Path: csiph.com!xmission!news.snarked.org!news.linkpendium.com!news.linkpendium.com!panix!usenet.stanford.edu!not-for-mail From: Chet Ramey Newsgroups: gnu.bash.bug Subject: Re: 'while read' loop performance (redirection vs pipeline) Date: Wed, 10 Jun 2020 09:49:52 -0400 Organization: ITS, Case Western Reserve University Lines: 24 Approved: bug-bash@gnu.org Message-ID: References: <1591789732.21528.14.camel@aliquot.org> <75f7cd6a-4442-9659-deed-78812de1d2b9@case.edu> Reply-To: chet.ramey@case.edu NNTP-Posting-Host: lists.gnu.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Trace: usenet.stanford.edu 1591797006 23678 209.51.188.17 (10 Jun 2020 13:50:06 GMT) X-Complaints-To: action@cs.stanford.edu Cc: chet.ramey@case.edu To: "Terence O'Gorman" , bug-bash@gnu.org Envelope-to: bug-bash@gnu.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=case.edu; s=smtp-primary; t=1591796997; bh=OKx5onrFMxdKDMFj4bEL/RkyRDgfDVoLPBz5fcjgCQ4=; h=Reply-To:Cc:Subject:To:References:From:Message-ID:Date: MIME-Version:In-Reply-To:Content-Type:Content-Transfer-Encoding; 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envelope-from=chet.ramey@case.edu; helo=mpv1-2015.case.edu X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/10 09:49:55 X-ACL-Warn: Detected OS = Linux 2.4.x-2.6.x [generic] X-Spam_score_int: -39 X-Spam_score: -4.0 X-Spam_bar: ---- X-Spam_report: (-4.0 / 5.0 requ) BAYES_00=-1.9, DKIM_INVALID=0.1, DKIM_SIGNED=0.1, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: bug-bash@gnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Bug reports for the GNU Bourne Again SHell List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Mailman-Original-Message-ID: <75f7cd6a-4442-9659-deed-78812de1d2b9@case.edu> X-Mailman-Original-References: <1591789732.21528.14.camel@aliquot.org> Xref: csiph.com gnu.bash.bug:16379 On 6/10/20 7:48 AM, Terence O'Gorman wrote: > Bash Version: 5.0 > Patch Level: 11 > Release Status: release > > > Description: > > The 'while read' loop exhibits very different performance depending on > whether input is via redirection or pipeline (and increasingly diverging > performance with any increased data). Here are some results from my > machine (also observed in versions 3.0 and 4.0): Two forks and one exec are expensive, as are the single-byte reads through the pipe. The single-byte reads are required because the shell is not allowed to read ahead in this case, since the remaining input may be intended for another process. -- ``The lyf so short, the craft so long to lerne.'' - Chaucer ``Ars longa, vita brevis'' - Hippocrates Chet Ramey, UTech, CWRU chet@case.edu http://tiswww.cwru.edu/~chet/