+= to assign (or quote '+=' if
literal).var += "my text"var+="my text"ShellCheck found an unquoted += after a word. To append
text to a variable, remove spaces around += as in the
example.
If the += was supposed to be literal, you can quote it
to make ShellCheck ignore it:
grep '+=' files..
ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.