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Placeholders

Juggling longs paths in command-lines can be nightmare, which is the reason the spectral-data-converter library offers support for placeholders. Placeholders can be used to shorten paths and making command-lines easier to transfer to another environment or user. Placeholders (format {PH}) get expanded dynamically at runtime, taking the current state into account.

Placeholder types#

There are different types of placeholders:

  • System-defined ones:

    • {HOME} - the user's home directory
    • {CWD} - the current working directory
    • {TMP} - the temporary directory

  • Input-based ones, which are based on the current input file being processed:

    • {INPUT_PATH} - the directory component of the current file
    • {INPUT_NAMEEXT} - the name (incl ext) of the current file
    • {INPUT_NAMENOEXT} - the name (excl ext) of the current file
    • {INPUT_EXT} - the extension of the current file
    • {INPUT_PARENT_PATH} - the path of the file's parent
    • {INPUT_PARENT_NAME} - the name of the file's parent

  • User-defined ones, which are supplied to the tool itself, e.g., via the -p/--placeholders option of the sdc-convert tool. The same script can be executed using different directories when using different placeholder setups. The format for the placeholders files is simple, one placeholder per line using placeholder=value as format. Empty lines and ones starting with # get ignored.

  • Runtime ones, which can be set with the set-placeholder plugin. These placeholders can be based on other placeholders. The reason for this plugin is that the output of some filters may not have any directory associated with them anymore, only a file name. That renders all the input-based placeholders unusable. Using set-placeholder beforehand allows saving the input directory in another placeholder for later use. Meta-data can be used as placeholders as well using the metadata-to-placeholder plugin, which extracts a particular key from the metadata passing through and updates the specified placeholder accordingly.

Examples#

Relative to input#

The following command places the converted data on the same level as the input directory adams in a directory called asc:

sdc-convert \
  -l INFO \
  from-adams \
    -l INFO \
    -i "/some/where/adams/*.spec" \
    --labels a b c \
  to-asc \
    -l INFO \
    -o {INPUT_PARENT_PATH}/asc

In-place predictions#

When trying to convert spectra into another format and place them in the same location as the input spectra, manually copying files is rather tedious. Also, filters that get rid of the file path and only forward the file name, like savitzky-golay, invalidate the use of input-based placeholders like {INPUT_PATH}. For that reason, the set-placeholder plugin can be used to back up such placeholders in other user-defined placeholders. The following pipeline backs up {INPUT_PATH} in the new placeholder {OUTPUT_DIR} and uses that for saving the generated .asc files:

sdc-convert -l INFO \
  from-adams \
    -i "/some/where/*.spec" \
  set-placeholder \
    -l INFO \
    -p OUTPUT_DIR \
    -v "{INPUT_PATH}" \
  savitzky-golay \
  to-asc \
    -l INFO \
    -o "{OUTPUT_DIR}"