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+<?xml version="1.0" encoding="utf-8"?>
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+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
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+"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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+<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
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+<head>
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+<!-- 2022-11-12 Sat 04:46 -->
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+<meta http-equiv="Content-Type" content="text/html;charset=utf-8" />
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+<meta name="viewport" content="width=device-width, initial-scale=1" />
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+<title>Grep Patterns … things I never knew.</title>
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+<meta name="author" content="George M Jones" />
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+<meta name="generator" content="Org Mode" />
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+<style>
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+ #content { max-width: 60em; margin: auto; }
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+ .title { text-align: center;
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+ margin-bottom: .2em; }
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+ font-size: medium;
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+ font-weight: bold;
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+ margin-top:0; }
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+ .todo { font-family: monospace; color: red; }
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+ padding: 2px; font-size: 80%; font-weight: normal; }
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+ .org-center { margin-left: auto; margin-right: auto; text-align: center; }
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+ .underline { text-decoration: underline; }
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+ #postamble p, #preamble p { font-size: 90%; margin: .2em; }
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+ p.verse { margin-left: 3%; }
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+ pre {
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+ padding: 8pt;
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+ font-family: monospace;
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+ overflow: auto;
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+ margin: 1.2em;
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+ }
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+ pre.src {
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+ }
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+ color: #555;
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+ background-color: #f2f2f299;
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+ }
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+ pre.src:hover:before { display: inline; margin-top: 14px;}
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+ /* Languages per Org manual */
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+ /* pre.src-C++ doesn't work in CSS */
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+ pre.src-clojure:before { content: 'Clojure'; }
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+ pre.src-ebnf2ps:before { content: 'ebfn2ps'; }
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+ /* additional language identifiers per "defun org-babel-execute"
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+ in ob-*.el */
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+ pre.src-cpp:before { content: 'C++'; }
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+ pre.src-abc:before { content: 'ABC'; }
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+ pre.src-coq:before { content: 'Coq'; }
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+ pre.src-groovy:before { content: 'Groovy'; }
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+ /* additional language identifiers from org-babel-shell-names in
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+ ob-shell.el: ob-shell is the only babel language using a lambda to put
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+ the execution function name together. */
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+ pre.src-bash:before { content: 'bash'; }
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+ pre.src-mksh:before { content: 'mksh'; }
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+ pre.src-posh:before { content: 'posh'; }
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+ /* Additional Emacs modes also supported by the LaTeX listings package */
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+ pre.src-ada:before { content: 'Ada'; }
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+ pre.src-asm:before { content: 'Assembler'; }
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+ pre.src-caml:before { content: 'Caml'; }
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+ pre.src-delphi:before { content: 'Delphi'; }
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+ pre.src-html:before { content: 'HTML'; }
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+ pre.src-idl:before { content: 'IDL'; }
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+ pre.src-mercury:before { content: 'Mercury'; }
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+ pre.src-metapost:before { content: 'MetaPost'; }
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+ pre.src-tcl:before { content: 'tcl'; }
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+ pre.src-tex:before { content: 'TeX'; }
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+ pre.src-plain-tex:before { content: 'Plain TeX'; }
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+ pre.src-verilog:before { content: 'Verilog'; }
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+ pre.src-vhdl:before { content: 'VHDL'; }
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+ pre.src-xml:before { content: 'XML'; }
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+ pre.src-nxml:before { content: 'XML'; }
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+ /* add a generic configuration mode; LaTeX export needs an additional
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+ (add-to-list 'org-latex-listings-langs '(conf " ")) in .emacs */
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+ pre.src-conf:before { content: 'Configuration File'; }
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+
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+ table { border-collapse:collapse; }
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+ caption.t-above { caption-side: top; }
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+ caption.t-bottom { caption-side: bottom; }
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+ td.org-right { text-align: right; }
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+ td.org-left { text-align: left; }
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+ td.org-center { text-align: center; }
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+ dt { font-weight: bold; }
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+ .footpara { display: inline; }
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+ .footdef { margin-bottom: 1em; }
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+ .figure { padding: 1em; }
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+ .figure p { text-align: center; }
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+ .equation-container {
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+ display: table;
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+ text-align: center;
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+ width: 100%;
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+ }
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+ .equation {
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+ vertical-align: middle;
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+ }
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+ .equation-label {
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+ display: table-cell;
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+ text-align: right;
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+ vertical-align: middle;
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+ }
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+ .inlinetask {
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+ padding: 10px;
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+ border: 2px solid gray;
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+ margin: 10px;
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+ background: #ffffcc;
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+ }
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+ #org-div-home-and-up
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+ { text-align: right; font-size: 70%; white-space: nowrap; }
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+ textarea { overflow-x: auto; }
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+ .linenr { font-size: smaller }
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+ .code-highlighted { background-color: #ffff00; }
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+ .org-info-js_info-navigation { border-style: none; }
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+ #org-info-js_console-label
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+ { font-size: 10px; font-weight: bold; white-space: nowrap; }
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+ .org-info-js_search-highlight
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+ { background-color: #ffff00; color: #000000; font-weight: bold; }
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+ .org-svg { }
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+</style>
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+</head>
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+<body>
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+<div id="preamble" class="status">
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+<h1 class="title">Grep Patterns … things I never knew.</h1>
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+ <p class="subtitle"></p>
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+ <br>
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+ <p class="subtitle">George M Jones</p>
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+ <p class="subtitle"><a href="mailto:gmj@pobox.com">gmj@pobox.com</a></p>
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+ <p class="subtitle"></p>
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+</div>
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+<div id="content" class="content">
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+<h1 class="title">Grep Patterns … things I never knew.</h1>
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+<p>
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+This was an exercise to understand GNU grep regular expressions and
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+options.
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+</p>
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+
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+<p>
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+<a href="https://man7.org/linux/man-pages/man1/grep.1.html">https://man7.org/linux/man-pages/man1/grep.1.html</a>
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+</p>
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+
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+<pre class="example" id="org94cd5ca">
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+
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+#
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+# The normal use cases
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+#
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+
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+# A file to grep
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+$ cat foo.txt
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+foo
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+foo foo
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+foo bar
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+foo bar baz
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+foo|bar|ba
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+
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+# basic regexs (-G) by default. '|' NOT special.
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+$ grep 'bar|baz' foo.txt
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+foo|bar|baz
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+
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+# same
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+$ grep -e 'bar|baz' foo.txt
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+foo|bar|baz
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+
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+# basic regexps. '\' to make '|' "special"
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+$ grep 'bar\|baz' foo.txt
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+foo bar
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+foo bar baz
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+foo|bar|baz
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+
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+# extended expressions. '|' IS special.
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+$ grep -E 'bar|baz' foo.txt
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+foo bar
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+foo bar baz
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+foo|bar|baz
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+
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+#
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+# The suprizing truth about "-e|--regexp"
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+#
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+
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+# -e (and --regex ) specify PATTERNs, NOT regexps
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+#
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+# "-e 'bar|baz'" specifies 'bar|baz' as a PATTERN NOT a regexp.
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+#
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+# The (non-)interpretation of patterns as regexps
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+# comes from the use of -G (default), -E, -F or -P
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+#
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+# In this example it is a basic regex because -G is implied.
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+#
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+$ grep -e 'bar|baz' foo.txt
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+foo|bar|baz
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+
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+
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+#
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+# newlines to separate patterns. Who knew?
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+#
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+
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+# per the man page:
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+# NAME
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+# grep - print lines that match patterns
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+#
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+# SYNOPSIS
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+# grep [OPTION...] PATTERNS [FILE...]
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+#
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+# DESCRIPTION
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+# grep searches for PATTERNS in each FILE. PATTERNS is one or more
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+# patterns separated by newline characters,
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+# ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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+#
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+
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+$ grep `printf 'bar\nbaz'` foo.txt
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+foo.txt:foo bar
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+foo.txt:foo bar baz
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+foo.txt:foo|bar|baz
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+</pre>
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+</div>
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+</body>
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+</html>
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