Pattern: Use of brace expansion in [ ]
Issue: -
Brace expansions in [ ] will expand to a sequence of words. Operators work on single words.
Example of incorrect code:
[ "$file" = index.{htm,html,php} ] && echo "This is the main file"
This is equivalent to [ "$file" = index.htm index.html index.php ], which is invalid syntax. A typical error message is bash: [: too many arguments or dash: somefile: unexpected operator.
Instead, use a for loop to iterate over values, and apply your condition to each.
Example of correct code:
for main in index.{htm,html,php}
do
[ "$file" = "$main" ] && echo "This is the main file"
done