You can use samtools for this. Please check out in this link.

samtools flagstat RRBS_data.bam

No tool produces the exact same stats that you'd get when running the aligner (the output looks to be generated by bowtie )

But there are alternative tools designed to produce stats, for example bamstats

https://github.com/guigolab/bamstats

an output could look like this:

{
    "general": {
        "protocol": "SingleEnd",
        "reads": {
            "total": 101567,
            "unmapped": 7119,
            "mapped": {
                "0": 94448
            },
            "mappings": {
                "ratio": 1,
                "count": 94448
            }
        },
        "pairs": {}
    }
}