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

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File System

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.qi.path

Build paths into `:path/to/file 
q).qi.path (`data;"HDB";2026.01.01)
`:data/HDB/2026.01.01

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.qi.spath

Similar to path but returns as "path/to/file" 
q).qi.spath ("data";`WDB;"2026.01.01")
"data/WDB/2026.01.01"

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.qi.ospath

The same as spath on Mac/Linux, different on Windows 
q).qi.ospath `tp`logs`tp1
"tp\logs\tp1"

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.qi.exists

Returns a boolean indicating whether a file / folder exists 
q).qi.exists `:somefile
0b
q).qi.exists (`:data;"hdb";.z.d)    / uses .qi.path
1b

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.qi.ensuredir

Creates a directory if it does not already exist 
q).qi.ensuredir "data/wdb/2026.05.01"

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Event

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.event.addhandler

Register a handler for an event 
.event.addhandler[`.z.pc;`myportclose]

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Cron (timer)

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

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.cron.add

Schedule a timer job 
q).cron.add[`cleanup;.z.p+00:10;01:00]   / run hourly, starting in 10m

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.cron.jobs

Table of scheduled jobs

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.cron.start

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

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Inter-process Communication (IPC)

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.ipc.conn

Establish / retrieve a connection to a named process 
q).ipc.conn[`tp1]
8i
q).ipc.conn[`tp1]
8i						/ re-uses if already open

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.ipc.ping

Sends a command asynchronously to a process, but closes the connection immediately afterwards. Useful for versions of kdb+ that have connection limits 
q).ipc.ping[`tp1;(`somefunc;10 20 30)]

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.ipc.conns

Table of active connections and their metadata.

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Log

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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).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

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.log.fatal

Calls .log.error before exiting the process.

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.log.setlevel

Filters outputs at this level and below e.g. 
q).log.setlevel`info
Now only error, warn, and info messages will appear in the logs.

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.log.setformat

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

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.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.