From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=5.0 tests=MAILING_LIST_MULTI, RCVD_IN_DNSWL_NONE autolearn=ham autolearn_force=no version=3.4.2 Received: from primenet.com.au (ns1.primenet.com.au [203.24.36.2]) by inbox.vuxu.org (OpenSMTPD) with ESMTP id d2e4466a for ; Fri, 28 Jun 2019 11:05:20 +0000 (UTC) Received: (qmail 15062 invoked by alias); 28 Jun 2019 11:05:10 -0000 Mailing-List: contact zsh-users-help@zsh.org; run by ezmlm Precedence: bulk X-No-Archive: yes List-Id: Zsh Users List List-Post: List-Help: List-Unsubscribe: X-Seq: 23991 Received: (qmail 10776 invoked by uid 1010); 28 Jun 2019 11:05:10 -0000 X-Qmail-Scanner-Diagnostics: from joooj.vinc17.net by f.primenet.com.au (envelope-from , uid 7791) with qmail-scanner-2.11 (clamdscan: 0.101.2/25489. spamassassin: 3.4.2. Clear:RC:0(155.133.131.76):SA:0(-1.9/5.0):. Processed in 1.374135 secs); 28 Jun 2019 11:05:10 -0000 X-Envelope-From: vincent@vinc17.net X-Qmail-Scanner-Mime-Attachments: | X-Qmail-Scanner-Zip-Files: | Received-SPF: none (ns1.primenet.com.au: domain at vinc17.net does not designate permitted sender hosts) Date: Fri, 28 Jun 2019 13:04:30 +0200 From: Vincent Lefevre To: zsh-users@zsh.org Subject: kill the LHS command of a pipe once the RHS command terminates Message-ID: <20190628110430.GA13790@zira.vinc17.org> Mail-Followup-To: zsh-users@zsh.org MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit X-Mailer-Info: https://www.vinc17.net/mutt/ User-Agent: Mutt/1.12.1+33 (6a74e24e) vl-117499 (2019-06-23) With some commands I pipe the output to a pager, and when quitting the pager, I want the command to terminate immediately (so that it doesn't consume more resources) and want the shell prompt back. Here are examples with "head -n 1" instead of a pager. * With just a pipe: zira% { echo foo; sleep 3; echo err >&2 } | head -n 1 foo [wait for 3 seconds] err zira% The issue is that when "head -n 1" terminates (just after "echo foo"), the left-hand-side command is still running. Thus it still consumes resources, and I also have to wait for the shell prompt, which is bad. * With a process substitution: zira% head -n 1 <(echo foo; sleep 3; echo err >&2) foo zira% Here I get the shell prompt back immediately, which is good. But the left-hand-side command is still running, so that it still consumes resources; moreover, after the 3 seconds, I get zira% err In practice, one may want to redirect stderr to the pager too (not always, though); this avoids this second issue, but not the first one, which is that the left-hand-side command still consumes resources. Does zsh provide a feature to kill the left-hand-side command in a clean way (without a race condition, without a temporary file...)? -- Vincent Lefèvre - Web: 100% accessible validated (X)HTML - Blog: Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)