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<section id="fish-for-bash-users">
<h1>Fish for bash users<a class="headerlink" href="#fish-for-bash-users" title="Link to this heading">¶</a></h1>
<p>This is to give you a quick overview if you come from bash (or to a lesser extent other shells like zsh or ksh) and want to know how fish differs. Fish is intentionally not POSIX-compatible and as such some of the things you are used to work differently.</p>
<p>Many things are similar - they both fundamentally expand commandlines to execute commands, have pipes, redirections, variables, globs, use command output in various ways. This document is there to quickly show you the differences.</p>
<section id="command-substitutions">
<span id="bash-command-substitutions"></span><h2>Command substitutions<a class="headerlink" href="#command-substitutions" title="Link to this heading">¶</a></h2>
<p>Fish spells command substitutions as <code class="docutils literal notranslate"><span class="pre">$(command)</span></code> or <code class="docutils literal notranslate"><span class="pre">(command)</span></code>, but not <code class="docutils literal notranslate"><span class="pre">`command`</span></code>.</p>
<p>In addition, it only splits them on newlines instead of $IFS. If you want to split on something else, use <a class="reference internal" href="cmds/string-split.html"><span class="doc">string split</span></a>, <a class="reference internal" href="cmds/string-split.html"><span class="doc">string split0</span></a> or <a class="reference internal" href="cmds/string-collect.html"><span class="doc">string collect</span></a>. If those are used as the last command in a command substitution the splits they create are carried over. So:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="nf">for</span><span class="w"> </span><span class="no">i</span><span class="w"> </span><span class="nf">in</span><span class="w"> </span><span class="o">(</span><span class="nf">find</span><span class="w"> </span><span class="no">.</span><span class="w"> </span><span class="no">-print0</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">string</span><span class="w"> </span><span class="no">split0</span><span class="o">)</span>
</pre></div>
</div>
<p>will correctly handle all possible filenames.</p>
</section>
<section id="variables">
<h2>Variables<a class="headerlink" href="#variables" title="Link to this heading">¶</a></h2>
<p>Fish sets and erases variables with <a class="reference internal" href="cmds/set.html"><span class="doc">set</span></a> instead of <code class="docutils literal notranslate"><span class="pre">VAR=VAL</span></code> and a variety of separate builtins like <code class="docutils literal notranslate"><span class="pre">declare</span></code> and <code class="docutils literal notranslate"><span class="pre">unset</span></code> and <code class="docutils literal notranslate"><span class="pre">export</span></code>. <code class="docutils literal notranslate"><span class="pre">set</span></code> takes options to determine the scope and exportedness of a variable:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="c"># Define $PAGER *g*lobal and e*x*ported,</span>
<span class="c"># so this is like ``export PAGER=less``</span>
<span class="nf">set</span><span class="w"> </span><span class="no">-gx</span><span class="w"> </span><span class="no">PAGER</span><span class="w"> </span><span class="no">less</span>
<span class="c"># Define $alocalvariable only locally,</span>
<span class="c"># like ``local alocalvariable=foo``</span>
<span class="nf">set</span><span class="w"> </span><span class="no">-l</span><span class="w"> </span><span class="no">alocalvariable</span><span class="w"> </span><span class="no">foo</span>
</pre></div>
</div>
<p>or to erase variables:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="nf">set</span><span class="w"> </span><span class="no">-e</span><span class="w"> </span><span class="no">PAGER</span>
</pre></div>
</div>
<p><code class="docutils literal notranslate"><span class="pre">VAR=VAL</span></code> statements are available as environment overrides:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="no">PAGER</span><span class="o">=</span><span class="no">cat</span><span class="w"> </span><span class="nf">git</span><span class="w"> </span><span class="no">log</span>
</pre></div>
</div>
<p>Fish does not perform word splitting. Once a variable has been set to a value, that value stays as it is, so double-quoting variable expansions isn’t the necessity it is in bash. <a class="footnote-reference brackets" href="#id2" id="id1" role="doc-noteref"><span class="fn-bracket">[</span>1<span class="fn-bracket">]</span></a></p>
<p>For instance, here’s bash</p>
<div class="highlight-sh notranslate"><div class="highlight"><pre><span></span>><span class="w"> </span><span class="nv">foo</span><span class="o">=</span><span class="s2">"bar baz"</span>
><span class="w"> </span><span class="nb">printf</span><span class="w"> </span><span class="s1">'"%s"\n'</span><span class="w"> </span><span class="nv">$foo</span>
<span class="c1"># will print two lines, because we didn't double-quote</span>
<span class="c1"># this is word splitting</span>
<span class="s2">"bar"</span>
<span class="s2">"baz"</span>
</pre></div>
</div>
<p>And here is fish:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="gp">> </span><span class="nf">set</span><span class="w"> </span><span class="no">foo</span><span class="w"> </span><span class="s2">"bar baz"</span>
<span class="gp">> </span><span class="nf">printf</span><span class="w"> </span><span class="s1">'"%s"\n'</span><span class="w"> </span><span class="o">$foo</span>
<span class="go"># foo was set as one element,</span>
<span class="go"># so it will be passed as one element, so this is one line</span>
<span class="go">"bar baz"</span>
</pre></div>
</div>
<p>All variables are “arrays” (we use the term “lists”), and expanding a variable expands to all its elements, with each element as its own argument (like bash’s <code class="docutils literal notranslate"><span class="pre">"${var[@]}"</span></code>:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="gp">> </span><span class="nf">set</span><span class="w"> </span><span class="no">var</span><span class="w"> </span><span class="s2">"foo bar"</span><span class="w"> </span><span class="no">banana</span>
<span class="gp">> </span><span class="nf">printf</span><span class="w"> </span><span class="no">%s</span><span class="se">\n</span><span class="w"> </span><span class="o">$var</span>
<span class="go">foo bar</span>
<span class="go">banana</span>
</pre></div>
</div>
<p>Specific elements of a list can be selected:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="nf">echo</span><span class="w"> </span><span class="o">$list[</span><span class="no">5..7</span><span class="o">]</span>
</pre></div>
</div>
<p>The arguments to <code class="docutils literal notranslate"><span class="pre">set</span></code> are ordinary, so you can also set a variable to the output of a command:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="c"># Set lines to all the lines in file, one element per line</span>
<span class="nf">set</span><span class="w"> </span><span class="no">lines</span><span class="w"> </span><span class="o">(</span><span class="nf">cat</span><span class="w"> </span><span class="no">file</span><span class="o">)</span>
</pre></div>
</div>
<p>or a mixture of literal values and output:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="gp">> </span><span class="nf">set</span><span class="w"> </span><span class="no">numbers</span><span class="w"> </span><span class="no">1</span><span class="w"> </span><span class="no">2</span><span class="w"> </span><span class="no">3</span><span class="w"> </span><span class="o">(</span><span class="nf">seq</span><span class="w"> </span><span class="no">5</span><span class="w"> </span><span class="no">8</span><span class="o">)</span><span class="w"> </span><span class="no">9</span>
<span class="gp">> </span><span class="nf">printf</span><span class="w"> </span><span class="s1">'%s\n'</span><span class="w"> </span><span class="o">$numbers</span>
<span class="go">1</span>
<span class="go">2</span>
<span class="go">3</span>
<span class="go">5</span>
<span class="go">6</span>
<span class="go">7</span>
<span class="go">8</span>
<span class="go">9</span>
</pre></div>
</div>
<p>A <code class="docutils literal notranslate"><span class="pre">=</span></code> is unnecessary and unhelpful with <code class="docutils literal notranslate"><span class="pre">set</span></code> - <code class="docutils literal notranslate"><span class="pre">set</span> <span class="pre">foo</span> <span class="pre">=</span> <span class="pre">bar</span></code> will set the variable “foo” to two values: “=” and “bar”. <code class="docutils literal notranslate"><span class="pre">set</span> <span class="pre">foo=bar</span></code> will print an error.</p>
<p>See <a class="reference internal" href="language.html#variables"><span class="std std-ref">Shell variables</span></a> for more.</p>
<aside class="footnote-list brackets">
<aside class="footnote brackets" id="id2" role="doc-footnote">
<span class="label"><span class="fn-bracket">[</span><a role="doc-backlink" href="#id1">1</a><span class="fn-bracket">]</span></span>
<p>zsh also does not perform word splitting by default (the SH_WORD_SPLIT option controls this)</p>
</aside>
</aside>
</section>
<section id="wildcards-globs">
<span id="bash-globs"></span><h2>Wildcards (globs)<a class="headerlink" href="#wildcards-globs" title="Link to this heading">¶</a></h2>
<p>Fish only supports the <code class="docutils literal notranslate"><span class="pre">*</span></code> and <code class="docutils literal notranslate"><span class="pre">**</span></code> glob (and the deprecated <code class="docutils literal notranslate"><span class="pre">?</span></code> glob) as syntax. If a glob doesn’t match it fails the command (like with bash’s <code class="docutils literal notranslate"><span class="pre">failglob</span></code>) unless the command is <code class="docutils literal notranslate"><span class="pre">for</span></code>, <code class="docutils literal notranslate"><span class="pre">set</span></code> or <code class="docutils literal notranslate"><span class="pre">count</span></code> or the glob is used with an environment override (<code class="docutils literal notranslate"><span class="pre">VAR=*</span> <span class="pre">command</span></code>), in which case it expands to nothing (like with bash’s <code class="docutils literal notranslate"><span class="pre">nullglob</span></code> option).</p>
<p>Globbing doesn’t happen on expanded variables, so:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="nf">set</span><span class="w"> </span><span class="no">foo</span><span class="w"> </span><span class="s2">"*"</span>
<span class="nf">echo</span><span class="w"> </span><span class="o">$foo</span>
</pre></div>
</div>
<p>will not match any files.</p>
<p>There are no options to control globbing so it always behaves like that.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">**</span></code> glob will match in subdirectories as well. In other shells this often needs to be turned on with an option, like <code class="docutils literal notranslate"><span class="pre">setopt</span> <span class="pre">globstar</span></code> in bash.</p>
<p>Unlike bash, fish will also follow symlinks, and will sort the results in a natural sort, with included numbers compared as numbers. That means it will sort e.g. music tracks correctly even if they have numbers like <code class="docutils literal notranslate"><span class="pre">1</span></code> instead of <code class="docutils literal notranslate"><span class="pre">01</span></code>.</p>
<p>See <a class="reference internal" href="language.html#expand-wildcard"><span class="std std-ref">Wildcards</span></a> for more.</p>
</section>
<section id="quoting">
<h2>Quoting<a class="headerlink" href="#quoting" title="Link to this heading">¶</a></h2>
<p>Fish has two quoting styles: <code class="docutils literal notranslate"><span class="pre">""</span></code> and <code class="docutils literal notranslate"><span class="pre">''</span></code>. Variables are expanded in double-quotes, nothing is expanded in single-quotes.</p>
<p>There is no <code class="docutils literal notranslate"><span class="pre">$''</span></code>, instead the sequences that would transform are transformed <em>when unquoted</em>:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="gp">> </span><span class="nf">echo</span><span class="w"> </span><span class="no">a</span><span class="se">\n</span><span class="no">b</span>
<span class="go">a</span>
<span class="go">b</span>
</pre></div>
</div>
<p>See <a class="reference internal" href="language.html#quotes"><span class="std std-ref">Quotes</span></a> for more.</p>
</section>
<section id="string-manipulation">
<h2>String manipulation<a class="headerlink" href="#string-manipulation" title="Link to this heading">¶</a></h2>
<p>Fish does not have <code class="docutils literal notranslate"><span class="pre">${foo%bar}</span></code>, <code class="docutils literal notranslate"><span class="pre">${foo#bar}</span></code> and <code class="docutils literal notranslate"><span class="pre">${foo/bar/baz}</span></code>. Instead string manipulation is done by the <a class="reference internal" href="cmds/string.html"><span class="doc">string</span></a> builtin.</p>
<p>For example, to replace “bar” with “baz”:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="gp">> </span><span class="nf">string</span><span class="w"> </span><span class="no">replace</span><span class="w"> </span><span class="no">bar</span><span class="w"> </span><span class="no">baz</span><span class="w"> </span><span class="s2">"bar luhrmann"</span>
<span class="go">baz luhrmann</span>
</pre></div>
</div>
<p>It can also split strings:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="gp">> </span><span class="nf">string</span><span class="w"> </span><span class="no">split</span><span class="w"> </span><span class="s2">","</span><span class="w"> </span><span class="s2">"foo,bar"</span>
<span class="go">foo</span>
<span class="go">bar</span>
</pre></div>
</div>
<p>Match regular expressions as a replacement for <code class="docutils literal notranslate"><span class="pre">grep</span></code>:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="gp">> </span><span class="nf">echo</span><span class="w"> </span><span class="no">bababa</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">string</span><span class="w"> </span><span class="no">match</span><span class="w"> </span><span class="no">-r</span><span class="w"> </span><span class="s1">'aba$'</span>
<span class="go">aba</span>
</pre></div>
</div>
<p>Pad strings to a given width, with arbitrary characters:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="gp">> </span><span class="nf">string</span><span class="w"> </span><span class="no">pad</span><span class="w"> </span><span class="no">-c</span><span class="w"> </span><span class="no">x</span><span class="w"> </span><span class="no">-w</span><span class="w"> </span><span class="no">20</span><span class="w"> </span><span class="s2">"foo"</span>
<span class="go">xxxxxxxxxxxxxxxxxfoo</span>
</pre></div>
</div>
<p>Make strings lower/uppercase:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="gp">> </span><span class="nf">string</span><span class="w"> </span><span class="no">lower</span><span class="w"> </span><span class="no">Foo</span>
<span class="go">foo</span>
<span class="gp">> </span><span class="nf">string</span><span class="w"> </span><span class="no">upper</span><span class="w"> </span><span class="no">Foo</span>
<span class="go">FOO</span>
</pre></div>
</div>
<p>repeat strings, trim strings, escape strings or print a string’s length or width (in terminal cells).</p>
</section>
<section id="special-variables">
<h2>Special variables<a class="headerlink" href="#special-variables" title="Link to this heading">¶</a></h2>
<p>Some bash variables and their closest fish equivalent:</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">$*</span></code>, <code class="docutils literal notranslate"><span class="pre">$@</span></code>, <code class="docutils literal notranslate"><span class="pre">$1</span></code> and so on: <code class="docutils literal notranslate"><span class="pre">$argv</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">$?</span></code>: <code class="docutils literal notranslate"><span class="pre">$status</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">$$</span></code>: <code class="docutils literal notranslate"><span class="pre">$fish_pid</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">$#</span></code>: No variable, instead use <code class="docutils literal notranslate"><span class="pre">count</span> <span class="pre">$argv</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">$!</span></code>: <code class="docutils literal notranslate"><span class="pre">$last_pid</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">$0</span></code>: <code class="docutils literal notranslate"><span class="pre">status</span> <span class="pre">filename</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">$-</span></code>: Mostly <code class="docutils literal notranslate"><span class="pre">status</span> <span class="pre">is-interactive</span></code> and <code class="docutils literal notranslate"><span class="pre">status</span> <span class="pre">is-login</span></code></p></li>
</ul>
</section>
<section id="process-substitution">
<h2>Process substitution<a class="headerlink" href="#process-substitution" title="Link to this heading">¶</a></h2>
<p>Instead of <code class="docutils literal notranslate"><span class="pre"><(command)</span></code> fish uses <code class="docutils literal notranslate"><span class="pre">(command</span> <span class="pre">|</span> <span class="pre">psub)</span></code>. There is no equivalent to <code class="docutils literal notranslate"><span class="pre">>(command)</span></code>.</p>
<p>Note that both of these are bashisms, and most things can easily be expressed without. E.g. instead of:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="nf">source</span><span class="w"> </span><span class="o">(</span><span class="nf">command</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">psub</span><span class="o">)</span>
</pre></div>
</div>
<p>Use:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="nf">command</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">source</span>
</pre></div>
</div>
<p>as fish’s <a class="reference internal" href="cmds/source.html"><span class="doc">source</span></a> can read from stdin.</p>
</section>
<section id="heredocs">
<h2>Heredocs<a class="headerlink" href="#heredocs" title="Link to this heading">¶</a></h2>
<p>Fish does not have <code class="docutils literal notranslate"><span class="pre"><<EOF</span></code> “heredocs”. Instead of</p>
<div class="highlight-sh notranslate"><div class="highlight"><pre><span></span>cat<span class="w"> </span><span class="s"><<EOF</span>
<span class="s">some string</span>
<span class="s">some more string</span>
<span class="s">EOF</span>
</pre></div>
</div>
<p>use:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="nf">printf</span><span class="w"> </span><span class="no">%s</span><span class="se">\n</span><span class="w"> </span><span class="s2">"some string"</span><span class="w"> </span><span class="s2">"some more string"</span>
</pre></div>
</div>
<p>or:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="nf">echo</span><span class="w"> </span><span class="s2">"some string</span>
<span class="s2">some more string"</span>
<span class="c"># or if you want the quotes on separate lines:</span>
<span class="nf">echo</span><span class="w"> </span><span class="s2">"</span><span class="se">\</span>
<span class="s2">some string</span>
<span class="s2">some more string</span><span class="se">\</span>
<span class="s2">"</span>
</pre></div>
</div>
<p>Quotes are followed across newlines.</p>
<p>What “heredocs” do is:</p>
<ol class="arabic simple">
<li><p>Read/interpret the string, with special rules, up to the terminator. <a class="footnote-reference brackets" href="#id4" id="id3" role="doc-noteref"><span class="fn-bracket">[</span>2<span class="fn-bracket">]</span></a></p></li>
<li><p>Write the resulting string to a temporary file.</p></li>
<li><p>Start the command the heredoc is attached to with that file as stdin.</p></li>
</ol>
<p>This means it is essentially the same as just reading from a pipe, so:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="nf">echo</span><span class="w"> </span><span class="s2">"foo"</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">cat</span>
</pre></div>
</div>
<p>is mostly the same as</p>
<div class="highlight-sh notranslate"><div class="highlight"><pre><span></span>cat<span class="w"> </span><span class="s"><<EOF</span>
<span class="s">foo</span>
<span class="s">EOF</span>
</pre></div>
</div>
<p>Like with heredocs, the command has to be prepared to read from stdin. Sometimes this requires special options to be used, often giving a filename of <code class="docutils literal notranslate"><span class="pre">-</span></code> turns it on.</p>
<p>For example:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="nf">echo</span><span class="w"> </span><span class="s2">"xterm</span>
<span class="s2">rxvt-unicode"</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">pacman</span><span class="w"> </span><span class="no">--remove</span><span class="w"> </span><span class="no">-</span>
<span class="c"># is the same as (the `-` makes pacman read arguments from stdin)</span>
<span class="nf">pacman</span><span class="w"> </span><span class="no">--remove</span><span class="w"> </span><span class="no">xterm</span><span class="w"> </span><span class="no">rxvt-unicode</span>
</pre></div>
</div>
<p>and could be written in other shells as</p>
<div class="highlight-sh notranslate"><div class="highlight"><pre><span></span><span class="c1"># This "-" is still necessary - the heredoc is *also* passed over stdin!</span>
pacman<span class="w"> </span>--remove<span class="w"> </span>-<span class="w"> </span><span class="s"><< EOF</span>
<span class="s">xterm</span>
<span class="s">rxvt-unicode</span>
<span class="s">EOF</span>
</pre></div>
</div>
<p>So heredocs really are minor syntactical sugar that introduces a lot of special rules, which is why fish doesn’t have them. Pipes are a core concept, and are simpler and compose nicer.</p>
<aside class="footnote-list brackets">
<aside class="footnote brackets" id="id4" role="doc-footnote">
<span class="label"><span class="fn-bracket">[</span><a role="doc-backlink" href="#id3">2</a><span class="fn-bracket">]</span></span>
<p>For example, the “EOF” is just a convention, the terminator can be an arbitrary string, something like “THISISTHEEND” also works. And using <code class="docutils literal notranslate"><span class="pre"><<-</span></code> trims leading <em>tab</em> characters (but not other whitespace), so you can indent the lines, but only with tabs. Substitutions (variables, commands) are done on the heredoc by default, but not if the terminator is quoted: <code class="docutils literal notranslate"><span class="pre">cat</span> <span class="pre"><<</span> <span class="pre">"EOF"</span></code>.</p>
</aside>
</aside>
</section>
<section id="test-test">
<h2>Test (<code class="docutils literal notranslate"><span class="pre">test</span></code>, <code class="docutils literal notranslate"><span class="pre">[</span></code>, <code class="docutils literal notranslate"><span class="pre">[[</span></code>)<a class="headerlink" href="#test-test" title="Link to this heading">¶</a></h2>
<p>Fish has a POSIX-compatible <code class="docutils literal notranslate"><span class="pre">test</span></code> or <code class="docutils literal notranslate"><span class="pre">[</span></code> builtin. There is no <code class="docutils literal notranslate"><span class="pre">[[</span></code> and <code class="docutils literal notranslate"><span class="pre">test</span></code> does not accept <code class="docutils literal notranslate"><span class="pre">==</span></code> as a synonym for <code class="docutils literal notranslate"><span class="pre">=</span></code>. It can compare floating point numbers, however.</p>
<p><code class="docutils literal notranslate"><span class="pre">set</span> <span class="pre">-q</span></code> can be used to determine if a variable exists or has a certain number of elements (<code class="docutils literal notranslate"><span class="pre">set</span> <span class="pre">-q</span> <span class="pre">foo[2]</span></code>).</p>
</section>
<section id="arithmetic-expansion">
<h2>Arithmetic Expansion<a class="headerlink" href="#arithmetic-expansion" title="Link to this heading">¶</a></h2>
<p>Fish does not have <code class="docutils literal notranslate"><span class="pre">$((i+1))</span></code> arithmetic expansion, computation is handled by <a class="reference internal" href="cmds/math.html"><span class="doc">math</span></a>:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="nf">math</span><span class="w"> </span><span class="o">$i</span><span class="w"> </span><span class="no">+</span><span class="w"> </span><span class="no">1</span>
</pre></div>
</div>
<p>Unlike bash’s arithmetic, it can handle floating point numbers:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="gp">> </span><span class="nf">math</span><span class="w"> </span><span class="no">5</span><span class="w"> </span><span class="no">/</span><span class="w"> </span><span class="no">2</span>
<span class="go">2.5</span>
</pre></div>
</div>
<p>And also has some functions, like for trigonometry:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="gp">> </span><span class="nf">math</span><span class="w"> </span><span class="no">cos</span><span class="w"> </span><span class="no">2</span><span class="w"> </span><span class="no">x</span><span class="w"> </span><span class="no">pi</span>
<span class="go">1</span>
</pre></div>
</div>
<p>You can pass arguments to <code class="docutils literal notranslate"><span class="pre">math</span></code> separately like above or in quotes. Because fish uses <code class="docutils literal notranslate"><span class="pre">()</span></code> parentheses for <a class="reference internal" href="#bash-command-substitutions"><span class="std std-ref">command substitutions</span></a>, quoting is needed if you want to use them in your expression:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="gp">> </span><span class="nf">math</span><span class="w"> </span><span class="s1">'(5 + 2) * 4'</span>
</pre></div>
</div>
<p>Both <code class="docutils literal notranslate"><span class="pre">*</span></code> and <code class="docutils literal notranslate"><span class="pre">x</span></code> are valid ways to spell multiplication, but <code class="docutils literal notranslate"><span class="pre">*</span></code> needs to be quoted because it looks like a <a class="reference internal" href="#bash-globs"><span class="std std-ref">glob</span></a>.</p>
</section>
<section id="prompts">
<h2>Prompts<a class="headerlink" href="#prompts" title="Link to this heading">¶</a></h2>
<p>Fish does not use the <code class="docutils literal notranslate"><span class="pre">$PS1</span></code>, <code class="docutils literal notranslate"><span class="pre">$PS2</span></code> and so on variables. Instead the prompt is the output of the <a class="reference internal" href="cmds/fish_prompt.html"><span class="doc">fish_prompt</span></a> function, plus the <a class="reference internal" href="cmds/fish_mode_prompt.html"><span class="doc">fish_mode_prompt</span></a> function if <a class="reference internal" href="interactive.html#vi-mode"><span class="std std-ref">vi mode</span></a> is enabled. The output of the <a class="reference internal" href="cmds/fish_right_prompt.html"><span class="doc">fish_right_prompt</span></a> function is used for the right-sided prompt.</p>
<p>As an example, here’s a relatively simple bash prompt:</p>
<div class="highlight-sh notranslate"><div class="highlight"><pre><span></span><span class="c1"># <$HOSTNAME> <$PWD in blue> <Prompt Sign in Yellow> <Rest in default light white></span>
<span class="nv">PS1</span><span class="o">=</span><span class="s1">'\h\[\e[1;34m\]\w\[\e[m\] \[\e[1;32m\]\$\[\e[m\] '</span>
</pre></div>
</div>
<p>and a rough fish equivalent:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="nf">function</span><span class="w"> </span><span class="no">fish_prompt</span>
<span class="w"> </span><span class="nf">set</span><span class="w"> </span><span class="no">-l</span><span class="w"> </span><span class="no">prompt_symbol</span><span class="w"> </span><span class="s1">'$'</span>
<span class="w"> </span><span class="nf">fish_is_root_user</span><span class="p">;</span><span class="w"> </span><span class="o">and</span><span class="w"> </span><span class="nf">set</span><span class="w"> </span><span class="no">prompt_symbol</span><span class="w"> </span><span class="s1">'#'</span>
<span class="w"> </span><span class="nf">echo</span><span class="w"> </span><span class="no">-s</span><span class="w"> </span><span class="o">(</span><span class="nf">prompt_hostname</span><span class="o">)</span><span class="nv"> \</span>
<span class="nv"> </span><span class="o">(</span><span class="nf">set_color</span><span class="w"> </span><span class="no">blue</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="nf">prompt_pwd</span><span class="o">)</span><span class="nv"> \</span>
<span class="nv"> </span><span class="o">(</span><span class="nf">set_color</span><span class="w"> </span><span class="no">yellow</span><span class="o">)</span><span class="w"> </span><span class="o">$prompt_symbol</span><span class="w"> </span><span class="o">(</span><span class="nf">set_color</span><span class="w"> </span><span class="no">normal</span><span class="o">)</span>
<span class="nf">end</span>
</pre></div>
</div>
<p>This shows a few differences:</p>
<ul class="simple">
<li><p>Fish provides <a class="reference internal" href="cmds/set_color.html"><span class="doc">set_color</span></a> to color text. It can use the 16 named colors and also RGB sequences (so you could also use <code class="docutils literal notranslate"><span class="pre">set_color</span> <span class="pre">5555FF</span></code>)</p></li>
<li><p>Instead of introducing specific escapes like <code class="docutils literal notranslate"><span class="pre">\h</span></code> for the hostname, the prompt is a function. To achieve the effect of <code class="docutils literal notranslate"><span class="pre">\h</span></code>, fish provides helper functions like <a class="reference internal" href="cmds/prompt_hostname.html"><span class="doc">prompt_hostname</span></a>, which prints a shortened version of the hostname.</p></li>
<li><p>Fish offers other helper functions for adding things to the prompt, like <a class="reference internal" href="cmds/fish_vcs_prompt.html"><span class="doc">fish_vcs_prompt</span></a> for adding a display for common version control systems (git, mercurial, svn), and <a class="reference internal" href="cmds/prompt_pwd.html"><span class="doc">prompt_pwd</span></a> for showing a shortened <code class="docutils literal notranslate"><span class="pre">$PWD</span></code> (the user’s home directory becomes <code class="docutils literal notranslate"><span class="pre">~</span></code> and any path component is shortened).</p></li>
</ul>
<p>The default prompt is reasonably full-featured and its code can be read via <code class="docutils literal notranslate"><span class="pre">type</span> <span class="pre">fish_prompt</span></code>.</p>
<p>Fish does not have <code class="docutils literal notranslate"><span class="pre">$PS2</span></code> for continuation lines, instead it leaves the lines indented to show that the commandline isn’t complete yet.</p>
</section>
<section id="blocks-and-loops">
<h2>Blocks and loops<a class="headerlink" href="#blocks-and-loops" title="Link to this heading">¶</a></h2>
<p>Fish’s blocking constructs look a little different. They all start with a word, end in <code class="docutils literal notranslate"><span class="pre">end</span></code> and don’t have a second starting word:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="nf">for</span><span class="w"> </span><span class="no">i</span><span class="w"> </span><span class="nf">in</span><span class="w"> </span><span class="no">1</span><span class="w"> </span><span class="no">2</span><span class="w"> </span><span class="no">3</span><span class="p">;</span><span class="w"> </span><span class="nf">do</span>
<span class="w"> </span><span class="nf">echo</span><span class="w"> </span><span class="o">$i</span>
<span class="nf">done</span>
<span class="c"># becomes</span>
<span class="nf">for</span><span class="w"> </span><span class="no">i</span><span class="w"> </span><span class="nf">in</span><span class="w"> </span><span class="no">1</span><span class="w"> </span><span class="no">2</span><span class="w"> </span><span class="no">3</span>
<span class="w"> </span><span class="nf">echo</span><span class="w"> </span><span class="o">$i</span>
<span class="nf">end</span>
<span class="nf">while</span><span class="w"> </span><span class="nf">true</span><span class="p">;</span><span class="w"> </span><span class="nf">do</span>
<span class="w"> </span><span class="nf">echo</span><span class="w"> </span><span class="no">Weeee</span>
<span class="nf">done</span>
<span class="c"># becomes</span>
<span class="nf">while</span><span class="w"> </span><span class="nf">true</span>
<span class="w"> </span><span class="nf">echo</span><span class="w"> </span><span class="no">Weeeeeee</span>
<span class="nf">end</span>
<span class="nf">{</span>
<span class="w"> </span><span class="nf">echo</span><span class="w"> </span><span class="no">Hello</span>
<span class="nf">}</span>
<span class="c"># becomes</span>
<span class="nf">begin</span>
<span class="w"> </span><span class="nf">echo</span><span class="w"> </span><span class="no">Hello</span>
<span class="nf">end</span>
<span class="nf">if</span><span class="w"> </span><span class="nf">true</span><span class="p">;</span><span class="w"> </span><span class="nf">then</span>
<span class="w"> </span><span class="nf">echo</span><span class="w"> </span><span class="no">Yes</span><span class="w"> </span><span class="no">I</span><span class="w"> </span><span class="no">am</span><span class="w"> </span><span class="no">true</span>
<span class="nf">else</span>
<span class="w"> </span><span class="nf">echo</span><span class="w"> </span><span class="s2">"How is true not true?"</span>
<span class="nf">fi</span>
<span class="c"># becomes</span>
<span class="nf">if</span><span class="w"> </span><span class="nf">true</span>
<span class="w"> </span><span class="nf">echo</span><span class="w"> </span><span class="no">Yes</span><span class="w"> </span><span class="no">I</span><span class="w"> </span><span class="no">am</span><span class="w"> </span><span class="no">true</span>
<span class="nf">else</span>
<span class="w"> </span><span class="nf">echo</span><span class="w"> </span><span class="s2">"How is true not true?"</span>
<span class="nf">end</span>
<span class="nf">foo</span><span class="o">()</span><span class="w"> </span><span class="o">{</span>
<span class="no"> echo foo</span>
<span class="o">}</span>
<span class="c"># becomes</span>
<span class="nf">function</span><span class="w"> </span><span class="no">foo</span>
<span class="w"> </span><span class="nf">echo</span><span class="w"> </span><span class="no">foo</span>
<span class="nf">end</span>
<span class="c"># (bash allows the word "function",</span>
<span class="c"># but this is an extension)</span>
</pre></div>
</div>
<p>Fish does not have an <code class="docutils literal notranslate"><span class="pre">until</span></code>. Use <code class="docutils literal notranslate"><span class="pre">while</span> <span class="pre">not</span></code> or <code class="docutils literal notranslate"><span class="pre">while</span> <span class="pre">!</span></code>.</p>
</section>
<section id="subshells">
<h2>Subshells<a class="headerlink" href="#subshells" title="Link to this heading">¶</a></h2>
<p>Bash has a feature called “subshells”, where it will start another shell process for certain things. That shell will then be independent and e.g. any changes it makes to variables won’t be visible in the main shell.</p>
<p>This includes things like:</p>
<div class="highlight-sh notranslate"><div class="highlight"><pre><span></span><span class="c1"># A list of commands in `()` parentheses</span>
<span class="o">(</span>foo<span class="p">;</span><span class="w"> </span>bar<span class="o">)</span><span class="w"> </span><span class="p">|</span><span class="w"> </span>baz
<span class="c1"># Both sides of a pipe</span>
foo<span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="nb">read</span><span class="w"> </span>-r<span class="w"> </span>bar<span class="p">;</span><span class="w"> </span><span class="k">do</span>
<span class="w"> </span><span class="c1"># This will not be visible outside of the loop.</span>
<span class="w"> </span><span class="nv">VAR</span><span class="o">=</span>VAL
<span class="w"> </span><span class="c1"># This background process will not be, either</span>
<span class="w"> </span>baz<span class="w"> </span><span class="p">&</span>
<span class="k">done</span>
</pre></div>
</div>
<p>Fish does not currently have subshells. You will have to find a different solution. The isolation can usually be achieved by scoping variables (with <code class="docutils literal notranslate"><span class="pre">set</span> <span class="pre">-l</span></code>), but if you really do need to run your code in a new shell environment you can use <code class="docutils literal notranslate"><span class="pre">fish</span> <span class="pre">-c</span> <span class="pre">'your</span> <span class="pre">code</span> <span class="pre">here'</span></code> to do so explicitly.</p>
<p><code class="docutils literal notranslate"><span class="pre">()</span></code> subshells are often confused with <code class="docutils literal notranslate"><span class="pre">{}</span></code> grouping, which does <em>not</em> use a subshell. When you just need to group, you can use <code class="docutils literal notranslate"><span class="pre">begin;</span> <span class="pre">end</span></code> in fish:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="o">(</span><span class="nf">foo; bar</span><span class="o">)</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">baz</span>
<span class="c"># when it should really have been:</span>
<span class="nf">{</span><span class="w"> </span><span class="nf">foo</span><span class="p">;</span><span class="w"> </span><span class="nf">bar</span><span class="p">;</span><span class="w"> </span><span class="nf">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">baz</span>
<span class="c"># becomes</span>
<span class="nf">begin</span><span class="p">;</span><span class="w"> </span><span class="nf">foo</span><span class="p">;</span><span class="w"> </span><span class="nf">bar</span><span class="p">;</span><span class="w"> </span><span class="nf">end</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">baz</span>
</pre></div>
</div>
<p>The pipe will be run in the same process, so <code class="docutils literal notranslate"><span class="pre">while</span> <span class="pre">read</span></code> loops can set variables outside:</p>
<div class="highlight-fish-docs-samples notranslate"><div class="highlight"><pre><span></span><span class="nf">foo</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">while</span><span class="w"> </span><span class="nf">read</span><span class="w"> </span><span class="no">bar</span>
<span class="w"> </span><span class="nf">set</span><span class="w"> </span><span class="no">-g</span><span class="w"> </span><span class="no">VAR</span><span class="w"> </span><span class="no">VAL</span>
<span class="w"> </span><span class="nf">baz</span><span class="w"> </span><span class="p">&</span>
<span class="nf">end</span>
<span class="nf">echo</span><span class="w"> </span><span class="o">$VAR</span><span class="w"> </span><span class="c"># will print VAL</span>
<span class="nf">jobs</span><span class="w"> </span><span class="c"># will show "baz"</span>
</pre></div>
</div>
<p>Subshells are also frequently confused with <a class="reference internal" href="#bash-command-substitutions"><span class="std std-ref">command substitutions</span></a>, which bash writes as <code class="docutils literal notranslate"><span class="pre">`command`</span></code> or <code class="docutils literal notranslate"><span class="pre">$(command)</span></code> and fish writes as <code class="docutils literal notranslate"><span class="pre">$(command)</span></code> or <code class="docutils literal notranslate"><span class="pre">(command)</span></code>. Bash also <em>uses</em> subshells to implement them.</p>
</section>
<section id="builtins-and-other-commands">
<h2>Builtins and other commands<a class="headerlink" href="#builtins-and-other-commands" title="Link to this heading">¶</a></h2>
<p>By now it has become apparent that fish puts much more of a focus on its builtins and external commands rather than its syntax. So here are some helpful builtins and their rough equivalent in bash:</p>
<ul class="simple">
<li><p><a class="reference internal" href="cmds/string.html"><span class="doc">string</span></a> - this replaces most of the string transformation (<code class="docutils literal notranslate"><span class="pre">${i%foo}</span></code> et al) and can also be used instead of <code class="docutils literal notranslate"><span class="pre">grep</span></code> and <code class="docutils literal notranslate"><span class="pre">sed</span></code> and such.</p></li>
<li><p><a class="reference internal" href="cmds/math.html"><span class="doc">math</span></a> - this replaces <code class="docutils literal notranslate"><span class="pre">$((i</span> <span class="pre">+</span> <span class="pre">1))</span></code> arithmetic and can also do floats and some simple functions (sine and friends).</p></li>
<li><p><a class="reference internal" href="cmds/argparse.html"><span class="doc">argparse</span></a> - this can handle a script’s option parsing, for which bash would probably use <code class="docutils literal notranslate"><span class="pre">getopt</span></code> (zsh provides <code class="docutils literal notranslate"><span class="pre">zparseopts</span></code>).</p></li>
<li><p><a class="reference internal" href="cmds/count.html"><span class="doc">count</span></a> can be used to count things and therefore replaces <code class="docutils literal notranslate"><span class="pre">$#</span></code> and can be used instead of <code class="docutils literal notranslate"><span class="pre">wc</span></code>.</p></li>
<li><p><a class="reference internal" href="cmds/status.html"><span class="doc">status</span></a> provides information about the shell status, e.g. if it’s interactive or what the current linenumber is. This replaces <code class="docutils literal notranslate"><span class="pre">$-</span></code> and <code class="docutils literal notranslate"><span class="pre">$BASH_LINENO</span></code> and other variables.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">seq(1)</span></code> can be used as a replacement for <code class="docutils literal notranslate"><span class="pre">{1..10}</span></code> range expansion. If your OS doesn’t ship a <code class="docutils literal notranslate"><span class="pre">seq</span></code> fish includes a replacement function.</p></li>
</ul>
</section>
<section id="other-facilities">
<h2>Other facilities<a class="headerlink" href="#other-facilities" title="Link to this heading">¶</a></h2>
<p>Bash has <code class="docutils literal notranslate"><span class="pre">set</span> <span class="pre">-x</span></code> or <code class="docutils literal notranslate"><span class="pre">set</span> <span class="pre">-o</span> <span class="pre">xtrace</span></code> to print all commands that are being executed. In fish, this would be enabled by setting <span class="target" id="index-0"></span><a class="reference internal" href="language.html#envvar-fish_trace"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">fish_trace</span></code></a>.</p>
<p>Or, if your intention is to <em>profile</em> how long each line of a script takes, you can use <code class="docutils literal notranslate"><span class="pre">fish</span> <span class="pre">--profile</span></code> - see the <a class="reference internal" href="cmds/fish.html"><span class="doc">page for the fish command</span></a>.</p>
</section>
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