How to check if value is empty?

payday · Sat Nov 09, 2013 12:55 am

In RouterOS version before 6.2 the following command returned items with empty comments:

/interface> print count-only where !comment
3

In current version of ROS it always returns 0. Don't know if it is a bug or new feature.

How to produce the same old result using current version?
What condition should be put in where to check if comment is empty?

Sat Nov 09, 2013 11:56 am

"!comment" is supposed to find items where a comment is not set. Previously, "not set" was treated as an equivalent of "empty", but that's not technically true, so this new behavior is IMHO the correct one.

To check for empty-ness, just compare against an empty string, i.e.

print where comment=""

payday · Sun Nov 10, 2013 11:06 pm

I've checked that and it does not work.
I've also checked this:

/interface wireless access-list> print count-only where !(comment)
0
/interface wireless access-list> print count-only where (comment) 
0
/interface wireless access-list> print count-only where comment  
0
/interface wireless access-list> print count-only where comment=""
0
/interface wireless access-list> print count-only where comment=nil
0
/interface wireless access-list> print count-only where comment=nothing
0
/interface wireless access-list> print count-only where comment=:nothing
0
/interface wireless access-list> print count-only where comment=:nil    
0
/interface wireless access-list> print count-only where !comment   
0
/interface wireless access-list> print count-only where (!comment)
0

I have two items without comment so I am expecting to get 2 as a result.

payday · Sun Nov 10, 2013 11:31 pm

BINGO!

Trying other combinations:

/interface wireless access-list> print count-only where not comment
0
/interface wireless access-list> print count-only where comment~"" 
89

Last one returned numer of all items on the list - with and without comment - strange.
So, another try:

/interface wireless access-list> print count-only where !comment~""
2

This returned numer of items without comment.

This is working on ROS 6.6. I will see for how long will it work (until MikroTik change it again)....

vipe · Mon Nov 11, 2013 11:54 am

These no longer work in v6.2 and v6.3:
:put [:len [/ip route find !routing-mark]]
:put [:len [/interface find !comment]]

The alternative syntax suggested in viewtopic.php?f=2&t=75894, with parentheses around !routing-mark and !comment, always returns nothing (len=zero).

Is this a bug or am I missing something?

Thanks for your help...

5.26

Similarly for !status
:put [:len [/ip dhcp-server lease find !status]]

( :put [:len [/ip dhcp-server lease find status=""]]
does not return any results either )

This seems to be a generic issue with the not operator when used in a [set/get find] and [print where] context. Am I right?

paoloaga · Fri Apr 18, 2014 9:55 pm

/interface wireless access-list> print count-only where !comment~""
2[/code] This returned numer of items without comment.

This is working on ROS 6.6. I will see for how long will it work (until MikroTik change it again)....

I think that's better this way:

:put [/ip route find where dst-address="0.0.0.0/0" && routing-mark~"^\$" ]

because the "~" operator matches against a regular expression. To match an empty string you can use "^\$". I think that using !item~"" works by luck.

Chupakabra303 · Thu May 16, 2019 4:47 pm

Magic word "any":
[find where !any routing-mark and dst-address=0.0.0.0/0 and active=yes]

Jooocker · Sun Aug 30, 2020 10:47 pm

You can use [] to refer to empty value.
LIKE THIS:
where !comment=[]

Example:

foreach i in=[ /tool user-manager user find where comment=[] ] do={ put [ /tool user-manager user get $i username ] }

This will give you all usernames they don't have comment .

eworm · Wed Sep 02, 2020 12:26 am

For the inversion you have to use parenthesis:

... where !(comment=[])

Really nice to have this... Is this documented anywhere?

eworm · Wed Sep 02, 2020 12:30 am

Answering myself... Looks like this is executing an empty command, which evaluates to "nil":

[admin@mt] > :put [ :typeof [] ]
nil

How to check if value is empty?

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