在条件检查的末尾似乎缺少fi。

#!/bin/bash
listchange=$(git diff --name-only) 

echo "Check filenames:"

wrongfilenames=$(
    for filename in $listchange 
    do
        if [[ "$filename" = "strings.exe" ]]; then 
            echo "$filename"
            echo "has strings.exe"
            # TODO: take the appropriate action(s) here
            return 1 # => quit with error
        fi
    done
);
        
if [ -n "$wrongfilenames" ] ; then
    echo "The following files need not to commit:"
    echo "$wrongfilenames"
    echo "Commit rejected, fix it and try again."
    exit 1
else
    echo "....OK"
fi

注意：在检查字符串内容时，最好在$var前后加上双引号。实际上，如果$var有空格，它将无法正常工作。