OpenSearch/docs/reference/eql/functions.asciidoc

[[eql-function-ref]]
== EQL function reference
++++
<titleabbrev>Function reference</titleabbrev>
++++

experimental::[]

{es} supports the following EQL functions:

* <<eql-fn-add>>
* <<eql-fn-between>>
* <<eql-fn-cidrmatch>>
* <<eql-fn-concat>>
* <<eql-fn-divide>>
* <<eql-fn-endswith>>
* <<eql-fn-indexof>>
* <<eql-fn-length>>
* <<eql-fn-match>>
* <<eql-fn-modulo>>
* <<eql-fn-multiply>>
* <<eql-fn-startswith>>
* <<eql-fn-string>>
* <<eql-fn-stringcontains>>
* <<eql-fn-substring>>
* <<eql-fn-subtract>>
* <<eql-fn-wildcard>>

[discrete]
[[eql-fn-add]]
=== `add`
Returns the sum of two provided addends.

[%collapsible]
====
*Example*
[source,eql]
----
add(4, 5)                                           // returns 9
add(4, 0.5)                                         // returns 4.5
add(0.5, 0.25)                                      // returns 0.75
add(4, -2)                                          // returns 2
add(-2, -2)                                         // returns -4

// process.args_count = 4
add(process.args_count, 5)                          // returns 9
add(process.args_count, 0.5)                        // returns 4.5

// process.parent.args_count = 2
add(process.args_count, process.parent.args_count)  // returns 6

// null handling
add(null, 4)                                        // returns null
add(4. null)                                        // returns null
add(null, process.args_count)                       // returns null
add(process.args_count null)                        // returns null
----

*Syntax*
[source,txt]
----
add(<addend>, <addend>)
----

*Parameters:*

`<addend>`::
(Required, integer or float or `null`)
Addend to add. If `null`, the function returns `null`.
+
Two addends are required. No more than two addends can be provided.
+
If using a field as the argument, this parameter supports only
<<number,`numeric`>> field datatypes.

*Returns:* integer, float, or `null`
====

[discrete]
[[eql-fn-between]]
=== `between`

Extracts a substring that's between a provided `left` and `right` text in a
source string.

[%collapsible]
====
*Example*
[source,eql]
----
// file.path = "C:\\Windows\\System32\\cmd.exe"
between(file.path, "system32\\\\", ".exe")   // returns "cmd"
between(file.path, "workspace\\\\", ".exe")  // returns ""


// Greedy matching defaults to false.
between(file.path, "\\\\", "\\\\", false)  // returns "Windows"
// Sets greedy matching to true
between(file.path, "\\\\", "\\\\", true)  // returns "Windows\\System32"

// Case sensitivity defaults to false.
between(file.path, "system32\\\\", ".exe", false, false)  // returns "cmd"
// Sets case sensitivity to true
between(file.path, "system32\\\\", ".exe", false, true)   // returns ""
between(file.path, "System32\\\\", ".exe", false, true)   // returns "cmd"

// empty source string
between("", "system32\\\\", ".exe")          // returns ""
between("", "", "")                          // returns ""

// null handling
between(null, "system32\\\\", ".exe")                   // returns null
----

*Syntax*
[source,txt]
----
between(<source>, <left>, <right>[, <greedy_matching>, <case_sensitive>])
----

*Parameters*

`<source>`::
+
--
(Required, string or `null`)
Source string. Empty strings return an empty string (`""`), regardless of the
`<left>` or `<right>` parameters. If `null`, the function returns `null`.

If using a field as the argument, this parameter supports only the following
field datatypes:

* <<keyword,`keyword`>>
* <<constant-keyword,`constant_keyword`>>
* <<text,`text`>> field with a <<keyword,`keyword`>> or
  <<constant-keyword,`constant_keyword`>> sub-field

Fields containing <<array,array values>> use the first array item only.
--

`<left>`::
+
--
(Required, string)
Text to the left of the substring to extract. This text should include
whitespace.

If using a field as the argument, this parameter supports only the following
field datatypes:

* <<keyword,`keyword`>>
* <<constant-keyword,`constant_keyword`>>
* <<text,`text`>> field with a <<keyword,`keyword`>> or
  <<constant-keyword,`constant_keyword`>> sub-field

<<array,Array values>> are not supported.
--

`<right>`::
+
--
(Required, string)
Text to the right of the substring to extract. This text should include
whitespace.

If using a field as the argument, this parameter supports only the following
field datatypes:

* <<keyword,`keyword`>>
* <<constant-keyword,`constant_keyword`>>
* <<text,`text`>> field with a <<keyword,`keyword`>> or
  <<constant-keyword,`constant_keyword`>> sub-field

<<array,Array values>> are not supported.
--

`<greedy_matching>`::
(Optional, boolean)
If `true`, match the longest possible substring, similar to `.*` in regular
expressions. If `false`, match the shortest possible substring, similar to `.*?`
in regular expressions. Defaults to `false`.

`<case_sensitive>`::
(Optional, boolean)
If `true`, matching is case-sensitive. Defaults to `false`.

*Returns:* string or `null`
====

[discrete]
[[eql-fn-cidrmatch]]
=== `cidrMatch`

Returns `true` if an IP address is contained in one or more provided
https://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing[CIDR] blocks.

[%collapsible]
====
*Example*

[source,eql]
----
// source.address = "192.168.152.12"
cidrMatch(source.address, "192.168.0.0/16")               // returns true
cidrMatch(source.address, "192.168.0.0/16", "10.0.0.0/8") // returns true
cidrMatch(source.address, "10.0.0.0/8")                   // returns false
cidrMatch(source.address, "10.0.0.0/8", "10.128.0.0/9")   // returns false

// null handling
cidrMatch(null, "10.0.0.0/8")                             // returns null
cidrMatch(source.address, null)                           // returns null
----

*Syntax*
[source,txt]
----
`cidrMatch(<ip_address>, <cidr_block>[, ...])`
----

*Parameters*

`<ip_address>`::
(Required, string or `null`)
IP address. Supports
https://en.wikipedia.org/wiki/IPv4[IPv4] and
https://en.wikipedia.org/wiki/IPv6[IPv6] addresses. If `null`, the function
returns `null`.
+
If using a field as the argument, this parameter supports only the <<ip,`ip`>>
field datatype.

`<cidr_block>`::
(Required{multi-arg}, string or `null`)
CIDR block you wish to search. If `null`, the function returns `null`.

*Returns:* boolean or `null`
====

[discrete]
[[eql-fn-concat]]
=== `concat`

Returns a concatenated string of provided values.

[%collapsible]
====
*Example*
[source,eql]
----
concat("process is ", "regsvr32.exe")         // returns "process is regsvr32.exe"
concat("regsvr32.exe", " ", 42)               // returns "regsvr32.exe 42"
concat("regsvr32.exe", " ", 42.5)             // returns "regsvr32.exe 42.5"
concat("regsvr32.exe", " ", true)             // returns "regsvr32.exe true"
concat("regsvr32.exe")                        // returns "regsvr32.exe"

// process.name = "regsvr32.exe"
concat(process.name, " ", 42)                 // returns "regsvr32.exe 42"
concat(process.name, " ", 42.5)               // returns "regsvr32.exe 42.5"
concat("process is ", process.name)           // returns "process is regsvr32.exe"
concat(process.name, " ", true)               // returns "regsvr32.exe true"
concat(process.name)                          // returns "regsvr32.exe"

// process.arg_count = 4
concat(process.name, " ", process.arg_count)  // returns "regsvr32.exe 4"

// null handling
concat(null, "regsvr32.exe")                  // returns null
concat(process.name, null)                    // returns null
concat(null)                                  // returns null 
----

*Syntax*
[source,txt]
----
concat(<value>[, <value>])
----

*Parameters*

`<value>`::
(Required{multi-arg-ref})
Value to concatenate. If any of the arguments are `null`, the function returns `null`.
+
If using a field as the argument, this parameter does not support the
<<text,`text`>> field datatype.

*Returns:* string or `null`
====

[discrete]
[[eql-fn-divide]]
==== `divide`
Returns the quotient of a provided dividend and divisor.

[%collapsible]
====

[[eql-divide-fn-float-rounding]]
[WARNING]
=====
If both the dividend and divisor are integers, the `divide` function _rounds
down_ any returned floating point numbers to the nearest integer.

EQL queries in {es} should account for this rounding. To avoid rounding, convert
either the dividend or divisor to a float.

[%collapsible]
.**Example**
======
The `process.args_count` field is a <<number,`long`>> integer field containing a
count of process arguments.

A user might expect the following EQL query to only match events with a
`process.args_count` value of `4`.

[source,eql]
----
process where divide(4, process.args_count) == 1
----

However, the EQL query matches events with a `process.args_count` value of `3`
or `4`.

For events with a `process.args_count` value of `3`, the `divide` function
returns a floating point number of `1.333...`, which is rounded down to `1`.

To match only events with a `process.args_count` value of `4`, convert
either the dividend or divisor to a float.

The following EQL query changes the integer `4` to the equivalent float `4.0`.

[source,eql]
----
process where divide(4.0, process.args_count) == 1
----
======
=====

*Example*
[source,eql]
----
divide(4, 2)                                            // returns 2
divide(4, 3)                                            // returns 1
divide(4, 3.0)                                          // returns 1.333...
divide(4, 0.5)                                          // returns 8
divide(0.5, 4)                                          // returns 0.125
divide(0.5, 0.25)                                       // returns 2.0
divide(4, -2)                                           // returns -2
divide(-4, -2)                                          // returns 2

// process.args_count = 4
divide(process.args_count, 2)                           // returns 2
divide(process.args_count, 3)                           // returns 1
divide(process.args_count, 3.0)                         // returns 1.333...
divide(12, process.args_count)                          // returns 3
divide(process.args_count, 0.5)                         // returns 8
divide(0.5, process.args_count)                         // returns 0.125

// process.parent.args_count = 2
divide(process.args_count, process.parent.args_count)   // returns 2

// null handling
divide(null, 4)                                         // returns null
divide(4, null)                                         // returns null
divide(null, process.args_count)                        // returns null
divide(process.args_count, null)                        // returns null
----

*Syntax*
[source,txt]
----
divide(<dividend>, <divisor>)
----

*Parameters*

`<dividend>`::
(Required, integer or float or `null`)
Dividend to divide. If `null`, the function returns `null`.
+
If using a field as the argument, this parameter supports only
<<number,`numeric`>> field datatypes.

`<divisor>`::
(Required, integer or float or `null`)
Divisor to divide by. If `null`, the function returns `null`. This value cannot
be zero (`0`).
+
If using a field as the argument, this parameter supports only
<<number,`numeric`>> field datatypes.

*Returns:* integer, float, or null
====

[discrete]
[[eql-fn-endswith]]
=== `endsWith`

Returns `true` if a source string ends with a provided substring.

[%collapsible]
====
*Example*
[source,eql]
----
endsWith("regsvr32.exe", ".exe")          // returns true
endsWith("regsvr32.exe", ".dll")          // returns false
endsWith("", "")                          // returns true

// file.name = "regsvr32.exe"
endsWith(file.name, ".exe")               // returns true
endsWith(file.name, ".dll")               // returns false

// file.extension = ".exe"
endsWith("regsvr32.exe", file.extension)  // returns true
endsWith("ntdll.dll", file.name)          // returns false

// file.name = [ "ntdll.dll", "regsvr32.exe" ]
endsWith(file.name, ".dll")               // returns true
endsWith(file.name, ".exe")               // returns false

// null handling
endsWith("regsvr32.exe", null)            // returns null
endsWith("", null)                        // returns null
endsWith(null, ".exe")                    // returns null
endsWith(null, null)                      // returns null
----

*Syntax*
[source,txt]
----
endsWith(<source>, <substring>)
----

*Parameters*

`<source>`::
+
--
(Required, string or `null`)
Source string. If `null`, the function returns `null`.

If using a field as the argument, this parameter supports only the following
field datatypes:

* <<keyword,`keyword`>>
* <<constant-keyword,`constant_keyword`>>
* <<text,`text`>> field with a <<keyword,`keyword`>> or
  <<constant-keyword,`constant_keyword`>> sub-field

Fields containing <<array,array values>> use the first array item only.
--

`<substring>`::
+
--
(Required, string or `null`)
Substring to search for. If `null`, the function returns `null`.

If using a field as the argument, this parameter supports only the following
field datatypes:

* <<keyword,`keyword`>>
* <<constant-keyword,`constant_keyword`>>
* <<text,`text`>> field with a <<keyword,`keyword`>> or
  <<constant-keyword,`constant_keyword`>> sub-field
--

*Returns:* boolean or `null`
====

[discrete]
[[eql-fn-indexof]]
=== `indexOf`

Returns the first position of a provided substring in a source string.

If an optional start position is provided, this function returns the first
occurrence of the substring at or after the start position.

[%collapsible]
====
*Example*
[source,eql]
----
// url.domain = "subdomain.example.com"
indexOf(url.domain, ".")        // returns 9
indexOf(url.domain, ".", 9)     // returns 9
indexOf(url.domain, ".", 10)    // returns 17
indexOf(url.domain, ".", -6)    // returns 9

// empty strings
indexOf("", "")                 // returns 0
indexOf(url.domain, "")         // returns 0
indexOf(url.domain, "", 9)      // returns 9
indexOf(url.domain, "", 10)     // returns 10
indexOf(url.domain, "", -6)     // returns 0

// missing substrings
indexOf(url.domain, "z")        // returns null
indexOf(url.domain, "z", 9)     // returns null

// start position is higher than string length
indexOf(url.domain, ".", 30)    // returns null

// null handling
indexOf(null, ".", 9)           // returns null
indexOf(url.domain, null, 9)    // returns null
indexOf(url.domain, ".", null)  // returns null
----

*Syntax*
[source,txt]
----
indexOf(<source>, <substring>[, <start_pos>])
----

*Parameters*

`<source>`::
+
--
(Required, string or `null`)
Source string. If `null`, the function returns `null`.

If using a field as the argument, this parameter supports only the following
field datatypes:

* <<keyword,`keyword`>>
* <<constant-keyword,`constant_keyword`>>
* <<text,`text`>> field with a <<keyword,`keyword`>> or
  <<constant-keyword,`constant_keyword`>> sub-field
--

`<substring>`::
+
--
(Required, string or `null`)
Substring to search for.

If this argument is `null` or the `<source>` string does not contain this
substring, the function returns `null`.

If the `<start_pos>` is positive, empty strings (`""`) return the `<start_pos>`.
Otherwise, empty strings return `0`.

If using a field as the argument, this parameter supports only the following
field datatypes:

* <<keyword,`keyword`>>
* <<constant-keyword,`constant_keyword`>>
* <<text,`text`>> field with a <<keyword,`keyword`>> or
  <<constant-keyword,`constant_keyword`>> sub-field
--

`<start_pos>`::
+
--
(Optional, integer or `null`)
Starting position for matching. The function will not return positions before
this one. Defaults to `0`.

Positions are zero-indexed. Negative offsets are treated as `0`.

If this argument is `null` or higher than the length of the `<source>` string,
the function returns `null`.

If using a field as the argument, this parameter supports only the following
<<number,numeric>> field datatypes:

* `long`
* `integer`
* `short`
* `byte`
--

*Returns:* integer or `null`
====

[discrete]
[[eql-fn-length]]
=== `length`

Returns the character length of a provided string, including whitespace and
punctuation.

[%collapsible]
====
*Example*
[source,eql]
----
length("explorer.exe")         // returns 12
length("start explorer.exe")   // returns 18
length("")                     // returns 0
length(null)                   // returns null

// process.name = "regsvr32.exe"
length(process.name)           // returns 12
----

*Syntax*
[source,txt]
----
length(<string>)
----

*Parameters*

`<string>`::
+
--
(Required, string or `null`)
String for which to return the character length. If `null`, the function returns
`null`. Empty strings return `0`.

If using a field as the argument, this parameter supports only the following
field datatypes:

* <<keyword,`keyword`>>
* <<constant-keyword,`constant_keyword`>>
* <<text,`text`>> field with a <<keyword,`keyword`>> or
  <<constant-keyword,`constant_keyword`>> sub-field

<<array,Array values>> are not supported.
--

*Returns:* integer or `null`
====

[discrete]
[[eql-fn-match]]
=== `match`

Returns `true` if a source string matches one or more provided regular
expressions.

[%collapsible]
====
*Example*
[source,eql]
----
match("explorer.exe", "[a-z]*?.exe")           // returns true
match("explorer.exe", "[a-z]*?.exe", "[1-9]")  // returns true
match("explorer.exe", "[1-9]")                 // returns false
match("explorer.exe", "")                      // returns false

// process.name = "explorer.exe"
match(process.name, "[a-z]*?.exe")             // returns true
match(process.name, "[a-z]*?.exe", "[1-9]")    // returns true
match(process.name, "[1-9]")                   // returns false
match(process.name, "")                        // returns false

// null handling
match(null, "[a-z]*?.exe")                     // returns null
----

*Syntax*
[source,txt]
----
match(<source>, <reg_exp>[, ...])
----

*Parameters*

`<source>`::
+
--
(Required, string or `null`)
Source string. If `null`, the function returns `null`.

If using a field as the argument, this parameter supports only the following
field datatypes:

* <<keyword,`keyword`>>
* <<constant-keyword,`constant_keyword`>>
* <<text,`text`>> field with a <<keyword,`keyword`>> or
  <<constant-keyword,`constant_keyword`>> sub-field
--

`<reg_exp>`::
+
--
(Required{multi-arg-ref}, string)
Regular expression used to match the source string. For supported syntax, see
<<regexp-syntax>>.
https://docs.oracle.com/javase/tutorial/essential/regex/pre_char_classes.html[Predefined
character classes] are not supported.

Fields are not supported as arguments.
--

*Returns:* boolean or `null`
====

[discrete]
[[eql-fn-modulo]]
=== `modulo`
Returns the remainder of the division of a provided dividend and divisor.

[%collapsible]
====
*Example*
[source,eql]
----
modulo(10, 6)                                       // returns 4
modulo(10, 5)                                       // returns 0
modulo(10, 0.5)                                     // returns 0
modulo(10, -6)                                      // returns 4
modulo(-10, -6)                                     // returns -4

// process.args_count = 10
modulo(process.args_count, 6)                       // returns 4
modulo(process.args_count, 5)                       // returns 0
modulo(106, process.args_count)                     // returns 6
modulo(process.args_count, -6)                      // returns 4
modulo(process.args_count, 0.5)                     // returns 0

// process.parent.args_count = 6
add(process.args_count, process.parent.args_count)  // returns 4

// null handling
modulo(null, 5)                                     // returns null
modulo(7, null)                                     // returns null
modulo(null, process.args_count)                    // returns null
modulo(process.args_count, null)                    // returns null
----

*Syntax*
[source,txt]
----
modulo(<dividend>, <divisor>)
----

*Parameters*

`<dividend>`::
(Required, integer or float or `null`)
Dividend to divide. If `null`, the function returns `null`. Floating point
numbers return `0`.
+
If using a field as the argument, this parameter supports only
<<number,`numeric`>> field datatypes.

`<divisor>`::
(Required, integer or float or `null`)
Divisor to divide by. If `null`, the function returns `null`. Floating point
numbers return `0`. This value cannot be zero (`0`).
+
If using a field as the argument, this parameter supports only
<<number,`numeric`>> field datatypes.

*Returns:* integer, float, or `null`
====

[discrete]
[[eql-fn-multiply]]
=== `multiply`

Returns the product of two provided factors.

[%collapsible]
====
*Example*
[source,eql]
----
multiply(2, 2)                                           // returns 4
multiply(0.5, 2)                                         // returns 1
multiply(0.25, 2)                                        // returns 0.5
multiply(-2, 2)                                          // returns -4
multiply(-2, -2)                                         // returns 4

// process.args_count = 2
multiply(process.args_count, 2)                          // returns 4
multiply(0.5, process.args_count)                        // returns 1
multiply(0.25, process.args_count)                       // returns 0.5

// process.parent.args_count = 3
multiply(process.args_count, process.parent.args_count)  // returns 6

// null handling
multiply(null, 2)                                        // returns null
multiply(2, null)                                        // returns null
----

*Syntax*
[source,txt]
----
multiply(<factor, <factor>)
----

*Parameters*

`<factor>`::
+
--
(Required, integer or float or `null`)
Factor to multiply.  If `null`, the function returns `null`.

Two factors are required. No more than two factors can be provided.

If using a field as the argument, this parameter supports only
<<number,`numeric`>> field datatypes.
--

*Returns:* integer, float, or `null`
====

[discrete]
[[eql-fn-startswith]]
=== `startsWith`

Returns `true` if a source string begins with a provided substring.

[%collapsible]
====
*Example*
[source,eql]
----
startsWith("regsvr32.exe", "regsvr32")  // returns true
startsWith("regsvr32.exe", "explorer")  // returns false
startsWith("", "")                      // returns true

// process.name = "regsvr32.exe"
startsWith(process.name, "regsvr32")    // returns true
startsWith(process.name, "explorer")    // returns false

// process.name = "regsvr32"
startsWith("regsvr32.exe", process.name) // returns true
startsWith("explorer.exe", process.name) // returns false

// process.name = [ "explorer.exe", "regsvr32.exe" ]
startsWith(process.name, "explorer")    // returns true
startsWith(process.name, "regsvr32")    // returns false

// null handling
startsWith("regsvr32.exe", null)        // returns null
startsWith("", null)                    // returns null
startsWith(null, "regsvr32")            // returns null
startsWith(null, null)                  // returns null
----

*Syntax*
[source,txt]
----
startsWith(<source>, <substring>)
----

*Parameters*

`<source>`::
+
--
(Required, string or `null`)
Source string. If `null`, the function returns `null`.

If using a field as the argument, this parameter supports only the following
field datatypes:

* <<keyword,`keyword`>>
* <<constant-keyword,`constant_keyword`>>
* <<text,`text`>> field with a <<keyword,`keyword`>> or
  <<constant-keyword,`constant_keyword`>> sub-field

Fields containing <<array,array values>> use the first array item only.
--

`<substring>`::
+
--
(Required, string or `null`)
Substring to search for. If `null`, the function returns `null`.

If using a field as the argument, this parameter supports only the following
field datatypes:

* <<keyword,`keyword`>>
* <<constant-keyword,`constant_keyword`>>
* <<text,`text`>> field with a <<keyword,`keyword`>> or
  <<constant-keyword,`constant_keyword`>> sub-field
--

*Returns:* boolean or `null`
====

[discrete]
[[eql-fn-string]]
=== `string`

Converts a value to a string.

[%collapsible]
====
*Example*
[source,eql]
----
string(42)               // returns "42"
string(42.5)             // returns "42.5"
string("regsvr32.exe")   // returns "regsvr32.exe"
string(true)             // returns "true"

// null handling
string(null)             // returns null
----

*Syntax*
[source,txt]
----
string(<value>)
----

*Parameters*

`<value>`::
(Required)
Value to convert to a string. If `null`, the function returns `null`.
+
If using a field as the argument, this parameter does not support the
<<text,`text`>> field datatype.

*Returns:* string or `null`
====

[discrete]
[[eql-fn-stringcontains]]
=== `stringContains`

Returns `true` if a source string contains a provided substring.

[%collapsible]
====
*Example*
[source,eql]
----
// process.command_line = "start regsvr32.exe"
stringContains(process.command_line, "regsvr32")  // returns true
stringContains(process.command_line, "start ")    // returns true
stringContains(process.command_line, "explorer")  // returns false

// process.name = "regsvr32.exe"
stringContains(command_line, process.name)        // returns true

// empty strings
stringContains("", "")                            // returns false
stringContains(process.command_line, "")          // returns false

// null handling
stringContains(null, "regsvr32")                  // returns null
stringContains(process.command_line, null)        // returns null
----

*Syntax*
[source,txt]
----
stringContains(<source>, <substring>)
----

*Parameters*

`<source>`::
(Required, string or `null`)
Source string to search. If `null`, the function returns `null`.

If using a field as the argument, this parameter supports only the following
field datatypes:

* <<keyword,`keyword`>>
* <<constant-keyword,`constant_keyword`>>
* <<text,`text`>> field with a <<keyword,`keyword`>> or
  <<constant-keyword,`constant_keyword`>> sub-field

`<substring>`::
(Required, string or `null`)
Substring to search for. If `null`, the function returns `null`.

If using a field as the argument, this parameter supports only the following
field datatypes:

* <<keyword,`keyword`>>
* <<constant-keyword,`constant_keyword`>>
* <<text,`text`>> field with a <<keyword,`keyword`>> or
  <<constant-keyword,`constant_keyword`>> sub-field

*Returns:* boolean or `null`
====

[discrete]
[[eql-fn-substring]]
=== `substring`

Extracts a substring from a source string at provided start and end positions.

If no end position is provided, the function extracts the remaining string.

[%collapsible]
====
*Example*
[source,eql]
----
substring("start regsvr32.exe", 6)        // returns "regsvr32.exe"
substring("start regsvr32.exe", 0, 5)     // returns "start"
substring("start regsvr32.exe", 6, 14)    // returns "regsvr32"
substring("start regsvr32.exe", -4)       // returns ".exe"
substring("start regsvr32.exe", -4, -1)   // returns ".ex"
----

*Syntax*
[source,txt]
----
substring(<source>, <start_pos>[, <end_pos>])
----

*Parameters*

`<source>`::
(Required, string)
Source string.

`<start_pos>`::
+
--
(Required, integer)
Starting position for extraction.

If this position is higher than the `<end_pos>` position or the length of the
`<source>` string, the function returns an empty string.

Positions are zero-indexed. Negative offsets are supported.
--

`<end_pos>`::
(Optional, integer)
Exclusive end position for extraction. If this position is not provided, the
function returns the remaining string.
+
Positions are zero-indexed. Negative offsets are supported.

*Returns:* string
====

[discrete]
[[eql-fn-subtract]]
=== `subtract`
Returns the difference between a provided minuend and subtrahend.

[%collapsible]
====
*Example*
[source,eql]
----
subtract(10, 2)                                          // returns 8
subtract(10.5, 0.5)                                      // returns 10
subtract(1, 0.2)                                         // returns 0.8
subtract(-2, 4)                                          // returns -8
subtract(-2, -4)                                         // returns 8

// process.args_count = 10
subtract(process.args_count, 6)                          // returns 4
subtract(process.args_count, 5)                          // returns 5
subtract(15, process.args_count)                         // returns 5
subtract(process.args_count, 0.5)                        // returns 9.5

// process.parent.args_count = 6
subtract(process.args_count, process.parent.args_count)  // returns 4

// null handling
subtract(null, 2)                                        // returns null
subtract(2, null)                                        // returns null
----

*Syntax*
[source,txt]
----
subtract(<minuend>, <subtrahend>)
----

*Parameters*

`<minuend>`::
(Required, integer or float or `null`)
Minuend to subtract from.
+
If using a field as the argument, this parameter supports only
<<number,`numeric`>> field datatypes.

`<subtrahend>`::
(Optional, integer or float or `null`)
Subtrahend to subtract. If `null`, the function returns `null`.
+
If using a field as the argument, this parameter supports only
<<number,`numeric`>> field datatypes.

*Returns:* integer, float, or `null`
====

[discrete]
[[eql-fn-wildcard]]
=== `wildcard`

Returns `true` if a source string matches one or more provided wildcard
expressions.

[%collapsible]
====
*Example*
[source,eql]
----
// The two following expressions are equivalent.
process.name == "*regsvr32*" or process.name == "*explorer*"
wildcard(process.name, "*regsvr32*", "*explorer*")

// process.name = "regsvr32.exe"
wildcard(process.name, "*regsvr32*")                // returns true
wildcard(process.name, "*regsvr32*", "*explorer*")  // returns true
wildcard(process.name, "*explorer*")                // returns false
wildcard(process.name, "*explorer*", "*scrobj*")    // returns false

// empty strings
wildcard("", "*start*")                             // returns false
wildcard("", "*")                                   // returns true
wildcard("", "")                                    // returns true

// null handling
wildcard(null, "*regsvr32*")                        // returns null
wildcard(process.name, null)                        // returns null
----

*Syntax*
[source,txt]
----
wildcard(<source>, <wildcard_exp>[, ...])
----

*Parameters*

`<source>`::
+
--
(Required, string)
Source string. If `null`, the function returns `null`.

If using a field as the argument, this parameter supports only the following
field datatypes:

* <<keyword,`keyword`>>
* <<constant-keyword,`constant_keyword`>>
* <<text,`text`>> field with a <<keyword,`keyword`>> or
  <<constant-keyword,`constant_keyword`>> sub-field
--

`<wildcard_exp>`::
+
--
(Required{multi-arg-ref}, string)
Wildcard expression used to match the source string. If `null`, the function
returns `null`. Fields are not supported as arguments.
--

*Returns:* boolean
====