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Vedio_315956's avatar
Vedio_315956
Icon for Nimbostratus rankNimbostratus
Mar 31, 2017

Substring syntax in iRules

if { [string length [substr [HTTP::uri] 0 "?"]] > 0 }   IN an above statement I can't able to understand what is the purpose of [ Substr 0 "?" ].   give some suggestion or basic idea about that...
application delivery
iRules
LTM
Kai_Wilke's avatar
Kai_Wilke
Icon for MVP rankMVP
Apr 04, 2017

Hi Charles,

as already outlined by David, a if { [string length [substr [HTTP::uri] 0 "?"]] > 0 } will make no sense at all, since the used 

[substr]
command will extract portion from the beginning of the 
[HTTP::uri]
until the first ocourence of a question mark. This will be always at least a 
/
char, which would then resolve to a 
[string length]
value of at least 
1
.

To check if a HTTP query string (the portion after the first 

?
character) is present you may use one of the iRule snippets below...

Example1: Using a rather simple 

if { X contain Y } then { }
syntax.

if { [HTTP::uri] contains "?" } then {
     A query string is present
} else {
     A query string is NOT present
}

Example2: Using F5s 

[HTTP::query]
command to extract the URI query string.

if { [HTTP::query] ne "" } then {
     A query string is present
} else {
     A query string is NOT present
}

Note: The difference of the two syntaxes is, that the first example will also identify empty query strings (e.g. 

/somepath?
) and the seconds example will only identify query strings with valid parameters (e.g. 
/somepath?param=1
).

Cheers, Kai