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Diffstat (limited to 'print.html')
| -rw-r--r-- | print.html | 85 |
1 files changed, 81 insertions, 4 deletions
@@ -377,7 +377,7 @@ builtin <code>RS</code> variable.</li> but can be changed via the builtin variable <code>FS</code> or command line option <code>-F</code>.</li> </ol> -<p>Field are accessed as follows:</p> +<p>Fields are accessed as follows:</p> <ul> <li><code>$0</code> whole <code>record</code></li> <li><code>$1</code> field one</li> @@ -399,6 +399,83 @@ 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> <h1><a class="header" href="#gdb1" id="gdb1">gdb(1)</a></h1> <h1><a class="header" href="#cli" id="cli">CLI</a></h1> <pre><code class="language-markdown"> gdb [opts] [prg [-c coredump | -p pid]] @@ -492,7 +569,7 @@ fields ----> run associated action # cmds end </code></pre> -<h1><a class="header" href="#examples" id="examples">Examples</a></h1> +<h1><a class="header" href="#examples-1" id="examples-1">Examples</a></h1> <h2><a class="header" href="#catch-sigsegv-and-execute-commands" id="catch-sigsegv-and-execute-commands">Catch SIGSEGV and execute commands</a></h2> <p>This creates a <code>catchpoint</code> for the <code>SIGSEGV</code> signal and attached the <code>command</code> to it.</p> @@ -634,7 +711,7 @@ executed. To workaround that bug one can create a wrapper function which calls trace=signal ............... trace signal related syscalls signal ..................... trace signals delivered to the process </code></pre> -<h1><a class="header" href="#examples-1" id="examples-1">Examples</a></h1> +<h1><a class="header" href="#examples-2" id="examples-2">Examples</a></h1> <p>Trace <code>open(2)</code> & <code>socket(2)</code> syscalls for a running process + child processes:</p> <pre><code class="language-markdown">strace -f -e trace=open,socket -p <pid> </code></pre> @@ -656,7 +733,7 @@ executed. To workaround that bug one can create a wrapper function which calls AP ......... append TR ......... truncate </code></pre> -<h1><a class="header" href="#examples-2" id="examples-2">Examples</a></h1> +<h1><a class="header" href="#examples-3" id="examples-3">Examples</a></h1> <h2><a class="header" href="#file-flags" id="file-flags">File flags</a></h2> <p>Show open files with file flags for process:</p> <pre><code class="language-markdown">lsof +fg -p <pid> |