Grep optional character

# You can use append \? to a capture group to make something optional:

grep -nri "^\s*\(public\|private\|protected\)\s*\(static\)\?\s*\(sub\|function\)" formName.frm

#In this case, the preceding group, which contains the string "static", is optional (i.e. may occur 0 or 1 times).

Source: stackoverflow.com

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