container ls --filter name , regex start anchor has an awkward behavior

BUG REPORT INFORMATION

Description

The --filter option for container ls seem to support regex. For example you can use classes ([abc]), quantifiers (*,+,{x}), end anchor ($). But for some reason using start anchor (^) does not lead to expected results.

Steps to reproduce the issue:

1. From any image, create or run 3 named (--name) containers: a1, a2, ba2.
2. Run docker container ls -aqf name=^a

Describe the results you received:
Empty list of containers ids

Describe the results you expected:
A list of container ids, whose name starts with an a character.

Additional information you deem important (e.g. issue happens only occasionally):

It does not matter, whether the container runs or not. Not only because I used the -a flag, but also because I have tested both with containers running and not. The issue is equal in both cases.

I did not find any info on the official docs for container ls regarding the --filter option, but I did test different regex patterns and they worked. For example, having the above containers a1, a2, ba2, I could fetch ba2 using -aqf name=[ab]{2}.

I executed the exact same test with named networks a1, a2, ba2. Contrary to container ls the result matched the expectation.

Output of docker version:

Client:
 Version:      18.03.1-ce
 API version:  1.37
 Go version:   go1.9.5
 Git commit:   9ee9f40
 Built:        Thu Apr 26 07:17:20 2018
 OS/Arch:      linux/amd64
 Experimental: false
 Orchestrator: swarm

Server:
 Engine:
  Version:      18.03.1-ce
  API version:  1.37 (minimum version 1.12)
  Go version:   go1.9.5
  Git commit:   9ee9f40
  Built:        Thu Apr 26 07:15:30 2018
  OS/Arch:      linux/amd64
  Experimental: false

Output of docker info:

Containers: 6
 Running: 6
 Paused: 0
 Stopped: 0
Images: 47
Server Version: 18.03.1-ce
Storage Driver: overlay2
 Backing Filesystem: extfs
 Supports d_type: true
 Native Overlay Diff: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
 Volume: local
 Network: bridge host macvlan null overlay
 Log: awslogs fluentd gcplogs gelf journald json-file logentries splunk syslog
Swarm: inactive
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 773c489c9c1b21a6d78b5c538cd395416ec50f88
runc version: 4fc53a81fb7c994640722ac585fa9ca548971871
init version: 949e6fa
Security Options:
 apparmor
 seccomp
  Profile: default
Kernel Version: 4.15.0-24-generic
Operating System: Ubuntu 16.04.4 LTS
OSType: linux
Architecture: x86_64
CPUs: 16
Total Memory: 15.68GiB
Name: xxx
ID: ICQC:MWTE:VWKT:5Z2W:VCKA:W2O5:2BSZ:6GEZ:K5B2:Y7XK:MMMJ:HYDS
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): false
Registry: https://index.docker.io/v1/
Labels:
Experimental: false
Insecure Registries:
 127.0.0.0/8
Live Restore Enabled: false

WARNING: No swap limit support

Additional environment details (AWS, VirtualBox, physical, etc.):

Physical machine

Start by tracing the docker container ls --filter name handling and compare it with the named-network filter behavior described in the report. Add a regression case using containers named a1, a2, and ba2 with the ^a filter, then verify that only names beginning with a are returned.