Credit for this example goes to “ Checking A Remote Certificate Chain With OpenSSL” from langui.sh.

openssl s_client -showcerts -connect www.andunix.org:443

• s_client: SSL/TLS client program
• -showcerts: display the whole server certificate chain: normally only the server certificate itself is displayed.
• -connect www.andunix.org:443: This specifies the host and optional port to connect to. If not specified then an attempt is made to connect to the local host on port 4433.

$ openssl s_client -showcerts -connect www.andunix.org:443
CONNECTED(00000003)
depth=1 C = GB, ST = Greater Manchester, L = Salford, O = COMODO CA Limited, CN = PositiveSSL CA 2
verify error:num=20:unable to get local issuer certificate
verify return:0
---
Certificate chain
 0 s:/OU=Domain Control Validated/OU=PositiveSSL/CN=www.andunix.org
   i:/C=GB/ST=Greater Manchester/L=Salford/O=COMODO CA Limited/CN=PositiveSSL CA 2
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
 1 s:/C=GB/ST=Greater Manchester/L=Salford/O=COMODO CA Limited/CN=PositiveSSL CA 2
   i:/C=SE/O=AddTrust AB/OU=AddTrust External TTP Network/CN=AddTrust External CA Root
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
---
Server certificate
subject=/OU=Domain Control Validated/OU=PositiveSSL/CN=www.andunix.org
issuer=/C=GB/ST=Greater Manchester/L=Salford/O=COMODO CA Limited/CN=PositiveSSL CA 2
---
No client certificate CA names sent
---
SSL handshake has read 3406 bytes and written 424 bytes
---
New, TLSv1/SSLv3, Cipher is DHE-RSA-AES256-SHA
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
SSL-Session:
    Protocol  : TLSv1
    Cipher    : DHE-RSA-AES256-SHA
    Session-ID: ECA71114A5C89F2F592E5090BEE66086FC3E728BC3EB9778E139F76ECF6760F3
    Session-ID-ctx: 
    Master-Key: 627C22D26C87648687449536C4888198E6383072C03DE3EB19DDC593D4F297AD1FE1118C1C7230C17C7C4C340CBCA803
    Key-Arg   : None
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    TLS session ticket:
    0000 - 69 f0 2c c3 30 7a 5e a6-0a 06 24 4f 8f 1d e2 46   i.,.0z^...$O...F
    0010 - 7c 6d e6 d6 36 03 73 63-80 26 03 3b d9 77 c3 94   |m..6.sc.&.;.w..
    0020 - bb 5f df 12 a4 3e e5 f9-f1 10 54 20 84 53 36 bb   ._...>....T .S6.
    0030 - 95 2a 9d 26 01 d8 1f dc-98 e0 9b 8a 9f a3 69 57   .*.&..........iW
    0040 - 22 35 0d f0 a0 66 d8 69-44 7c f8 ce fa 30 52 06   "5...f.iD|...0R.
    0050 - 23 2b b9 97 a8 15 f4 3e-b9 e0 ea 50 20 11 4a 09   #+.....>...P .J.
    0060 - b9 4b c6 b8 fd 0f d5 5c-63 ad 29 be 60 78 08 f7   .K.....\c.).`x..
    0070 - 43 b6 4d c0 0e ce d4 3d-ca 2d 8c 9c d3 56 04 26   C.M....=.-...V.&
    0080 - 61 cf 53 b5 0e d9 2c 75-6a 59 bb fd 7e ef b3 c3   a.S...,ujY..~...
    0090 - ed 4f ff 97 08 92 9f 1c-35 9f 14 d0 b6 ec 02 97   .O......5.......
    00a0 - 4f 2f 6d 96 4c 63 97 e0-39 bb a3 23 4f ce 04 bf   O/m.Lc..9..#O...
    00b0 - cc a2 b3 5e 7f 9c d3 24-db de 32 0d 55 5a 00 07   ...^...$..2.UZ..

    Start Time: 1361195274
    Timeout   : 300 (sec)
    Verify return code: 20 (unable to get local issuer certificate)
---
^C