What causes regex to fail to compile in Bash?

What causes regex to fail to compile in Bash?

So if you write: [ [ $x =~ [$0-9a-zA-Z] ]], the $0 inside the regex on the right will be expanded before the regex is interpreted, which will probably cause the regex to fail to compile (unless the expansion of $0 ends with a digit or punctuation symbol whose ascii value is less than a digit).

How to do regex matching in bash [ example ]?

Example # 1 The [ [ $s =~ $pat ]] construct performs the regex matching 2 The captured groups i.e the match results are available in an array named BASH_REMATCH 3 The 0th index in the BASH_REMATCH array is the total match 4 The i’th index in the BASH_REMATCH array is the i’th captured group, where i = 1, 2, 3 More

What does ” does not match ” mean in Bash?

! negates the test, turning it into a “does not match” operator, and a [^…] regex character class means “any character other than “. The combination of parameter expansion and regex operators can make bash regular expression syntax “almost readable”, but there are still some gotchas. (Aren’t there always?)

Can you use regex in Bash < 3.2?

Regex are not supported for version of bash <3.2 (as dennis mentioned), but you can still use extended globbing (by setting extglob ). for extended globbing, see here and some simple examples here. Update for OP: Example to find files that start with 2 characters (the dots “.”

Can you match strings with regex in Bash?

Trying to match any string that contains spaces, lowercase, uppercase, or numbers. Special characters would be nice too, but I think that requires escaping certain characters. This obviously only tests for upper, lower, numbers, and spaces.

Are there any Gotchas with regex in Bash?

The combination of parameter expansion and regex operators can make bash regular expression syntax “almost readable”, but there are still some gotchas. (Aren’t there always?) One is that you could not put ] into $valid, even if $valid were quoted, except at the very beginning.