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Diffstat (limited to 'posts/6/index.html')
| -rw-r--r-- | posts/6/index.html | 18 |
1 files changed, 9 insertions, 9 deletions
diff --git a/posts/6/index.html b/posts/6/index.html index 2828d15..4baa0c6 100644 --- a/posts/6/index.html +++ b/posts/6/index.html @@ -149,7 +149,7 @@ Redirection File Redirection 0 is standard input, 1 is standard output, 2 is sta <p>the connection to the stream used by FD <code>y</code> is copied to FD <code>x</code></p> <p><code>curl cip.cc > result 2>&1</code></p> <p><code>ping localhost > result 2>&1</code></p> -<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:2;-o-tab-size:2;tab-size:2;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="font-style:italic"># exec can be used to change the file descriptors of bash itself,</span> +<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="font-style:italic"># exec can be used to change the file descriptors of bash itself,</span> </span></span><span style="display:flex;"><span><span style="font-style:italic"># and if you use an x that doesn't yet exist,</span> </span></span><span style="display:flex;"><span><span style="font-style:italic"># bash will create a new file descriptor ("plug") for you with that number.</span> </span></span><span style="display:flex;"><span><span style="font-style:italic"># - in command is to close new FD 3 we'd created before.</span> @@ -172,13 +172,13 @@ Redirection File Redirection 0 is standard input, 1 is standard output, 2 is sta <p><code>ping localhost &>result</code></p> </blockquote> <h3 id="here-documents">Here documents</h3> -<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:2;-o-tab-size:2;tab-size:2;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="font-style:italic"><<delimiter +<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="font-style:italic"><<delimiter </span></span></span><span style="display:flex;"><span><span style="font-style:italic"> Here document </span></span></span><span style="display:flex;"><span><span style="font-style:italic">delimiter</span> </span></span></code></pre></div><p>Make FD 0 read from the string between <code>delimiter</code>s</p> <blockquote> <p>Here-Documents are great for reading blocks of text to command line.</p> -<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:2;-o-tab-size:2;tab-size:2;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>cat <span style="font-style:italic"><< EOF +<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>cat <span style="font-style:italic"><< EOF </span></span></span><span style="display:flex;"><span><span style="font-style:italic">this is within here document </span></span></span><span style="display:flex;"><span><span style="font-style:italic">I can write as many lines as I like </span></span></span><span style="display:flex;"><span><span style="font-style:italic">and terminate with line of demiliter only @@ -189,7 +189,7 @@ Redirection File Redirection 0 is standard input, 1 is standard output, 2 is sta <p>Make FD 0 read from the <code>string</code></p> <blockquote> <p>Here strings are very similar to here documents but more concise. They are generally preferred over here documents.</p> -<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:2;-o-tab-size:2;tab-size:2;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>cat <<< <span style="font-style:italic">"This, +<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>cat <<< <span style="font-style:italic">"This, </span></span></span><span style="display:flex;"><span><span style="font-style:italic">is the here strings. tab will also be read."</span> </span></span></code></pre></div></blockquote> <h3 id="moving-file-decipher">Moving file decipher</h3> @@ -197,7 +197,7 @@ Redirection File Redirection 0 is standard input, 1 is standard output, 2 is sta <p>Replace FD <code>x</code> with FD <code>y</code> and close FD <code>y</code></p> <blockquote> <p>Easy way of <code>[x]>&y, y>&-</code></p> -<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:2;-o-tab-size:2;tab-size:2;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="font-style:italic"># 3>&1-: copy FD 1 to FD 3 and close FD 1.</span> +<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="font-style:italic"># 3>&1-: copy FD 1 to FD 3 and close FD 1.</span> </span></span><span style="display:flex;"><span><span style="font-style:italic"># >&3-: copy FD 3 to FD 1 and close FD 3.</span> </span></span><span style="display:flex;"><span>exec 3>&1- >mylog; echo moo; exec >&3- </span></span></code></pre></div></blockquote> @@ -206,7 +206,7 @@ Redirection File Redirection 0 is standard input, 1 is standard output, 2 is sta <p>Open FD <code>x</code> for both reading and writing to <code>file</code></p> <blockquote> <p>The file descriptor at x is opened with a stream to the file that can be used for writing as well as reading bytes. Usually you’ll use two file descriptors for this. <strong>One of the rare cases where this is useful is when setting up a stream with a read/write device such as a network socket</strong>.</p> -<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:2;-o-tab-size:2;tab-size:2;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>exec 5<>aFile +<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>exec 5<>aFile </span></span><span style="display:flex;"><span>cat >&5 <span style="font-style:italic">"Hello world"</span> <span style="font-style:italic"># make FD 1 write to where FD 5 currently writing, copy file descriptor FD 5 to FD 1</span> </span></span><span style="display:flex;"><span>cat <&5 <span style="font-style:italic"># make FD 0 read from where FD 5 currently reading, copy file descriptor FD 5 to FD 0, then cat will send content to FD 1</span> </span></span></code></pre></div></blockquote> @@ -248,7 +248,7 @@ zsh. : <code>setopt extendedglob</code> </ol> <h3 id="command-substitution">Command Substitution</h3> <p>we can expansion commands within commands, but must use double-quote <code>""</code> instead of <code>''</code></p> -<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:2;-o-tab-size:2;tab-size:2;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="font-style:italic"># this will output contents in hello.h to screen</span> +<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="font-style:italic"># this will output contents in hello.h to screen</span> </span></span><span style="display:flex;"><span>cat hello.h </span></span><span style="display:flex;"><span> </span></span><span style="display:flex;"><span><span style="font-style:italic"># this will expand `cat hello.h` to real contents in </span> @@ -296,7 +296,7 @@ zsh. : <code>setopt extendedglob</code> <p>In addition, we can put braces (<code>{</code> and <code>}</code>) around our parameter, which indicates where variable is about to begin and end.</p> <blockquote> <p>e.g. <code>name=orange; echo there are 4 "${name}s"</code> <code>there are 4 oranges</code>.</p> -<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:2;-o-tab-size:2;tab-size:2;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>name=orange +<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>name=orange </span></span><span style="display:flex;"><span>echo <span style="font-style:italic">"there are 4 </span><span style="font-weight:bold;font-style:italic">${</span>name<span style="font-weight:bold;font-style:italic">}</span><span style="font-style:italic">s."</span> <span style="font-style:italic"># there are 4 oranges.</span> </span></span><span style="display:flex;"><span>echo <span style="font-style:italic">"there are 4 </span>$names<span style="font-style:italic">."</span> <span style="font-style:italic"># there are 4 .</span> </span></span></code></pre></div><p>here, we put <code>{}</code>around<code>name</code>so that bash can be told that suffix <code>s</code> is not a part of variable. otherwise, it will treat <code>names</code> as parameter and looking for its value, which is none in our example.</p> @@ -305,7 +305,7 @@ zsh. : <code>setopt extendedglob</code> <blockquote> <p>While expanding a parameter, it is possible to apply an operator to the expanding value without alternate original value.</p> <p>I use these mostly</p> -<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:2;-o-tab-size:2;tab-size:2;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="font-style:italic"># remove string before pattern ${name#pattern} shortest ${name##pattern} longest</span> +<div class="highlight"><pre tabindex="0" style="background-color:#fff;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="font-style:italic"># remove string before pattern ${name#pattern} shortest ${name##pattern} longest</span> </span></span><span style="display:flex;"><span><span style="font-style:italic"># remove string after pattern ${name%pattern} longest ${name%%pattern} shortest</span> </span></span><span style="display:flex;"><span><span style="font-style:italic"># delete first matching pattern ${name/pattern}</span> </span></span><span style="display:flex;"><span><span style="font-style:italic"># delete all matching pattern ${name//pattern}</span> |