我不明白 ls [aDt]*t?t 的含义

Question

Probably a quick and easy one for you guys but I can't actually find an answer anywhere.

What does this mean? Break it down for me, please?

Answer 1

The naswer is simple:

• [aDt] : the character a or D or t .
• * : zero or more (any) characters.
• . : the dot.
• t : the t character.
• ? : any (single) character.
• t : the t character.

Answer 2

"[aDt]*.t?t" is an expression of the "shell expansion" (there are several types, this one is "pattern matching").

This expansions use wildcard-type items to match not only a single name, but multiple.

In the case of ls command (your question, but the same applies to any command), it will list all the files having a matching name, but not other files.

[aDt]  matches any of the character "a", "D", "t"
*      matches any number (even zero) of any character
?      matches any single character

This expression can match, for example

  D-data.txt
  a-what.tNt
  t.tst

but not

  mega.txt      (first letter is not a, D or t)
  ciao.TXT      (the uppercase T of TXT do not match)
  ciaotxt       (does not contain a dot)

This is only a partial reply, things are much more complicated.