bash regular expression different formats

Question

I have used regular expression in my code like this: .*[^0-9].*

But recently I have seen some functions implemented like this: *[!0-9]* for the same purpose of first example, that is non-integer numbers.

So I confused what is the true form of regex and what is the difference of them.

can anybody help me in this issue?

Answer 1

There is only one regular expression - the first one. The second one is a glob pattern.

See regex(7) for the description of POSIX extended regular expressions supported by Bash: http://man7.org/linux/man-pages/man7/regex.7.html

See Bash manual for the description of glob patterns: http://www.gnu.org/software/bash/manual/html_node/Pattern-Matching.html

Bash uses regular expressions in [[…]] command only: http://www.gnu.org/software/bash/manual/html_node/Conditional-Constructs.html

Bash uses glob patterns for everything else.