Suppose you always use CSV files. Then instead of always having to type --csv as in

mlr --csv cut -x -f extra mydata.csv

mlr --csv sort -n id mydata.csv

and so on, you can instead put the following into your $HOME/.mlrrc:

--csv

Then you can just type things like

mlr cut -x -f extra mydata.csv

mlr sort -n id mydata.csv

and the --csv part will automatically be understood. (If you do want to process, say, a JSON file then mlr --json ... at the command line will override the default from your .mlrrc.)

• You can include any command-line flags, except the "terminal" ones such as --help.
• The formatting rule is you need to put one flag beginning with -- per line: for example, --csv on one line and --nr-progress-mod 1000 on a separate line.
• Since every line starts with a -- option, you can leave off the initial -- if you want. For example, ojson is the same as --ojson, and nr-progress-mod 1000 is the same as --nr-progress-mod 1000.
• Comments are from a # to the end of the line.
• Empty lines are ignored -- including lines which are empty after comments are removed.

Here is an example .mlrrc file:

# These are my preferred default settings for Miller

# Input and output formats are CSV by default (unless otherwise specified
# on the mlr command line):
csv

# If a data line has fewer fields than the header line, instead of erroring
# (which is the default), just insert empty values for the missing ones:
allow-ragged-csv-input

# These are no-ops for CSV, but when I do use JSON output, I want these
# pretty-printing options to be used:
jvstack
jlistwrap

# Use "@", rather than "#", for comments within data files:
skip-comments-with @

• If the environment variable MLRRC is set:
• If its value is __none__ then no .mlrrc files are processed. (This is nice for things like regression testing.)
• Otherwise, its value (as a filename) is loaded and processed. If there are syntax errors, they abort mlr with a usage message (as if you had mistyped something on the command line). If the file can't be loaded at all, though, it is silently skipped.
• Any .mlrrc in your home directory or current directory is ignored whenever MLRRC is set in the environment.
• Example line in your shell’s rc file: export MLRRC=/path/to/my/mlrrc
• Otherwise:
  • If $HOME/.mlrrc exists, it’s processed as above.
  • If ./.mlrrc exists, it’s then also processed as above.
  • The idea is you can have all your settings in your $HOME/.mlrrc, then override maybe one or two for your current directory if you like.