Get the mapping statistics of a single read from a BAM file
samtools stats seems to be able to do most of this, excluding the CIGAR-string parsing stuff (i.e. INDELs):

$ samtools view -h mapped.bam | grep -e '^@' -e 'readName' |
    samtools stats | grep '^SN' | cut -f 2-

raw total sequences:    2
filtered sequences: 0
sequences:  2
is sorted:  1
1st fragments:  2
last fragments: 0
reads mapped:   2
reads mapped and paired:    0   # paired-end technology bit set + both mates mapped
reads unmapped: 0
reads properly paired:  0   # proper-pair bit set
reads paired:   0   # paired-end technology bit set
reads duplicated:   0   # PCR or optical duplicate bit set
reads MQ0:  0   # mapped and MQ=0
reads QC failed:    0
non-primary alignments: 0
total length:   13632   # ignores clipping
bases mapped:   13632   # ignores clipping
bases mapped (cigar):   13502   # more accurate
bases trimmed:  0
bases duplicated:   0
mismatches: 3670    # from NM fields
error rate: 2.718116e-01    # mismatches / bases mapped (cigar)
average length: 6816
maximum length: 6816
average quality:    8.9
insert size average:    0.0
insert size standard deviation: 0.0
inward oriented pairs:  0
outward oriented pairs: 0
pairs with other orientation:   0
pairs on different chromosomes: 0


For a length filter, an awk length check can be slotted in instead of the grep:

$ samtools view -h mapped.bam |
    awk -F'\t' '{if((/^@/) || (length($10)&gt;500)){print $0}}' |
    samtools stats | grep '^SN' | cut -f 2-

raw total sequences:    131
filtered sequences: 0
sequences:  131
is sorted:  1
1st fragments:  131
last fragments: 0
reads mapped:   131
reads mapped and paired:    0   # paired-end technology bit set + both mates mapped
reads unmapped: 0
reads properly paired:  0   # proper-pair bit set
reads paired:   0   # paired-end technology bit set
reads duplicated:   0   # PCR or optical duplicate bit set
reads MQ0:  0   # mapped and MQ=0
reads QC failed:    0
non-primary alignments: 0
total length:   569425  # ignores clipping
bases mapped:   569425  # ignores clipping
bases mapped (cigar):   453884  # more accurate
bases trimmed:  0
bases duplicated:   0
mismatches: 113755  # from NM fields
error rate: 2.506257e-01    # mismatches / bases mapped (cigar)
average length: 4346
maximum length: 16909
average quality:    9.1
insert size average:    0.0
insert size standard deviation: 0.0
inward oriented pairs:  0
outward oriented pairs: 0
pairs with other orientation:   0
pairs on different chromosomes: 0