pferd/CONFIG.md

Config file format

A config file consists of sections. A section begins with a [section] header, which is followed by a list of key = value or key: value pairs. Comments must be on their own line and start with # or ;. Multiline values must be indented beyond their key. For more details and some examples on the format, see the configparser documentation (basic interpolation is enabled).

The DEFAULT section

This section contains global configuration values. It can also be used to set default values for the other sections.

• working_dir: The directory PFERD operates in. Set to an absolute path to make PFERD operate the same regardless of where it is executed. All other paths in the config file are interpreted relative to this path. If this path is relative, it is interpreted relative to the script's working dir. ~ is expanded to the current user's home directory. (Default: .)

The crawl:* sections

Sections whose names start with crawl: are used to configure crawlers. The rest of the section name specifies the name of the crawler.

A crawler synchronizes a remote resource to a local directory. There are different types of crawlers for different kinds of resources, e. g. ILIAS courses or lecture websites.

Each crawl section represents an instance of a specific type of crawler. The type option is used to specify the crawler type. The crawler's name is usually used as the name for the output directory. New crawlers can be created simply by adding a new crawl section to the config file.

Depending on a crawler's type, it may have different options. For more details, see the type's documentation below. The following options are common to all crawlers:

• type: The types are specified in this section.
• output_dir: The directory the crawler synchronizes files to. A crawler will never place any files outside of this directory. (Default: crawler's name)
• redownload: When to download again a file that is already present locally. (Default: never-smart)
  • never: If a file is present locally, it is not downloaded again.
  • never-smart: Like never, but PFERD tries to detect if an already downloaded files has changed via some (unreliable) heuristics.
  • always: All files are always downloaded, regardless of whether they are already present locally.
  • always-smart: Like always, but PFERD tries to avoid unnecessary downloads via some (unreliable) heuristics.
• on_conflict: What to do when the local and remote versions of a file or directory differ. Includes the cases where a file is replaced by a directory or a directory by a file. (Default: prompt)
  • prompt: Always ask the user before overwriting or deleting local files and directories.
  • local-first: Always keep the local file or directory. Equivalent to using prompt and always choosing "no". Implies that redownload is set to never.
  • remote-first: Always keep the remote file or directory. Equivalent to using prompt and always choosing "yes".
  • no-delete: Never delete local files, but overwrite local files if the remote file is different.
• transform: Rules for renaming and excluding certain files and directories. For more details, see this section. (Default: empty)

Some crawlers may also require credentials for authentication. To configure how the crawler obtains its credentials, the auth option is used. It is set to the full name of an auth section (including the auth: prefix).

Here is a simple example:

[auth:example]
type = simple
username = foo
password = bar

[crawl:something]
type = some-complex-crawler
auth = auth:example

The auth:* sections

Sections whose names start with auth: are used to configure authenticators. An authenticator provides login credentials to one or more crawlers.

Authenticators work similar to crawlers: A section represents an authenticator instance, whose name is the rest of the section name. The type is specified by the type option.

Depending on an authenticator's type, it may have different options. For more details, see the type's documentation below. The only option common to all authenticators is type:

• type: The types are specified in this section.

Crawler types

The local crawler

This crawler crawls a local directory. It is really simple and mostly useful for testing different setups. The various delay options are meant to make the crawler simulate a slower, network-based crawler.

• path: Path to the local directory to crawl. (Required)
• crawl_delay: Maximum artificial delay (in seconds) to simulate for crawl requests. (Optional)
• download_delay: Maximum artificial delay (in seconds) to simulate for download requests. (Optional)
• download_speed: Download speed (in bytes per second) to simulate. (Optional)

Authenticator types

The simple authenticator

With this authenticator, the username and password can be set directly in the config file. If the username or password are not specified, the user is prompted via the terminal.

• username: The username. (Optional)
• password: The password. (Optional)

Transformation rules

Transformation rules are rules for renaming and excluding files and directories. They are specified line-by-line in a crawler's transform option. When a crawler needs to apply a rule to a path, it goes through this list top-to-bottom and choose the first matching rule.

Each line has the format SOURCE ARROW TARGET where TARGET is optional. SOURCE is either a normal path without spaces (e. g. foo/bar), or a string literal delimited by " or ' (e. g. "foo\" bar/baz"). Python's string escape syntax is supported. Trailing slashes are ignored. TARGET can be formatted like SOURCE, but it can also be a single exclamation mark without quotes (!). ARROW is one of -->, -exact-> and -re->.

If a rule's target is !, this means that when the rule matches on a path, the corresponding file or directory is ignored. If a rule's target is missing, the path is matched but not modified.

The --> arrow

The --> arrow is a basic renaming operation. If a path begins with SOURCE, that part of the path is replaced with TARGET. This means that the rule foo/bar --> baz would convert foo/bar into baz, but also foo/bar/xyz into baz/xyz. The rule foo --> ! would ignore a directory named foo as well as all its contents.

The -exact-> arrow

The -exact-> arrow requires the path to match SOURCE exactly. This means that the rule foo/bar -exact-> baz would still convert foo/bar into baz, but foo/bar/xyz would be unaffected. Also, foo -exact-> ! would only ignore foo, but not its contents (if it has any). The examples below show why this is useful.

The -re-> arrow

The -re-> arrow uses regular expressions. SOURCE is a regular expression that must match the entire path. If this is the case, then the capturing groups are available in TARGET for formatting.

TARGET uses Python's format string syntax. The n-th capturing group can be referred to as {g<n>} (e. g. {g3}). {g0} refers to the original path. If capturing group n's contents are a valid integer, the integer value is available as {i<n>} (e. g. {i3}). If capturing group n's contents are a valid float, the float value is available as {f<n>} (e. g. {f3}).

Python's format string syntax has rich options for formatting its arguments. For example, to left-pad the capturing group 3 with the digit 0 to width 5, you can use {i3:05}.

PFERD even allows you to write entire expressions inside the curly braces, for example {g2.lower()} or {g3.replace(' ', '_')}.

Example: Tutorials

You have an ILIAS course with lots of tutorials, but are only interested in a single one?

tutorials/
  |- tut_01/
  |- tut_02/
  |- tut_03/
  ...

You can use a mix of normal and exact arrows to get rid of the other ones and move the tutorials/tut_02/ folder to my_tut/:

tutorials/tut_02 --> my_tut
tutorials -exact->
tutorials --> !

The second rule is required for many crawlers since they use the rules to decide which directories to crawl. If it was missing when the crawler looks at tutorials/, the third rule would match. This means the crawler would not crawl the tutorials/ directory and thus not discover that tutorials/tut02/ existed.

Since the second rule is only relevant for crawling, the TARGET is left out.

Example: Lecture slides

You have a course with slides like Lecture 3: Linear functions.PDF and you would like to rename them to 03_linear_functions.pdf.

Lectures/
  |- Lecture 1: Introduction.PDF
  |- Lecture 2: Vectors and matrices.PDF
  |- Lecture 3: Linear functions.PDF
  ...

To do this, you can use the most powerful of arrows: The regex arrow.

"Lectures/Lecture (\\d+): (.*)\\.PDF" -re-> "Lectures/{i1:02}_{g2.lower().replace(' ', '_')}.pdf"

Note the escaped backslashes on the SOURCE side.