Shell: Quick Reference

This post describes the MicroDB shell, which is a Unix-like shell for interacting with MicroDB.

Shell Commands: Quick Reference

show [-t] OID [TAG]              --- show all tags or OID or the chosen tag
tag  [-f] OID TAG VALUE [TYPE]   --- set tag TAG to VALUE on OID (opt. type)
rm   OID [TAG]                   --- remove all or nominated tag(s) from OID
ls   [-l] OID                    --- list tags on an object

help                             --- show the help
pwd                              --- print working database information
whoami                           --- print username
. [-f] FILE                      --- execute commands from FILE
exec [-f] FILE                   --- execute commands from FILE

Here:

• OID is an object identifier. Object identifiers are unicode strings. The empty string is not a valid OID. All other strings are, in principle, valid object identifiers, as long as they do not include the slash character (/). It is recommended that tag names follow the MicroDB tag conventions, but this is not required.
• TAG is the name of a tag (a string).
• VALUE is a tag value, appropriately formatted (see BELOW1).
• TYPE is a type specifier (see BELOW2).
• FILE is an absolute or relative path to a file,.
• Anything in a square brackets indicates something optional.

Types

Tags in MicroDB can contain values, and those values have types.

One of the values a tag can have is the null value null. There is no distinction between a tag whose value is null and a tag without a value.

MicroDB uses both base types, MIME types and special types.

Base Types

The base types stored in MicroDB are:

• null (code n): the null value
• bool (code b): a boolean value, true or false, (synonym: boolean)
• int (code i): an integer value (synonym integer)
• real (code: r): a floating point value (synonym: float)
• str (code: s): a floating point value (synonym: text)
• date (code: D): a date with no time component, always formatted using ISO 8601.
• datetime (code: d): date with a time component, always formatted using ISO 8601, with optional time zones information.

MIME types

MicroDB currently understands a subset of MIME types in addition to base types. This set is likely to expand over time, and it is possible that MicroDB will eventually understand arbitrary MIME types.

Currently supported MIME types are:

• text/html (code H)
• text/xml (code X)
• text/css (code C)
• text/plain (code T)
• application/json (code J)

Special Types

• link (code L) — a hyperlink
• autolink (code a) — an automatic hyperlink
• compound (code c) — a compound type
• template (code t) — a template
• unknown (code unknown) — a value of unknown type.

Automatic Type Inference

When using the tag command, the type of values will be inferred, if not specified explicitly, using common-sense rules.

If tag names are chosen that look like file names with extensions, the extension will be used to infer the type when this is possible. The following tag extensions are used for this inference.

• .html: tag value will be interpreted as text/html
• .xml: tag value will be interpreted as text/xml
• .rss: tag value will be interpreted as text/xml
• .txt: tag value will be interpreted as text/plain
• .json: tag value will be interpreted as application/json
• .D: tag value will be interpreted as a date
• .d: tag value will be interpreted as a datetime
• .c: tag value will be interpreted as compound