Substitute - a simple iRule script to simulate apache mod_substitute

Problem this snippet solves:

Sometimes it is neccessary to rewrite some stuff in delivered HTTP-Content. Here we have a simple way to search an replace these thinks.

How to use this snippet:

If you want to use these script you have to provide a data group with type string named


Here each line have the format


Code :

when RULE_INIT {
# Enable to debug Substitute translations via log messages in /var/log/ltm
# (2 = verbose, 1 = essential, 0 = none)
set static::SubstituteDebug 0


set static::log_prefix "[IP::client_addr]:[TCP::local_port]:"

# Disable the stream filter for all requests

# The name of the Data Group (aka class) we are going to use. 
# Parse just the virtual server name by stripping off the folders (if present)
set class_name "Substitute_[URI::basename [virtual name]]"

if { $static::SubstituteDebug > 1 } {
log local0. "$static::log_prefix [IP::client_addr]:[TCP::client_port] -> [IP::local_addr]:[TCP::local_port]"

# disable stream by default
if { $static::SubstituteDebug > 1}{
log local0. "$static::log_prefix: disable stream per default"

# Create all essential variables for the logic below
# set all variables to an empty value
set regexreplace ""
set regex ""
set replace ""

# Check whether class_name exist or not.
# If it doesn't exists log an that the data group is missing an exiting
if {! [class exists $class_name]} {
log local0. "$log_prefix: Data group $class_name not found, exiting."
} else {
# Here we know that the needed data group exists and we can go on
# set id for iteration purpose
set id [class startsearch $class_name]

# iterate over data group list to get all regex replace pairs 
while {[class anymore $class_name $id]}{
# save actual line of data group in element
# extract regex and replace from element
set element [class nextelement $class_name $id]
set regex [getfield $element " " 1]
set replace [getfield $element " " 2 ]

if { $static::SubstituteDebug > 1} {
log local0. "$log_prefix: regex=$regex, replace=$replace"

# and build a string with all regex replace pairs
set regexreplace "@$regex@$replace@ $regexreplace"

if { $static::SubstituteDebug > 1} {
log local0. "$log_prefix: regexreplace=$regexreplace"

# if regexreplace is set 
if {$regexreplace ne ""}{
# and content-type equals text
if {[HTTP::header value Content-Type] contains "text"}{
if { $static::SubstituteDebug > 1} {
log local0. "$log_prefix: try STREAM::expression [string trim $regexreplace " "]"
# apply regexreplace pairs to stream
STREAM::expression [string trim $regexreplace " "]

if { $static::SubstituteDebug > 1}{
log local0. "$log_prefix: enable stream"

# Enable the stream filter for this response only

Tested this on version:

Updated Jun 06, 2023
Version 2.0

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