# Separators
## Record, field, and pair separators
Miller has record separators, field separators, and pair separators. For
example, given the following [DKVP](file-formats.md#dkvp-key-value-pairs)
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](file-formats.md) 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](file-formats.md#json), 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 (e.g. CSV input,
CSV output), or, to change them between input and output (e.g. CSV input, JSON
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:
cat data/a.dkvp
a=1,b=2,c=3
a=4,b=5,c=6
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.
cat data/modsep.dkvp
a:1;b:2;c:3
a:4;b:5;c:6
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 and regular-expression 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
As of September 2021:
* `IFS` and `IPS` can be regular expressions.
* `IRS` can be multi-character (except for file formats which don't allow parameterization -- see below)
* `OFS`, `OPS`, and `ORS` can be multi-character.
Since `IFS` and `IPS` can be regular expressions, if your data has field
separators which are one or more consecutive spaces, you can use `--ifs '(
)+'`. But that gets a little tedious, so Miller has the `--repifs` and
`--repips` flags you can use if you like. This wraps the `IFS` or `IPS`, say
`X`, as `(X)+`.
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
mlr --ifs ' ' --repifs --inidx --oxtab cat data/extra-spaces.txt
1 oh
2 say
3 can
4 you
1 see
2 by
3 the
4 dawn's
1 early
2 light
3 what
4 so
## Aliases
Many things we'd like to write as separators need to be escaped from the shell
-- e.g. `--ifs ';'` or `--ofs '|'`, and so on. You can use the following if you like:
mlr help list-separator-aliases
ascii_esc = "\x1b"
ascii_etx = "\x04"
ascii_fs = "\x1c"
ascii_gs = "\x1d"
ascii_null = "\x01"
ascii_rs = "\x1e"
ascii_soh = "\x02"
ascii_stx = "\x03"
ascii_us = "\x1f"
asv_fs = "\x1f"
asv_rs = "\x1e"
colon = ":"
comma = ","
cr = "\r"
crcr = "\r\r"
crlf = "\r\n"
crlfcrlf = "\r\n\r\n"
equals = "="
lf = "\n"
lflf = "\n\n"
newline = "\n"
pipe = "|"
semicolon = ";"
slash = "/"
space = " "
spaces = "( )+"
tab = "\t"
tabs = "(\t)+"
usv_fs = "\xe2\x90\x9f"
usv_rs = "\xe2\x90\x9e"
whitespace = "([ \t])+"
Note that `spaces`, `tabs`, and `whitespace` already are regexes so you
shouldn't use `--repifs` with them.
## Command-line flags
Given the above, we now have seen the following flags:
--rs --irs --ors
--fs --ifs --ofs --repifs
--ps --ips --ops
See also the [separator-flags section](reference-main-flag-list.md#separator-flags).
## DSL built-in variables
Miller exposes for you read-only [built-in variables](reference-dsl-variables.md#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 specified 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
Notes:
* If CSV field separator is tab, we have TSV; see more examples (ASV, USV, etc.) at in the [CSV section](file-formats.md#csvtsvasvusvetc).
* CSV IRS and ORS must be newline, and CSV IFS must be a single character. (CSV-lite does not have these restrictions.)
* JSON: ignores all separator flags from the command line.
* Headerless CSV overlaps quite a bit with NIDX format using comma for IFS. See also the page on [CSV with and without headers](csv-with-and-without-headers.md).
* For XTAB, the record separator is a repetition of the field separator. For example, if one record has `x=1,y=2` and the next has `x=3,y=4`, and OFS is newline, then output lines are `x 1`, then `y 2`, then an extra newline, then `x 3`, then `y 4`. This means: to customize XTAB, set `OFS` rather than `ORS`.
| | **RS** | **FS** | **PS** |
|------------|---------|---------|----------|
| [**CSV**](file-formats.md#csvtsvasvusvetc) | Always `\n`; not alterable * | Default `,`; must be single-character | None |
| [**TSV**](file-formats.md#csvtsvasvusvetc) | Always `\n`; not alterable * | Default `\t`; must be single-character | None |
| [**CSV-lite**](file-formats.md#csvtsvasvusvetc) | Default `\n` * | Default `,` | None |
| [**TSV-lite**](file-formats.md#csvtsvasvusvetc) | Default `\n` * | Default `\t` | None |
| [**JSON**](file-formats.md#json) | N/A; records are between `{` and `}` | Always `,`; not alterable | Always `:`; not alterable |
| [**DKVP**](file-formats.md#dkvp-key-value-pairs) | Default `\n` | Default `,` | Default `=` |
| [**NIDX**](file-formats.md#nidx-index-numbered-toolkit-style) | Default `\n` | Default space | None |
| [**XTAB**](file-formats.md#xtab-vertical-tabular) | Not used; records are separated by an extra FS | `\n` * | Default: space with repeats |
| [**PPRINT**](file-formats.md#pprint-pretty-printed-tabular) | Default `\n` * | Space with repeats | None |
| [**Markdown**](file-formats.md#markdown-tabular) | Always `\n`; not alterable * | One or more spaces, then `|`, then one or more spaces; not alterable | None |
\* or `\r\n` on Windows