=~ is for regex, but this looks like a glob. Use = instead.

Problematic code:

[[ $file =~ *.txt ]]

Correct code:

[[ $file = *.txt ]]

Rationale:

You are using =~ to match against a regex -- specifically a Extended Regular Expression (ERE) -- but the right-hand side looks more like a glob:

• It may have a leading *, like in *.txt

  • In a glob, this matches strings ending in .txt, like readme.txt but not foo.sh
  • In an ERE, this matches a literal asterisk, followed by any character, and then txt, such as *itxt but not test.txt

• It may be a single letter followed by a *, like in s*.

  • In a glob, this matches strings starting with s, such as shell and set.
  • In an ERE, this matches zero or more ss, such as dog (because it does in fact contain zero or more s's)

Please ensure that the pattern is correct as an ERE, or switch to glob matching if that's what you intended.

This is similar to SC2063, where grep "*foo*" produces an equivalent warning.

Exceptions:

If you are aware of the difference, you can ignore this message, but this warning is not emitted for the more probable EREs \*.txt, \.txt$, ^s or s+, so it should rarely be necessary.

Related resources:

• Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!