From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-1.1 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 14116 invoked from network); 3 Mar 2023 19:06:34 -0000 Received: from minnie.tuhs.org (2600:3c01:e000:146::1) by inbox.vuxu.org with ESMTPUTF8; 3 Mar 2023 19:06:34 -0000 Received: from minnie.tuhs.org (localhost [IPv6:::1]) by minnie.tuhs.org (Postfix) with ESMTP id 9E7C7432A1; Sat, 4 Mar 2023 05:06:32 +1000 (AEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=tuhs.org; s=dkim; t=1677870392; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:mime-version:mime-version: content-type:content-type:in-reply-to:in-reply-to: references:references:list-id:list-help:list-owner:list-unsubscribe: list-subscribe:list-post; bh=Y/vehzp3SOLeVhh9N1tdTVXSftU2EYQ8ybgG+oM4hWo=; b=XW/Mef6ooxHacNq3WEGUKa/RPyWsOC0sHev4fCtMfmGTo4vpgnJlcoAOlopO++3HeahCJj 6ZpbsJl9AP4kyJwmUc6zEASuEwHQ5cuB45SdovaIdIHy8srmvh8rx8AF6Qdafg/Q1cc6oz 1xbugn0rNDd0iKmf4He8031pQ1k31vA= Received: from tncsrv06.tnetconsulting.net (tncsrv06.tnetconsulting.net [IPv6:2600:3c00:e000:1e9::8849]) by minnie.tuhs.org (Postfix) with ESMTPS id E6A8C4329F for ; Sat, 4 Mar 2023 05:06:24 +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 323J6NUH002120 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NO) for ; Fri, 3 Mar 2023 13:06:24 -0600 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=tnetconsulting.net; s=2019; t=1677870384; bh=Y/vehzp3SOLeVhh9N1tdTVXSftU2EYQ8ybgG+oM4hWo=; 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=5X9EswO5vP1LZFGvVueIU7w6U4WljBbyKgT/1TFNs7if1oyurpdvFLIjdKbJR6gCT z/SxkU/Mln0zWuECOagT+UOBD6QKZ0QON0N2ilyC6O8Zzw7TeuXA7K0GYNuIu2MTvm z+DWPuw4laWRj57QMVWrv05gtLclfNmAnBzAaXC0= To: coff@tuhs.org References: <8d1de5c8-1f34-3d37-395d-0f1da7b062ec@spamtrap.tnetconsulting.net> Organization: TNet Consulting Message-ID: Date: Fri, 3 Mar 2023 12:06:17 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <8d1de5c8-1f34-3d37-395d-0f1da7b062ec@spamtrap.tnetconsulting.net> Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-256; boundary="------------ms010605070703010504000001" Message-ID-Hash: JBNTD2NDJRMQW4QJOFAKJ3QQK4WAWAJD X-Message-ID-Hash: JBNTD2NDJRMQW4QJOFAKJ3QQK4WAWAJD X-MailFrom: gtaylor@tnetconsulting.net X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header X-Mailman-Version: 3.3.6b1 Precedence: list Subject: [COFF] Re: Requesting thoughts on extended regular expressions in grep. List-Id: Computer Old Farts Forum Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: From: Grant Taylor via COFF Reply-To: Grant Taylor This is a cryptographically signed message in MIME format. --------------ms010605070703010504000001 Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: quoted-printable Thank you all for very interesting and engaging comments & threads to=20 chase / pull / untangle. I'd like to expand / refine my original question a little bit. On 3/2/23 11:54 AM, Grant Taylor via COFF wrote: > I'd like some thoughts ~> input on extended regular expressions used=20 > with grep, specifically GNU grep -e / egrep. While some reading of the references that Clem provided I came across=20 multiple indications that back-references can be problematic from a=20 performance stand point. So I'd like to know if all back-references are problematic, or if very=20 specific back-references are okay. Suppose I have the following two lines: aaa aaa aaa bbb Does the following RE w/ back-reference introduce a big performance penal= ty? (aaa|bbb) \1 As in: % echo "aaa aaa" | egrep "(aaa|bbb) \1" aaa aaa I can easily see how a back reference to something that is not a fixed=20 length can become a rabbit hole. But I'm wondering if a back-reference=20 to -- what I think is called -- an alternation (with length fixed in the = RE) is a performance hit or not. Now to read and reply to the many good comments that people have shared. = :-) --=20 Grant. . . . unix || die --------------ms010605070703010504000001 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 CzowggUiMIIECqADAgECAhEAw8IZWQHDVuWWKHZeojBgoDANBgkqhkiG9w0BAQsFADCBljEL MAkGA1UEBhMCR0IxGzAZBgNVBAgTEkdyZWF0ZXIgTWFuY2hlc3RlcjEQMA4GA1UEBxMHU2Fs Zm9yZDEYMBYGA1UEChMPU2VjdGlnbyBMaW1pdGVkMT4wPAYDVQQDEzVTZWN0aWdvIFJTQSBD bGllbnQgQXV0aGVudGljYXRpb24gYW5kIFNlY3VyZSBFbWFpbCBDQTAeFw0yMjExMTQwMDAw MDBaFw0yMzExMTQyMzU5NTlaMCsxKTAnBgkqhkiG9w0BCQEWGmd0YXlsb3JAdG5ldGNvbnN1 bHRpbmcubmV0MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAzOnBjTJUlBTzN81c PlYErJc9kEbTI/hXq0NA6ZoG4VM6puYTEXtITANjgX+NRwwHjldESnC8dvh6Mx5ckEk9sWoD 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