Using Regular Expressions in SNMP Probes
InterMapper SNMP probes can evaulate regular expressions (regex) to parse strings that are returned from a device. This note describes how to use regexes in SNMP probes.
Special Characters in InterMapper Regular Expressions:
- \\s matches white space (note the "\\" are required to escape the pattern)
- \\X escapes the character "X" (note the "\\" are required to escape a character)
- [0-9] matches a single digit
- [a-z] matches a single lower-case character
- [A-Z] matches a single upper-case character
- [a-zA-Z] matches a single alpha character - upper or lower case
Example:
A piece of equipment returns three important pieces of information encoded in a single string with this format:
The goal was to separate these three parts: "Status", "123", and "msec" into separate variables. Here is a portion of the SNMP probe that did the calculations:
| Code: |
<parameters>
StringToMatch = "Status (123 msec)"
</parameters>
<snmp-device-variables>
-- parse out input of the form "alpha (digits alpha)"
-- $pat1 is the pattern,
-- str0 forces the string ($RT110951) to be matched against the pattern pat1
-- str1, str2, str3 will have the resulting strings
pat1, "([a-zA-Z]+)\\s*\\(\\s*([0-9]+)\\s*([a-zA-Z]+)\\s*)", CALCULATION, ""
str0, "$StringToMatch" =~ "$pat1", CALCULATION, ""
str1, "${1}", CALCULATION, ""
str2, "${2}", CALCULATION, ""
str3, "${3}", CALCULATION, ""
</snmp-device-variables> |
Here's how it works:
- The first line (pat1) is the pattern to match. It has several interesting components:
- ([a-zA-Z]+) - a remembered pattern of 1 or more letters from the class a-z or A-Z
- \\s* - zero or more whitespace characters (you need the "\\")
- [(] - a literal "(" - you could also escape it with "\\" - that is "\\(" would work too
- ([0-9]+) - a remembered pattern of one or more digits (second pattern)
- \\s* - more white space
- ([a-zA-Z]+) - a remembered pattern of one or more letters (third pattern)
- [)] - a literal closing parenthesis
- The second line (str0) forces the parameter ($StringToMatch) to be matched against the pattern from line 1. This action sets the values of the three variables ${1}, ${2}, ${3} to the three remembered patterns within the parentheses of the $pat1.
- The next three lines set the variables str1, str2, str3 to the three remembered patterns. These variables can be used elsewhere in the probe.
Note: The following items all must be enclosed in "..." double-quotes in the <snmp-device-variables> section. This forces the values to be treated as string values.
"$StringToMatch"
"$pat1"
"([a-zA-Z]+)\\s*[(]([0-9]+)\\s*([a-zA-Z]+)[)]"
"${1}"
"${2}"
"${3}"
Example Probe File:
A complete probe that shows this technique
