miller/docs6/docs/reference-main-separators.md

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# Separators

Record, field, and pair separators

Miller has record separators, field separators, and pair separators. For example, given the following DKVP records:

cat data/a.dkvp

a=1,b=2,c=3
a=4,b=5,c=6

• the record separator is newline -- it separates records from one another;
• the field separator is , -- it separates fields (key-value pairs) from one another;
• and the pair separator is = -- it separates the key from the value within each key-value pair.

These are the default values, which you can override with flags such as --ips and --ops (below).

Not all file formats have all three of these: for example, CSV does not have a pair separator, since keys are on the header line and values are on each data line.

Also, separators are not programmable for all file formats. For example, in JSON objects, the pair separator is : and the field-separator is , -- we write {"a":1,"b":2,"c":3} -- but these aren't modifiable. If you do mlr --json --ips : --ips '=' cat myfile.json then you don't get {"a"=1,"b"=2,"c"=3}. This is because the pair-separator : is part of the JSON specification.

Input and output separators

Miller lets you use the same separators for input and output, or, to change them between input and output, if you wish to transform your data in that way.

Miller uses the names IRS and ORS for the input and output record separators, IFS and OFS for the input and output field separators, and IPS and OPS for input and output pair separators.

For example:

mlr --ifs , --ofs ';' --ips = --ops : cut -o -f c,a,b data/a.dkvp

c:3;a:1;b:2
c:6;a:4;b:5

If your data has non-default separators and you don't want to change those between input and output, you can use --rs, --fs, and --ps. Setting --fs : is the same as setting --ifs : --ofs :, but with fewer keystrokes.

mlr --fs ';' --ps : cut -o -f c,a,b data/modsep.dkvp

c:3;a:1;b:2
c:6;a:4;b:5

Multi-character separators

The separators default to single characters, but can be multiple characters if you like:

mlr --ifs ';' --ips : --ofs ';;;' --ops := cut -o -f c,a,b data/modsep.dkvp

c:=3;;;a:=1;;;b:=2
c:=6;;;a:=4;;;b:=5

While the separators can be multiple characters, regular expressions (which Miller supports in many ways) are not (as of mid-2021) supported by Miller. So, in the above example, you can say the field-separator is one semicolon, or three, but two or four won't be recognized using --ifs ';;;'.

To fill this need, in the absence of full regular-expression support, Miller has a --repifs option for input. This means, for example, using --ifs ' ' --repifs you can have the field separator be one or more spaces. (Mixes of spaces and tabs, however, won't be recognized as a separator.)

The --repifs flag means that multiple successive occurrences of the field separator count as one. For example, in CSV data we often signify nulls by empty strings, e.g. 2,9,,,,,6,5,4. On the other hand, if the field separator is a space, it might be more natural to parse 2 4 5 the same as 2 4 5: --repifs --ifs ' ' lets this happen. In fact, the --ipprint option above is internally implemented in terms of --repifs.

For example:

cat data/extra-spaces.txt

oh    say   can you
see   by    the dawn's
early light what so

(TODO: FIXME)

mlr --ifs ' ' --repifs --inidx --oxtab cat  data/extra-spaces.txt

1 oh
2 
3 
4 
5 say
6 
7 
8 can
9 you

1 see
2 
3 
4 by
5 
6 
7 
8 the
9 dawn's

1 early
2 light
3 what
4 so

Command-line flags

Given the above, we now have seen the following flags:

--rs --irs --ors
--fs --ifs --ofs --repifs
--ps --ips --ops

Also note that you can use names for certain characters: e.g. --fs space is the same as --fs ' '. A full list is: colon, comma, equals, newline, pipe, semicolon, slash, space, tab.

DSL built-in variables

Miller exposes for you read-only built-in variables with names IRS, ORS, IFS, OFS, IPS, and OPS. Unlike in AWK, you can't set these in begin-blocks -- their values indicate what you set at the command line -- so their use is limited.

mlr --ifs , --ofs ';' --ips = --ops : --from data/a.dkvp put '$d = ">>>" . IFS . "|||" . OFS . "<<<"'

a:1;b:2;c:3;d:>>>,|||;<<<
a:4;b:5;c:6;d:>>>,|||;<<<

Which separators apply to which file formats

• CSV/TSV/ASV/USV/etc.:
  • Record separator is newline (Linux/BSDs/MacOS) or carriage-return-newline (Windows); programmable in Miller 5 and below; TODO to support for the Miller 6 release.
  • If field separator is tab, we have TSV; see more examples (ASV, USV, etc.) at in the CSV section.
  • No pair separator.
• JSON: ignores all separator flags from the command line.
• PPRINT
  • Record separator is newline (Linux/BSDs/MacOS) or carriage-return-newline (Windows); programmable in Miller 5 and below; TODO to support for the Miller 6 release.
  • TODO: write up
  • TODO: write up
• Markdown tabular: ignores all separator flags from the command line.
• XTAB
  • TODO: write up
  • TODO: write up
  • TODO: write up
• DKVP: lets you specify record, field, and pair separators.
• NIDX
  • TODO: write up
  • TODO: write up
  • No pair separator.