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Command Line Interface (CLI)

All tools provided by MP must be standalone executables, installable into $PATH.

Those tools intended for run-time data processing (but not necessarily tools for training or deployment) are called processors. Processors must adhere to the following uniform interface, including mandatory and optional parameters (i.e. no more or fewer are permissible).

NOTE: Command line options cannot be repeated, except those explicitly marked as REPEATABLE (e.g. -p params.json -p '{"val": 1}' is allowed because -p is repeatable.

NOTE: Parameters marked MULTI-VALUE cannot be repeated but can specify multiple values, formatted as a single string with comma-separated items (e.g. -I group1,group2,group3 instead of -I group1 -I group2 -I group3).

CLI executable name

Every CLI executable’s name must begin with ocrd-.

Examples:

Mandatory parameters

-I, --input-file-grp GRP

MULTI-VALUE

METS file group(s) used as input.

Input file groups must not be modified.

Optional parameters

-O, --output-file-grp GRP

MULTI-VALUE

METS file group(s) used as output.

Omit to resort to default output file groups of the processor, or for processors that inherently do not produce output files.

-g, --page-id ID

MULTI-VALUE

The mets:div[@TYPE='page']/@ID that contains the mets:fptr/@FILEID pointers to files representing a page. Effectively, only those files in the input file group that are referenced in these mets:div[@TYPE="page"] will be processed.

Omit to process all pages.

--overwrite

Delete files in the output file group(s) before processing.

If --overwrite is set, but --page-id is not set, delete all output file groups set with --output-file-grp, including all files that belong to those file groups.

If --overwrite is set and --page-id is set, delete all files that represent any of the page IDs given with --page-id from all output file groups set with --output-file-grp

“File deletion” in the context of --overwrite means deletion of matching mets:file elements from the METS document and all local files these mets:file represent.

“Group deletion” in the context of --overwrite means deletion of the mets:fileGrp element from METS, and deletion of all files that belong to this mets:fileGrp element.

-p, --parameter PARAM_JSON

REPEATABLE

URL of parameter file in JSON format corresponding to the parameters section of the processor’s ocrd-tool metadata. If that file is not readable and PARAM_JSON begins with { (opening brace), try to parse PARAM_JSON as JSON. If that also fails, throw an exception.

When parsing JSON, all lines matching the regular expression ^\s*#.*, i.e. lines whose first non-whitespace character is #, are to be disregarded as comments.

When -p is repeated, the parsed values should be shallowly merged from right to left.

-p can be omitted to use default parameters only, or for processors without any parameters.

-P, --parameter-override KEY VAL

REPEATABLE

Companion to -p, --parameter PARAM_JSON that allows overriding KEY in the parameter JSON object with VAL. All P key-value-pairs are applied to the parameter JSON in the order they are given on the command line.

Syntactically, VAL SHOULD be a valid JSON datatype:

As a convenience, if VAL fails to parse as a valid JSON type, it is interpreted as a string (a string is equivalent to "a string", but true will be parsed as the boolean value true, not the string "true").

-m, --mets METS_IN

Input METS URL. Default: mets.xml

If METS_IN is a file path but the file is not readable, processors must show the --help message message and exit with return code 1.

-w, --working-dir DIR

Working Directory. Default: current working directory.

-l, --log-level LOGLEVEL

Set the global maximum verbosity level. More verbose log entries will be ignored. (One of OFF, ERROR, WARN, INFO (default), DEBUG, TRACE).

NOTE: Setting the log level via --log-level parameter should override any other implementation-specific means of logging configuration. For example, with --log-level TRACE no log messages should be filtered globally, whereas --log-level ERROR, only errors should be output globally.

-J, --dump-json

Instead of processing METS, output the ocrd-tool description for this executable, in particular its parameters.

-C, --show-resource FILENAME

Print the contents of processor resource FILENAME. Look up the resp. absolute filename according to the file parameter lookup rules.

-L, --list-resources

List the names of processor resources in all of the paths defined by.the file parameter lookup rules, one name per line.

-h, --help

Print a concise description of the tool, the command line options and parameters it accepts as well as the input/output groups. This information should be generated from ocrd-tool.json as much as possible.

Return value

Successful execution should signal 0. Any non-zero return value is considered a failure.

Logging

Data printed to STDERR and STDOUT is captured linewise and stored as log data.

Processors must adjust logging verbosity according to the --log-level parameter.

Errors, especially those leading to exceptions, must be printed to STDERR.

The log messages must have the format TIME LEVEL LOGGERNAME - MESSAGE\n, where

Processor resources

Parameters that reference files can be resolved from relative to absolute filename by following the conventions laid out in the ocrd_tool spec. These files, either bundled by the processor developer or put in place by the user, are called processor resources. The processor resources of a processor can be listed with the -L/--list-resources option and individual processor resources can be retrieved with the -C/--show-resource option. Since processor resources use the same mechanism as file parameters, they can be used

and the processor must resolve them to absolute paths according to the rules for file parameters.

URL/file convention

Whenever a URL is expected, it should be possible to use a local file path instead and have the implementation interpret as a file:// URL on the fly.

Implementations should adhere to this algorithm when resolving a URL u:

  1. If u contains the string ://: Do not modify.
  2. If u is an absolute path according to the mechanics of the underlying file system: Prepend file:// to u.
  3. Otherwise: Resolve u as a path relative to the current working directory, prepend file:// to u.

NOTE: This convention is limited to the CLI for convenience of users and developers. In METS and PAGE documents, URLs must be strictly valid and resolvable by common software agents as-is.

Example

This is how the CLI provided by the MP should work:

$> ocrd-kraken-binarize \
    --mets "file:///path/to/file/mets.xml" \
    --working-dir "file:///path/to/workingDir/" \
    --parameters "file:///path/to/file/parameters.json" \
    --page-id PHYS_0001,PHYS_0002,PHYS_0003 \
    --input-file-grp OCR-D-IMG
    --output-file-grp OCR-D-IMG-BIN-KRAKEN

And this is how it will be called with the ocrd process CLI:

$> ocrd process \
    'kraken-binarize -I OCR-D-IMG -O OCR-D-IMG-BIN-KRAKEN -p /path/to/file/parameters.json'
    -m "file:///path/to/file/mets.xml" \
    -g PHYS_0001,PHYS_0002,PHYS_0003

    preprocessing/binarization/kraken-binarize

METS input

<mets:mets>
    <!-- ... -->
  <mets:structMap TYPE="PHYSICAL">
    <mets:div ID="PHYS_0000" TYPE="physSequence">
      <mets:div TYPE="page" ID="PHYS_0001">
        <mets:fptr FILEID="OCR-D-IMG_0001"/>
      </mets:div>
      <mets:div TYPE="page" ID="PHYS_0002">
        <mets:fptr FILEID="OCR-D-IMG_0002"/>
      </mets:div>
      <mets:div TYPE="page" ID="PHYS_0003">
        <mets:fptr FILEID="OCR-D-IMG_0003"/>
      </mets:div>
    </mets:div>
  </mets:structMap>

  <mets:fileSec>

    <mets:fileGrp USE="OCR-D-IMG">
      <mets:file ID="OCR-D-IMG_0001" MIMETYPE="image/tiff">
        <mets:FLocat LOCTYPE="URL" xlink:href="https://github.com/OCR-D/spec/raw/master/io/example/00000001.tif" />
      </mets:file>
      <mets:file ID="OCR-D-IMG_0002" MIMETYPE="image/tiff">
        <mets:FLocat LOCTYPE="URL" xlink:href="https://github.com/OCR-D/spec/raw/master/io/example/00000002.tif" />
      </mets:file>
      <mets:file ID="OCR-D-IMG_0003" MIMETYPE="image/tiff">
        <mets:FLocat LOCTYPE="URL" xlink:href="https://github.com/OCR-D/spec/raw/master/io/example/00000003.tif" />
      </mets:file>
    </mets:fileGrp>

  </mets:fileSec>
</mets:mets>

Input JSON parameter file

{
    "threshold": 0.05,
    "zoom": 2,
    "range": [5, 10],
}

METS output

This is the METS file after being run through the MP CLI:

<mets:mets>
    <!-- ... -->
  <mets:structMap TYPE="PHYSICAL">
    <mets:div DMDID="DMDPHYS_0000" ID="PHYS_0000" TYPE="physSequence">
      <mets:div TYPE="page" ID="PHYS_0001">
        <mets:fptr FILEID="OCR-D-IMG_0001"/>
        <mets:fptr FILEID="OCR-D-IMG-BIN-KRAKEN_0001"/>
      </mets:div>
      <mets:div TYPE="page" ID="PHYS_0002">
        <mets:fptr FILEID="OCR-D-IMG_0002"/>
        <mets:fptr FILEID="OCR-D-IMG-BIN-KRAKEN_0002"/>
      </mets:div>
      <mets:div TYPE="page" ID="PHYS_0003">
        <mets:fptr FILEID="OCR-D-IMG_0003"/>
        <mets:fptr FILEID="OCR-D-IMG-BIN-KRAKEN_0003"/>
      </mets:div>
    </mets:div>
  </mets:structMap>

  <mets:fileSec>

    <mets:fileGrp USE="OCR-D-IMG">
      <mets:file ID="OCR-D-IMG_0001" MIMETYPE="image/tiff">
        <mets:FLocat LOCTYPE="URL" xlink:href="https://github.com/OCR-D/spec/raw/master/io/example/00000001.tif" />
      </mets:file>
      <mets:file ID="OCR-D-IMG_0002" MIMETYPE="image/tiff">
        <mets:FLocat LOCTYPE="URL" xlink:href="https://github.com/OCR-D/spec/raw/master/io/example/00000002.tif" />
      </mets:file>
      <mets:file ID="OCR-D-IMG_0003" MIMETYPE="image/tiff">
        <mets:FLocat LOCTYPE="URL" xlink:href="https://github.com/OCR-D/spec/raw/master/io/example/00000003.tif" />
      </mets:file>
    </mets:fileGrp>

    <mets:fileGrp USE="OCR-D-IMG-BIN-KRAKEN">
      <mets:file ID="OCR-D-IMG-BIN-KRAKEN_0001" MIMETYPE="image/png">
        <mets:FLocat LOCTYPE="URL" xlink:href="file:///tmp/ocrd-workspace-ABC123/0001.png" />
      </mets:file>
      <mets:file ID="OCR-D-IMG-BIN-KRAKEN_0002" MIMETYPE="image/png">
        <mets:FLocat LOCTYPE="URL" xlink:href="file:///tmp/ocrd-workspace-ABC123/0002.png" />
      </mets:file>
      <mets:file ID="OCR-D-IMG-BIN-KRAKEN_0003" MIMETYPE="image/png">
        <mets:FLocat LOCTYPE="URL" xlink:href="file:///tmp/ocrd-workspace-ABC123/0003.png" />
      </mets:file>
    </mets:fileGrp>

  </mets:fileSec>
</mets:mets>