What is the difference between the two commands?
Show run vlan # = blank output
show run int vlan # = vlan configuration
Likewise:
show vlans
No virutal LANs configured
show vlan
A bunch of output displaying interfaces and their respective vlans.
What is the difference between the two?
The "show run int" shows the portion of the configuration in NVRAM that defines the actual interface. The second command (sh vlan) actually shows the live state of the VLAN's (nb - sh vlan id xxx for a single VLAN ID, if platform supports it) as actively kept in switch's database. One command shows the actual configuration, the other a portion of the running state.
The first is the result of part 'vlan XXX' and the second concerns 'interface vlan XXX'. The first is the definition of vlans and the second the definition of interface Vlan (with IP address). On my switches, the first is always empty as the VLANs are not defined in the running-config but in the vlan database. The seconds concerns the interface Vlan with the IP address, etc.
In my case show vlans doesn't exists.
You could see the vlans created in vlan database / show
