Obtaining MD5 hash of a string

MD5 produces a binary object in iRules.

https://devcentral.f5.com/wiki/iRules.md5.ashx

To see what you'd expect from something like md5sum, do a binary scan and convert to hex:

 
when HTTP_REQUEST {
set var1 "this is a test"
binary scan [md5 $var1] H* key
log local0. $key
}

** create a file and enter "this is a test" as its contents, then run md5sum against that file. You'll get the same value.