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* Docs6 proofreads batch 3 * BUild-everything script for local development * Start of glossary * Put quicklinks atop every page, not just the base-index page * Expanded record-heterogeneity page * streaming page * separators page * vimrc doc * separators page
136 lines
5.2 KiB
Markdown
136 lines
5.2 KiB
Markdown
# Separators
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## Record, field, and pair separators
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Miller has record separators, field separators, and pair separators. For
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example, given the following [DKVP](file-formats.md#dkvp-key-value-pairs)
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records:
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GENMD_RUN_COMMAND
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cat data/a.dkvp
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GENMD_EOF
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* the **record separator** is newline -- it separates records from one another;
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* the **field separator** is `,` -- it separates fields (key-value pairs) from one another;
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* and the **pair separator** is `=` -- it separates the key from the value within each key-value pair.
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These are the default values, which you can override with flags such as `--ips`
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and `--ops` (below).
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Not all [file formats](file-formats.md) have all three of these: for example,
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CSV does not have a pair separator, since keys are on the header line and
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values are on each data line.
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Also, separators are not programmable for all file formats. For example, in
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[JSON objects](file-formats.md#json), the pair separator is `:` and the
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field-separator is `,` -- we write `{"a":1,"b":2,"c":3}` -- but these aren't
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modifiable. If you do `mlr --json --ips : --ips '=' cat myfile.json` then you
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don't get `{"a"=1,"b"=2,"c"=3}`. This is because the pair-separator `:` is
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part of the JSON specification.
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## Input and output separators
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Miller lets you use the same separators for input and output, or, to change
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them between input and output, if you wish to transform your data in that way.
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Miller uses the names `IRS` and `ORS` for the input and output record
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separators, `IFS` and `OFS` for the input and output field separators, and
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`IPS` and `OPS` for input and output pair separators.
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For example:
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GENMD_RUN_COMMAND
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mlr --ifs , --ofs ';' --ips = --ops : cut -o -f c,a,b data/a.dkvp
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GENMD_EOF
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If your data has non-default separators and you don't want to change those
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between input and output, you can use `--rs`, `--fs`, and `--ps`. Setting `--fs
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:` is the same as setting `--ifs : --ofs :`, but with fewer keystrokes.
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GENMD_RUN_COMMAND
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mlr --fs ';' --ps : cut -o -f c,a,b data/modsep.dkvp
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GENMD_EOF
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## Multi-character separators
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The separators default to single characters, but can be multiple characters if you like:
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GENMD_RUN_COMMAND
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mlr --ifs ';' --ips : --ofs ';;;' --ops := cut -o -f c,a,b data/modsep.dkvp
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GENMD_EOF
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While the separators can be multiple characters, [regular
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expressions](reference-main-regular-expressions.md) (which Miller supports in
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many ways) are not (as of mid-2021) supported by Miller. So, in the above
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example, you can say the field-separator is one semicolon, or three, but two or
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four won't be recognized using `--ifs ';;;'`.
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To fill this need, in the absence of full regular-expression support, Miller
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has a `--repifs` option for input. This means, for example, using `--ifs
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' ' --repifs` you can have the field separator be one _or more_ spaces. (Mixes
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of spaces and tabs, however, won't be recognized as a separator.)
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The `--repifs` flag means that multiple successive occurrences of the field
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separator count as one. For example, in CSV data we often signify nulls by
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empty strings, e.g. `2,9,,,,,6,5,4`. On the other hand, if the field separator
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is a space, it might be more natural to parse `2 4 5` the same as `2 4 5`:
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`--repifs --ifs ' '` lets this happen. In fact, the `--ipprint` option above
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is internally implemented in terms of `--repifs`.
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For example:
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GENMD_RUN_COMMAND
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cat data/extra-spaces.txt
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GENMD_EOF
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(TODO: FIXME)
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GENMD_RUN_COMMAND
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mlr --ifs ' ' --repifs --inidx --oxtab cat data/extra-spaces.txt
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GENMD_EOF
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## Command-line flags
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Given the above, we now have seen the following flags:
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GENMD_CARDIFY
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--rs --irs --ors
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--fs --ifs --ofs --repifs
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--ps --ips --ops
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GENMD_EOF
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Also note that you can use names for certain characters: e.g. `--fs space` is
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the same as `--fs ' '`. A full list is: `colon`, `comma`, `equals`, `newline`,
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`pipe`, `semicolon`, `slash`, `space`, `tab`.
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## DSL built-in variables
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Miller exposes for you read-only [built-in variables](reference-dsl-variables.md#built-in-variables) with
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names `IRS`, `ORS`, `IFS`, `OFS`, `IPS`, and `OPS`. Unlike in AWK, you can't set these in begin-blocks --
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their values indicate what you set at the command line -- so their use is limited.
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GENMD_RUN_COMMAND
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mlr --ifs , --ofs ';' --ips = --ops : --from data/a.dkvp put '$d = ">>>" . IFS . "|||" . OFS . "<<<"'
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GENMD_EOF
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## Which separators apply to which file formats
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* CSV/TSV/ASV/USV/etc.:
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* 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.
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* If field separator is tab, we have TSV; see more examples (ASV, USV, etc.) at in the [CSV section](file-formats.md#csvtsvasvusvetc).
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* No pair separator.
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* JSON: ignores all separator flags from the command line.
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* PPRINT
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* 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.
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* TODO: write up
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* TODO: write up
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* Markdown tabular: ignores all separator flags from the command line.
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* XTAB
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* TODO: write up
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* TODO: write up
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* TODO: write up
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* DKVP: lets you specify record, field, and pair separators.
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* NIDX
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* TODO: write up
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* TODO: write up
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* No pair separator.
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