Forum Discussion

Nimbostratus

Jan 25, 2016

Undefined Procedure with elseif when using comments

I am having trouble committing the following iRule when adding in comments above the elseif statements. It always interprets the first comment it finds above an elseif statement as the offender.

01070151:3: Rule [/Common/Main_Website_80_Revised] error: /Common/Main_Website_80_Revised:7: error: [undefined procedure: elseif][elseif {[class match [HTTP::host] eq group_80_encrypt]} {
HTTP::redirect https://[getfield [HTTP::host] ":" 1][HTTP::uri]
}]

Removing all comments (aside from line 2, that one seems fine) will commit the iRule without any issue. Any idea what might be going on?

when HTTP_REQUEST {
    302 redirect to a different URL based on hostname
    if {[class match [HTTP::host] eq group_80_host_redirect]} {
        HTTP::redirect [class match -value [HTTP::host] eq group_80_host_redirect]
    }
    302 redirect to enforce HTTPS based on hostname or URI
    elseif {[class match [HTTP::host] eq group_80_encrypt]} {
        HTTP::redirect https://[getfield [HTTP::host] ":" 1][HTTP::uri]
    }
    Pool selection based on hostname
    elseif {[class match [HTTP::host] eq group_80_host_pool]} {
        pool [class match -value [HTTP::host] eq group_80_host_pool]
    }
    Pool selection based on URI
    elseif {[class match [HTTP::uri] starts_with group_80_uri_pool]} {
        pool [class match -value [HTTP::uri] starts_with group_80_uri_pool]
    }
    else {
        pool Main_80_Pool
    }
}

Vernon_97235
Jan 25, 2016
This results from a peculiarity of Tcl. The language doesn't really have built-ins and it doesn't really have blocks. Rather, it has commands and non-interpolated quoted strings. As such,
if
is a command (just like
split
or
HTTP::headers
). It is followed by a quoted block (the {}s, in Tcl, are really non-interpolating quoting operators, and not really block delimiters as they are in most languages). The quoted block may then be optionally followed by zero or more
elseif
literals (each followed by a quoted block) and zero or one
else
literals (followed by a quoted block). When a condition is met, the contents of the corresponding quoted block are evaluated.

Said another way, in Tcl, an
if
/
elseif
/
else
set is really a single statement. The statement command is
if
. The
elseif
and
else
are just parameters to this command. And because the newlines in the blocks are ignored by the parser (because they are inside of the non-interpolating {} quoting operators), the entire statement is effectively on one line.

As a side-effect of this, in Tcl you MUST cuddle an
if
/
elseif
/
else
block, as in:

if { ... } { ... } else { ... }

This is not allowed:

if { ... } { ... } else { ... }

However, this trips up most programmers, so iRules (a Tcl dialect) allows non-cuddled
if
blocks. But if you add a comment between the control elements, this effectively inserts a newline. So, with the comments you have above, the parser "sees" this:

if { ... } elseif { ... } else { ... }

which it thinks is really three different commands:
if
,
elseif
and
else
. Only
if
is a command; the others are not (again, they are just parameters of the
if
command).

Okay, so that's really just a long-winded way of saying: you must move those comments inside the squirly braces ({}). 🙂

VernonWells
Employee
Jan 25, 2016
This results from a peculiarity of Tcl. The language doesn't really have built-ins and it doesn't really have blocks. Rather, it has commands and non-interpolated quoted strings. As such,
if
is a command (just like
split
or
HTTP::headers
). It is followed by a quoted block (the {}s, in Tcl, are really non-interpolating quoting operators, and not really block delimiters as they are in most languages). The quoted block may then be optionally followed by zero or more
elseif
literals (each followed by a quoted block) and zero or one
else
literals (followed by a quoted block). When a condition is met, the contents of the corresponding quoted block are evaluated.

Said another way, in Tcl, an
if
/
elseif
/
else
set is really a single statement. The statement command is
if
. The
elseif
and
else
are just parameters to this command. And because the newlines in the blocks are ignored by the parser (because they are inside of the non-interpolating {} quoting operators), the entire statement is effectively on one line.

As a side-effect of this, in Tcl you MUST cuddle an
if
/
elseif
/
else
block, as in:

if { ... } { ... } else { ... }

This is not allowed:

if { ... } { ... } else { ... }

However, this trips up most programmers, so iRules (a Tcl dialect) allows non-cuddled
if
blocks. But if you add a comment between the control elements, this effectively inserts a newline. So, with the comments you have above, the parser "sees" this:

if { ... } elseif { ... } else { ... }

which it thinks is really three different commands:
if
,
elseif
and
else
. Only
if
is a command; the others are not (again, they are just parameters of the
if
command).

Okay, so that's really just a long-winded way of saying: you must move those comments inside the squirly braces ({}). 🙂
- cody8411_186897
  Nimbostratus
  Jan 25, 2016
  Excellent explanation. That definitely makes sense now that I understand how the code is interpreted in Tcl. Moved the comments down inside the commands and worked as expected, thank you!
Vernon_97235
Historic F5 Account
Jan 25, 2016
This results from a peculiarity of Tcl. The language doesn't really have built-ins and it doesn't really have blocks. Rather, it has commands and non-interpolated quoted strings. As such,
if
is a command (just like
split
or
HTTP::headers
). It is followed by a quoted block (the {}s, in Tcl, are really non-interpolating quoting operators, and not really block delimiters as they are in most languages). The quoted block may then be optionally followed by zero or more
elseif
literals (each followed by a quoted block) and zero or one
else
literals (followed by a quoted block). When a condition is met, the contents of the corresponding quoted block are evaluated.

Said another way, in Tcl, an
if
/
elseif
/
else
set is really a single statement. The statement command is
if
. The
elseif
and
else
are just parameters to this command. And because the newlines in the blocks are ignored by the parser (because they are inside of the non-interpolating {} quoting operators), the entire statement is effectively on one line.

As a side-effect of this, in Tcl you MUST cuddle an
if
/
elseif
/
else
block, as in:

if { ... } { ... } else { ... }

This is not allowed:

if { ... } { ... } else { ... }

However, this trips up most programmers, so iRules (a Tcl dialect) allows non-cuddled
if
blocks. But if you add a comment between the control elements, this effectively inserts a newline. So, with the comments you have above, the parser "sees" this:

if { ... } elseif { ... } else { ... }

which it thinks is really three different commands:
if
,
elseif
and
else
. Only
if
is a command; the others are not (again, they are just parameters of the
if
command).

Okay, so that's really just a long-winded way of saying: you must move those comments inside the squirly braces ({}). 🙂
- cody8411_186897
  Nimbostratus
  Jan 25, 2016
  Excellent explanation. That definitely makes sense now that I understand how the code is interpreted in Tcl. Moved the comments down inside the commands and worked as expected, thank you!
Salvador_del_Re
Historic F5 Account
Feb 24, 2016
I have the same problema. I insert the comments below and don´t have issues if {[class match [HTTP::host] eq group_80_host_redirect]} { HTTP::redirect [class match -value [HTTP::host] eq group_80_host_redirect] 302 redirect to a different URL based on hostname } elseif {[class match [HTTP::host] eq group_80_encrypt]} { HTTP::redirect https://[getfield [HTTP::host] ":" 1][HTTP::uri] 302 redirect to enforce HTTPS based on hostname or URI }