Intro

This is a kdb/q binding for POSIX.2 regular expressions including extended REs and obsolate (legacy) REs. Please refer to regex(7) and regex(3).

The q api is similar to like and it works with enums and mapped types as well.

Examples

q)\l regex.q
q)s where (s:200?`3) rmatch "[a-d][e-h][i-l]|[i-k][e-h][a-d]"
`cfl`iec`kfd`bfk`cfi`cek`cei`kgd`jec
q)n:"(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9]?[0-9])"
q)ip:re"^",n,"\\.",n,"\\.",n,"\\.",n,"$"
q)ip
foreign
q)"192.168.1.999" rmatch ip
0b
q)"192.168.1.100" rmatch ip
1b
q)"192.168.1.100" rmatches ip
"192.168.1.100"
"192"
"168"
,"1"
"100"
q)"192.168.1.100" irmatches ip
0  13
0  3
4  7
8  9
10 13

Build & Install

This repo contains regex.so for Linux but you can also build it with make/gcc.

$ make

Then you can copy regex.so into $QHOME/l64/ or you can copy it into the folder of your q application.

Import

You can load regex.q, that will add the c functons to the .q namespace. If you don't like that, you can add them to the namespace of your liking, eg. to add them to .regex, you can

q).regex:(`:regex 2:`api,1)[];

The rest of this document assumes the .q namespace.

The API

re

Compile a regular expression with

re eregex
re (regex;flags)

where

• eregex is Posix.2 extended RE string
• regex is Posix.2 extended RE or obsolate (legacy) RE string
• flags is a symbol or simbol vector of
  • `ext : if regex is in extended RE format (see REG_EXTENDED)
  • `icase: to ignore case (see REG_ICASE)
  • `nl: to match (^) and ($) after/before new line (see REG_NEWLINE)

The result of the compilation is a 112h type foreign object.

rmatch

Whether text matches a pattern, similar to like

x rmatch y
rmatch[x;y]

where

• x is a symbol (-11h) or string (10h), symbol vector (11h) or list of strings or a dictionary with them as values
• y is a compiled regex or the argment to function re

rmatches

Subexpression matches

x rmatches y
rmatches[x;y]

where

• x is a symbol (-11h) or string (10h)
• y is a compiled regex or the argment to function re

Returns at most 256 substrings of x starting with the matching substring and followed by up to 255 subexpression matches.

irmatches

Same as rmatches except it returns a list of (start;end+1) positions of the matching substring and subexpression matches.