[regex] Regular expression to extract text between square brackets

if you want fillter only small alphabet letter between square bracket a-z

(\[[a-z]*\])

if you want small and caps letter a-zA-Z

(\[[a-zA-Z]*\]) 

if you want small caps and number letter a-zA-Z0-9

(\[[a-zA-Z0-9]*\]) 

if you want everything between square bracket

if you want text , number and symbols

(\[.*\])