> ## Documentation Index
> Fetch the complete documentation index at: https://qi.alphakdb.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Glossary

Below are some of the most commonly used functions and data structures in qi.

## File System

### `.qi.path`

Build paths into `` `:path/to/file``

```q theme={null}
q).qi.path (`data;"HDB";2026.01.01)
`:data/HDB/2026.01.01
```

### `.qi.spath`

Similar to **path** but returns as ` "path/to/file"`

```q theme={null}
q).qi.spath ("data";`WDB;"2026.01.01")
"data/WDB/2026.01.01"
```

### `.qi.ospath`

The same as **spath** on Mac/Linux, different on Windows

```q theme={null}
q).qi.ospath `tp`logs`tp1
"tp\logs\tp1"
```

### `.qi.exists`

Returns a boolean indicating whether a file / folder exists

```q theme={null}
q).qi.exists `:somefile
0b
q).qi.exists (`:data;"hdb";.z.d)    / uses .qi.path
1b
```

### `.qi.ensuredir`

Creates a directory if it does not already exist

```q theme={null}
q).qi.ensuredir "data/wdb/2026.05.01"
```

## Event

### `.event.addhandler`

Register a handler for an event

```q theme={null}
.event.addhandler[`.z.pc;`myportclose]
```

## Cron (timer)

The cron library uses the event library to manage jobs that are to be run on a timer.

### `.cron.add`

Schedule a timer job

```q theme={null}
q).cron.add[`cleanup;.z.p+00:10;01:00]   / run hourly, starting in 10m
```

### `.cron.jobs`

Table of scheduled jobs

### `.cron.start`

If the q timer (`\t`) is 0, set it to `.conf.QTIMER`.

## Inter-process Communication (IPC)

### `.ipc.conn`

Establish / retrieve a connection to a named process

```q theme={null}
q).ipc.conn[`tp1]
8i
q).ipc.conn[`tp1]
8i						/ re-uses if already open

```

### `.ipc.conns`

Table of active connections and their metadata.

## Log

### `error / warn / info / debug / trace`

The log library has various print functions, in the following order of log level:

1. `.log.error`
2. `.log.warn`
3. `.log.info`
4. `.log.debug`
5. `.log.trace`

These functions expect either plain text, or text and a dictionary:

```q theme={null}
q).log.info"testing"
2026.03.13D15:18:34.605564000 info 0 testing
q).log.error ("this is bad";`arg1`arg2!("yes";string .z.d))
2026.03.13D15:19:10.920591000 error 0 yes 2026.03.13 this is bad
```

### `.log.fatal`

Calls `.log.error` before exiting the process.

### `.log.setlevel`

Filters outputs at this level and below e.g.

```q theme={null}
q).log.setlevel`info
```

Now only `error`, `warn`, and `info` messages will appear in the logs.

### `.log.setformat`

Controls the output format of logs. The options are `plain` (default), `logfmt` and `json`.

```q theme={null}
q).log.setformat`plain
q).log.info"this is a test"
2026.03.13D15:22:03.035220000 info 0 this is a test
q).log.setformat`logfmt
q).log.info"this is a test"
ts=2026.03.13D15:22:14.375892000 lvl=info h=0 msg="this is a test"
q).log.setformat`json
q).log.info"this is a test"
{"ts":"2026.03.13D15:22:24.398116000","lvl":"info","h":"0","msg":"this is a test"}
```

### `.log.usefields`

Use custom fields:

```
q).log.setformat`logfmt
q).log.usefields`pid`user`heap!(.z.i;{.z.u};{.Q.w[]`heap})
q).log.info"last test"
ts=2026.03.13D15:24:04.165223000 lvl=info h=0 pid=43047 user=kieran heap=67108864 msg="last test"
```

Fields in `{}` are calculated at log time.