Regex capture every occurrence of a word within two delimiters

Question

Say I have a long string of text, and I want to capture every time the word this is mentioned within rounded brackets. How could I do that? The following patt

Answer 1

I implemented the regex to enclose all alphanumberic characters using regex below:

# cat testfile 
aabc a1 +++    xyz 20   30 =40  -r
# cat testfile | sed -e "s/\([[:alnum:]]\{1,\}\)/
\1/g"
aabc 
a1 +++    
xyz 
20   
30 =
40  -
r
#


Hope it helps.