What is difference between grep -isn "String\.format" -R . and grep -isn String\.format -R .?
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What is difference between grep -isn "String\.format" -R . and grep -isn String\.format -R .?

When I use grep -isn String\.format -R ., the results includes String format and String.format; but if I use grep -isn "String\.format" -R . the results only includes String.format, this result is same as use grep -isn 'String\.format' -R ., can anyone give an explain?