Hello.
I've come across what (to me) seems to be a problem with the FILENAME and FILENUM variables.

# mlr --version
Miller v5.6.2

# cat /tmp/csv1
A,B,C
_2GB,255,2
_4GB,120,4
_6GB,50,6
_10GB,10,10

# cat /tmp/csv2
FIRST,SECOND,THIRD,FOURTH
1,2,3,4
5,6,7,8
9,10,11,12
13,14,15,16

# mlr --icsv cat then put 'print FILENAME'   /tmp/csv1 /tmp/csv2
/tmp/csv1
A=_2GB,B=255,C=2
/

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