Editing Sed (section)

===sed used as a filter===
Under Unix, sed is often used as a [[filter (Unix)|filter]] in a [[pipeline (Unix)|pipeline]]:
<syntaxhighlight lang="console">
$ generateData | sed 's/x/y/g'
</syntaxhighlight>
That is, a program such as "generateData" generates data, and then sed makes the small change of replacing ''x'' with ''y''. For example:
<syntaxhighlight lang="console">
$ echo xyz xyz | sed 's/x/y/g'
yyz yyz
</syntaxhighlight>
<ref group="notes" name="quotes">
In command line use, the quotes around the expression are not required, and are only necessary if the shell would otherwise not interpret the expression as a single word (token). For the script <code>s/x/y/g</code> there is no ambiguity, so <code>generateData | sed s/x/y/g</code> works correctly. However, quotes are usually included for clarity, and are often necessary, notably for whitespace (e.g., <code>'s/x&nbsp;x/y&nbsp;y/'</code>). Most often single quotes are used, to avoid having the shell interpret <code>$</code> as a shell variable. Double quotes are used, such as <code>"s/$1/$2/g"</code>, to allow the shell to substitute for a command line argument or other shell variable.
</ref>