03. Matching single characters

Using literal characters

Let's start by matching a single character. The most obvious way would be to use a literal character for alphabetic letters. If there is a metacharacter that you would like to match, you can escape it with the backslash (\).

$ ls /usr/bin | grep 'c\.d'
creatbyproc.d filebyproc.d newproc.d pidpersec.d runocc.d syscallbyproc.d syscallbysysc.d

Here's a simple regex example. We are looking for patterns that has a c, followed by a period (.), then a d.

From this we can notice two things:

  • We need to use the backslash to escape metacharacters (the period).
  • Order matters.
  • This isn't a "fuzzy search", where cat can match something like combat.

Using dot metacharacter

The dot (.) metacharacter matches any single character.

$ ls /usr/bin/ | grep 'c.t'
bzcat codesign_allocate colcrt cut gencat gzcat locate policytool tccutil xmlcatalog ypcat zcat

Notice how a character must be present within between c and t. The dot metacharacter does not allow for the NUL character.

In the next section, we'll learn how to use bracket expansions, which will give you even more power in selecting single characters.

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