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(Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar"> - <i class="fa fa-search"></i> - </button> - - </div> - - <h1 class="menu-title">Notes</h1> - - <div class="right-buttons"> - <a href="../print.html" title="Print this book" aria-label="Print this book"> - <i id="print-button" class="fa fa-print"></i> - </a> - - </div> - </div> - </div> - - - <div id="search-wrapper" class="hidden"> - <form id="searchbar-outer" class="searchbar-outer"> - <input type="search" name="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header"> - </form> - <div id="searchresults-outer" class="searchresults-outer hidden"> - <div id="searchresults-header" class="searchresults-header"></div> - <ul id="searchresults"> - </ul> - </div> - </div> - - - <!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM --> - <script type="text/javascript"> - document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible'); - document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible'); - Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) { - link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1); - }); - </script> - - <div id="content" class="content"> - <main> - <h1><a class="header" href="#awk1" id="awk1">awk(1)</a></h1> -<pre><code class="language-markdown">awk [opt] program [input] - -F <sepstr> field separator string (can be regex) - program awk program - input file or stdin if not file given -</code></pre> -<h2><a class="header" href="#input-processing" id="input-processing">Input processing</a></h2> -<p>Input is processed in two stages:</p> -<ol> -<li>Splitting input into a sequence of <code>records</code>. -By default split at <code>newline</code> character, but can be changed via the -builtin <code>RS</code> variable.</li> -<li>Splitting a <code>record</code> into <code>fields</code>. By default strings without <code>whitespace</code>, -but can be changed via the builtin variable <code>FS</code> or command line option -<code>-F</code>.</li> -</ol> -<p>Fields are accessed as follows:</p> -<ul> -<li><code>$0</code> whole <code>record</code></li> -<li><code>$1</code> field one</li> -<li><code>$2</code> field two</li> -<li>...</li> -</ul> -<h2><a class="header" href="#program" id="program">Program</a></h2> -<p>An <code>awk</code> program is composed of pairs of the form:</p> -<pre><code class="language-markdown">pattern { action } -</code></pre> -<p>The program is run against each <code>record</code> in the input stream. If a <code>pattern</code> -matches a <code>record</code> the corresponding <code>action</code> is executed and can access the -<code>fields</code>.</p> -<pre><code class="language-markdown">INPUT - | - v -record ----> ∀ pattern matched - | | - v v -fields ----> run associated action -</code></pre> -<p>Any valid awk <code>expr</code> can be a <code>pattern</code>.</p> -<h3><a class="header" href="#special-pattern" id="special-pattern">Special pattern</a></h3> -<p>awk provides two special patterns, <code>BEGIN</code> and <code>END</code>, which can be used -multiple times. Actions with those patterns are <strong>executed exactly once</strong>.</p> -<ul> -<li><code>BEGIN</code> actions are run before processing the first record</li> -<li><code>END</code> actions are run after processing the last record</li> -</ul> -<h3><a class="header" href="#special-variables" id="special-variables">Special variables</a></h3> -<ul> -<li><code>RS</code> <em>record separator</em>: first char is the record separator, by default -<newline></li> -<li><code>FS</code> <em>field separator</em>: regex to split records into fields, by default -<space></li> -<li><code>NR</code> <em>number record</em>: number of current record</li> -</ul> -<h3><a class="header" href="#special-statements--functions" id="special-statements--functions">Special statements & functions</a></h3> -<ul> -<li> -<p><code>printf "fmt", args...</code></p> -<p>Print format string, args are comma separated.</p> -<ul> -<li><code>%s</code> string</li> -<li><code>%d</code> decimal</li> -<li><code>%x</code> hex</li> -<li><code>%f</code> float</li> -</ul> -<p>Width can be specified as <code>%Ns</code>, this reserves <code>N</code> chars for a string. -For floats one can use <code>%N.Mf</code>, <code>N</code> is the total number including <code>.</code> and -<code>M</code>.</p> -</li> -<li> -<p><code>strftime("fmt")</code></p> -<p>Print time stamp formatted by <code>fmt</code>.</p> -<ul> -<li><code>%Y</code> full year (eg 2020)</li> -<li><code>%m</code> month (01-12)</li> -<li><code>%d</code> day (01-31)</li> -<li><code>%F</code> alias for <code>%Y-%m-%d</code></li> -<li><code>%H</code> hour (00-23)</li> -<li><code>%M</code> minute (00-59)</li> -<li><code>%S</code> second (00-59)</li> -<li><code>%T</code> alias for <code>%H:%M:%S</code></li> -</ul> -</li> -</ul> -<h2><a class="header" href="#examples" id="examples">Examples</a></h2> -<h3><a class="header" href="#filter-records" id="filter-records">Filter records</a></h3> -<pre><code class="language-bash">awk 'NR%2 == 0 { print $0 }' <file> -</code></pre> -<p>The pattern <code>NR%2 == 0</code> matches every second record and the action <code>{ print $0 }</code> -prints the whole record.</p> -<h3><a class="header" href="#capture-in-variables" id="capture-in-variables">Capture in variables</a></h3> -<pre><code class="language-bash"># /proc/<pid>/status -# Name: cat -# ... -# VmRSS: 516 kB -# ... - -for f in /proc/*/status; do - cat $f | awk ' - /^VmRSS/ { rss = $2/1024 } - /^Name/ { name = $2 } - END { printf "%16s %6d MB\n", name, rss }'; -done | sort -k2 -n -</code></pre> -<p>We capture values from <code>VmRSS</code> and <code>Name</code> into variables and print them at the -<code>END</code> once processing all records is done.</p> -<h3><a class="header" href="#run-shell-command-and-capture-output" id="run-shell-command-and-capture-output">Run shell command and capture output</a></h3> -<pre><code class="language-bash">cat /proc/1/status | awk ' - /^Pid/ { - "ps --no-header -o user " $2 | getline user; - print user - }' -</code></pre> -<p>We build a <code>ps</code> command line and capture the first line of the processes output -in the <code>user</code> variable and then print it.</p> - - </main> - - <nav class="nav-wrapper" aria-label="Page navigation"> - <!-- Mobile navigation buttons --> - - <a rel="prev" href="../misc/git.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left"> - <i class="fa fa-angle-left"></i> - </a> - - - - <a rel="next" href="../misc/emacs.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> - <i class="fa fa-angle-right"></i> - </a> - - - <div style="clear: both"></div> - </nav> - </div> - </div> - - <nav class="nav-wide-wrapper" aria-label="Page navigation"> - - <a href="../misc/git.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left"> - <i class="fa fa-angle-left"></i> - </a> - - - - <a href="../misc/emacs.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> - <i class="fa fa-angle-right"></i> - </a> - - </nav> - - </div> - - - - - - - - - <script type="text/javascript"> - window.playpen_copyable = true; - </script> - - - - - - <script src="../elasticlunr.min.js" type="text/javascript" charset="utf-8"></script> - <script src="../mark.min.js" type="text/javascript" charset="utf-8"></script> - <script src="../searcher.js" type="text/javascript" charset="utf-8"></script> - - - <script src="../clipboard.min.js" type="text/javascript" charset="utf-8"></script> - <script src="../highlight.js" type="text/javascript" charset="utf-8"></script> - <script src="../book.js" type="text/javascript" charset="utf-8"></script> - - <!-- Custom JS scripts --> - - - - - </body> -</html> |