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Short format specifiers, including --c2p

In our examples so far we've often made use of mlr --icsv --opprint or mlr --icsv --ojson. These are such frequently occurring patterns that they have short options like --c2p and --c2j:

mlr --c2p head -n 2 example.csv
color  shape    flag k index quantity rate
yellow triangle true 1 11    43.6498  9.8870
red    square   true 2 15    79.2778  0.0130
mlr --c2j head -n 2 example.csv
  "color": "yellow",
  "shape": "triangle",
  "flag": "true",
  "k": 1,
  "index": 11,
  "quantity": 43.6498,
  "rate": 9.8870
  "color": "red",
  "shape": "square",
  "flag": "true",
  "k": 2,
  "index": 15,
  "quantity": 79.2778,
  "rate": 0.0130

You can get the full list here.

File names up front, including --from

Already we saw that you can put the filename first using --from. When you're interacting with your data at the command line, this makes it easier to up-arrow and append to the previous command:

mlr --c2p --from example.csv sort -nr index then head -n 3
color  shape  flag  k  index quantity rate
purple square false 10 91    72.3735  8.2430
yellow circle true  9  87    63.5058  8.3350
yellow circle true  8  73    63.9785  4.2370
mlr --c2p --from example.csv sort -nr index then head -n 3 then cut -f shape,quantity
shape  quantity
square 72.3735
circle 63.5058
circle 63.9785

If there's more than one input file, you can use --mfrom, then however many file names, then -- to indicate the end of your input-file-name list:

mlr --c2p --mfrom data/*.csv -- sort -n index

Alternatively, you may place filenames within another file, one per line:

cat data/filenames.txt
mlr --c2p --files data/filenames.txt cat

Shortest flags for CSV, TSV, and JSON

The following have even shorter versions:

  • -c is the same as --csv
  • -t is the same as --tsv
  • -j is the same as --json

I don't use these within these documents, since I want the docs to be self-explanatory on every page, and I think mlr --csv ... explains itself better than mlr -c .... Nonetheless, they're always there for you to use.

.mlrrc file

If you want the default file format for Miller to be CSV, you can simply put --csv on a line by itself in your ~/.mlrrc file. Then instead of mlr --csv cat example.csv you can just do mlr cat example.csv. This is just a personal default, though, so mlr --opprint cat example.csv will use default CSV format for input, and PPRINT (tabular) for output.

You can read more about this at the Customization page.

Scripts and mlr -s

Suppose you are often doing something like

mlr --csv \
filter ‘$quantity > 100’ then \
count-distinct -f category then \
fraction -f count \

Typing this out can get a bit old, if the only thing that changes for you is the filename.

See Scripting with Miller for some keystroke-saving options.