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Output colorization

As of version 6.0.0, Miller supports output-colorization. Here are examples using side-by-side black-background and white-background terminals:

Things having colors

• Keys in CSV header lines, JSON keys, etc
• Values in CSV data lines, JSON scalar values, etc
• "PASS" and "FAIL" in regression-test output
• Some online-help strings

Rules for colorization

• By default, colorize output only if writing to stdout and stdout is a TTY.

  • Example: color: mlr --csv cat foo.csv
  • Example: no color: mlr --csv cat foo.csv > bar.csv
  • Example: no color: mlr --csv cat foo.csv | less

• NIDX output format (plain text, Unix-style, with implicitly positionally indexed fields) is not colored. This is because in other formats, keys are one color and values are another. For NIDX, all output is values.

• The default colors were chosen since they look OK with white or black terminal background, and are differentiable with common varieties of human color vision.

Mechanisms for colorization

• Miller uses ANSI escape sequences only. This does not work on Windows except on Cygwin.
• Requires TERM environment variable to be set to non-empty string.
• Doesn't try to check to see whether the terminal is capable of 256-color ANSI vs 16-color ANSI. Note that if colors are in the range 0..15 then 16-color ANSI escapes are used, so this is in the user's control.

How you can control colorization

• Suppression/unsuppression:

  • export MLR_NO_COLOR=true means Miller won't color even when it normally would.
  • export MLR_ALWAYS_COLOR=true means Miller will color even when it normally would not. For example, you might want to use this when piping mlr output to less -r.
  • Command-line flags --no-color or -M, --always-color or -C.

• Color choices can be specified by using environment variables or command-line flags, with values 0..255:

  • export MLR_KEY_COLOR=208
  • export MLR_VALUE_COLOR=33
  • Likewise for MLR_PASS_COLOR, MLR_FAIL_COLOR, MLR_HELP_COLOR, MLR_REPL_PS1_COLOR, and MLR_REPL_PS2_COLOR.
  • Command-line flags --key-color 208, --value-color 33, etc., and likewise for --pass-color, --fail-color, --repl-ps1-color, --repl-ps2-color, and --help-color.
  • This is particularly useful if your terminal's background color clashes with current settings.

If environment-variable settings and command-line flags are both provided, the latter take precedence.

How to see available color codes

You can use mlr --list-color-codes to see the available color codes (like 170), and mlr --list-color-names to see available names (like orchid).