Reference: data types¶

Miller’s input and output are all string-oriented: there is (as of August 2015 anyway) no support for binary record packing. In this sense, everything is a string in and out of Miller. During processing, field names are always strings, even if they have names like “3”; field values are usually strings. Field values’ ability to be interpreted as a non-string type only has meaning when comparison or function operations are done on them. And it is an error condition if Miller encounters non-numeric (or otherwise mistyped) data in a field in which it has been asked to do numeric (or otherwise type-specific) operations.

Field values are treated as numeric for the following:

Numeric sort: mlr sort -n, mlr sort -nr.
Statistics: mlr histogram, mlr stats1, mlr stats2.
Cross-record arithmetic: mlr step.

For mlr put and mlr filter:

Miller’s types for function processing are empty-null (empty string), absent-null (reads of unset right-hand sides, or fall-through non-explicit return values from user-defined functions), error, string, float (double-precision), int (64-bit signed), and boolean.
On input, string values representable as numbers, e.g. “3” or “3.1”, are treated as int or float, respectively. If a record has x=1,y=2 then mlr put '$z=$x+$y' will produce x=1,y=2,z=3, and mlr put '$z=$x.$y' does not give an error simply because the dot operator has been generalized to stringify non-strings. To coerce back to string for processing, use the string function: mlr put '$z=string($x).string($y)' will produce x=1,y=2,z=12.
On input, string values representable as boolean (e.g. "true", "false") are not automatically treated as boolean. (This is because "true" and "false" are ordinary words, and auto string-to-boolean on a column consisting of words would result in some strings mixed with some booleans.) Use the boolean function to coerce: e.g. giving the record x=1,y=2,w=false to mlr put '$z=($x<$y) || boolean($w)'.
Functions take types as described in mlr --help-all-functions: for example, log10 takes float input and produces float output, gmt2sec maps string to int, and sec2gmt maps int to string.
All math functions described in mlr --help-all-functions take integer as well as float input.

String literals¶

You can use the following backslash escapes for strings such as between the double quotes in contexts such as mlr filter '$name =~ "..."', mlr put '$name = $othername . "..."', mlr put '$name = sub($name, "...", "..."), etc.:

\a: ASCII code 0x07 (alarm/bell)
\b: ASCII code 0x08 (backspace)
\f: ASCII code 0x0c (formfeed)
\n: ASCII code 0x0a (LF/linefeed/newline)
\r: ASCII code 0x0d (CR/carriage return)
\t: ASCII code 0x09 (tab)
\v: ASCII code 0x0b (vertical tab)
\\: backslash
\": double quote
\123: Octal 123, etc. for \000 up to \377
\x7f: Hexadecimal 7f, etc. for \x00 up to \xff

These replacements apply only to strings you key in for the DSL expressions for filter and put: that is, if you type \t in a string literal for a filter/put expression, it will be turned into a tab character. If you want a backslash followed by a t, then please type \\t.

However, these replacements are not done automatically within your data stream. If you wish to make these replacements, you can do, for example, for a field named field, mlr put '$field = gsub($field, "\\t", "\t")'. If you need to make such a replacement for all fields in your data, you should probably simply use the system sed command.