz 4kf7M6xsfJnjhTCNc5H0O7bweS0U5wLhzhSExznvoj27kIkabxaKSUz2def6B2ERyw Ma665jyCeHrCJZvKkiOFw5UYp37TYZM5vGygzpgk= To: tuhs@minnie.tuhs.org References: <20200306224431.D226C18C080@mercury.lcs.mit.edu> <1fab6a1a-ccfb-02cc-c23e-1a0d8c9e954a@spamtrap.tnetconsulting.net> <202003100729.02A7Tsg0002007@freefriends.org> Organization: TNet Consulting Message-ID: <4fb5b7ab-03a4-df64-d25b-8be587b6a17b@spamtrap.tnetconsulting.net> Date: Tue, 10 Mar 2020 20:47:39 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.2 MIME-Version: 1.0 In-Reply-To: <202003100729.02A7Tsg0002007@freefriends.org> Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-256; boundary="------------ms080302010505000402070804" Subject: Re: [TUHS] First appearance of named pipes X-BeenThere: tuhs@minnie.tuhs.org X-Mailman-Version: 2.1.26 Precedence: list List-Id: The Unix Heritage Society mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Grant Taylor via TUHS Reply-To: Grant Taylor Errors-To: tuhs-bounces@minnie.tuhs.org Sender: "TUHS" This is a cryptographically signed message in MIME format. --------------ms080302010505000402070804 Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 3/10/20 1:29 AM, arnold@skeeve.com wrote: > Absolutely: >=20 > $ mkfifo the_fifo > $ ls -l the_fifo > prw-rw-r-- 1 arnold arnold 0 Mar 10 09:28 the_fifo > $ echo foo > the_fifo & sleep 1 ; cat the_fifo > [1] 3721 > foo > [1]+ Done echo foo > the_fifo >=20 > As you stated, not that you'd want to do that, but you can. Thank you for your reply Arnold. As I was reading your reply, I realized that I did not fully convey the=20 question that I was still mulling over in my head. (More in a moment.) This thread is one of about three things happening in my life that have=20 to do with pipes, FIFOs, and file descriptors. I managed to articulate=20 the simpler of the questions while reading Noel's email. The larger more onerous question is could I leverage exec to alter where = file descriptors 0 (STDIN), 1 (STDOUT), and 2 (STDERR) are set to,=20 including changing 1 to the value of a FIFO, and 0 of a subsequent=20 command to also be the value of the FIFO, thus have pipe like behavior=20 between two commands without using a pipe or redirection as in ">". This has also gotten me to wonder about the possibility of having=20 multiple commands output to a file descriptor; 1 / 2 / other, that is=20 input to a separate command. Sort of the opposite of tee, in a manner=20 of speaking. I'll try to articulate: $ mkfifo test.fifo $ exec 3>&1 $ exec 1> test.fifo $ for l in {a..z}; do echo $l; sleep 1; done & $ for L in {A..Z}; do echo $L; sleep 1; done & $ for n in {1..100}; do echo $n; sleep 1; done & $ exec 1>&3 $ cat test.fifo This seems special to me in that I have three processes (for loops)=20 writing into what is effectively the same pipe. After having mulled this over for a few days and typing this out, I=20 realize that the "pipe" is really just a fifo and that in this case the=20 fifo is a named pipe on the file system. I could do the same thing with = a file. Historically I would have done the same thing with a file. But = now I realize that the file is not required and that I can use a fifo=20 which is in memory and never hits the disk. (Save for creating the name = interface to the pipe / fifo.) At least, I think that's all accurate. I would be very eager to learn from anyone who is willing to teach me=20 pointers. :-) --=20 Grant. . . . unix || die --------------ms080302010505000402070804 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCC CzkwggUhMIIECaADAgECAhA53zcXtFD9dENby64EqrKqMA0GCSqGSIb3DQEBCwUAMIGWMQsw CQYDVQQGEwJHQjEbMBkGA1UECBMSR3JlYXRlciBNYW5jaGVzdGVyMRAwDgYDVQQHEwdTYWxm b3JkMRgwFgYDVQQKEw9TZWN0aWdvIExpbWl0ZWQxPjA8BgNVBAMTNVNlY3RpZ28gUlNBIENs aWVudCBBdXRoZW50aWNhdGlvbiBhbmQgU2VjdXJlIEVtYWlsIENBMB4XDTE5MTExOTAwMDAw MFoXDTIwMTExODIzNTk1OVowKzEpMCcGCSqGSIb3DQEJARYaZ3RheWxvckB0bmV0Y29uc3Vs dGluZy5uZXQwggEiMA0GCSqGSIb3DQEBAQUAA4IBDwAwggEKAoIBAQCwIZcEJcuE7mUfxJnD I8oOSX/TvAhoP11agD++8L7Ok8fFJhJK0lOVRsq1M6lF2E2Vzuyffg2ppbecWvHcIRadsaiG 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