RExtract

The RExtract function uses regular expressions to extract a substring from a string.

This function supports Perl 5 style regular expressions.

Syntax

The RExtract function has the following syntax:

String = RExtract(Expression, Pattern, Flag)

Parameters

The RExtract function has the following parameters.

Table 1. RExtract function parameters
Parameter	Format	Description
`Expression`	String	String that contains the substring to extract. The data to extract is within () in the Expression.
`Pattern`	String	Regular expression pattern that specifies the substring to extract.
`Flag`	true or false	The behavior of the function `RExtract()` changed when Regex libraries were updated in FP3 for IBM Netcool/Impact version 7.1.0. The new library tokenizes `'.'` into two strings: the whole string, and an empty string. Then it returns the last string, which is `NULL`. Set `Flag` to `true` to return the last match (in the case of multiple matches). This is equivalent to the legacy behavior. When `Flag = true` (the default) the last match is returned (in the case of multiple matches). Set `Flag` to `false` to return the entire string, with dot-star (`.`). This is equivalent to legacy behavior. When `Flag = true` (the default) `NULL` is returned instead with dot-star (`.*`) The default setting for this parameter is true.

Return value

The extracted string.

Examples

Example 1

The following example shows how to use the RExtract function.

Log(RExtract("Not responding to ping on host DB_01", ".*\s(DB_01).*"));

This example prints the following message to the policy log:

Parser Log: DB_01

Example 2

The following example shows how to perform a case-insensitive match.

In the pattern parameter, prefix the pattern string with the case insensitive modifier: (?i).

expression = 'application/json;charset=utf-8';
test = Log(RExtract(expression, '(?i)(APPLICATION/JSON)'));
Log(test);

This example prints the following message to the policy log:

[PolicyLogger][testRExtract][pool-4-thread-11]Parser log: application/json

If the expression contains multiple lines and you want the pattern to span across line terminators, use the dotall modifier: (?s).

expression="Line1: IGNORE\r\nBEGIN Line2\r\nLine3\r\nLine4\r\nEND\r\nLine5: IGNORE";
Log(RExtract(expression, "(?s)BEGIN(.*)END"));  // Prints nothing

This example returns a match spanning across several lines:

[PolicyLogger][4REXTRACTSAMPLES][pool-4-thread-11]Parser log:  Line2
Line3
Line4

Example 3

This example shows legacy RExtract behavior.

In the case of multiple matches, return the first one:

expression="<siteId>122</siteId><siteId>204</siteId><siteId>234</siteId>";
test = RExtract(expression, "<siteId\b[^>]*>(.*?)</siteId>",false);
testNum = length(test);
log ("Test Num= " + testNum);
log ("Site ID = " + test);

This example prints the following message to the policy log:

[PolicyLogger]: [testRExtract][pool-3-thread-9]Parser log: Test Num= 3
[PolicyLogger]: [testRExtract][pool-3-thread-9]Parser log: Site ID = 122

In the case of multiple matches, return the last one:

expression="<siteId>122</siteId><siteId>204</siteId><siteId>234</siteId>";
test = RExtract(expression, "<siteId\b[^>]*>(.*?)</siteId>",true);
testNum = length(test);
log ("Test Num= " + testNum);
log ("Site ID = " + test);

This example prints the following message to the policy log:

[PolicyLogger]: [testRExtract][pool-3-thread-9]Parser log: Test Num= 3
[PolicyLogger]: [testRExtract][pool-3-thread-9]Parser log: Site ID = 234

Example 4

This example returns NULL to RExtract, starting with Impact 7.1.0.3.

Log(RExtract("Not responding to ping on host DB_01", ".*"));

This will return and log NULL.

Previously, the legacy version of Impact would return the entire string. To return the entire string, in Impact version 7.1.0.3 or later, set Flag = false (the non-default setting) as in the following example:

Log(RExtract("Not responding to ping on host DB_01", ".*",false));

This will return and log the entire string: Not responding to ping on host DB_01.