在grep期间抑制Openssl输出

Question

grep在测试TLS安全性时,我经常使用openssl结果.例如:

$ openssl s_client -tls1_2 -connect 172.11.15.32:443 </dev/null | grep 'IS s'
depth=0 C = US, ST = asd, O = Billing, CN = asdasd, emailAddress = root@asdasd
verify error:num=18:self signed certificate
verify return:1
depth=0 C = US, ST = asd, O = Billing, CN = asdasd, emailAddress = root@asdasd
verify return:1
DONE
Secure Renegotiation IS supported

然而,问题是,无论我的grep是什么,输出始终包含这些(或类似的)行:

depth=0 C = US, ST = asd, O = Billing, CN = asdasd, emailAddress = root@asdasd
    verify error:num=18:self signed certificate
    verify return:1
    depth=0 C = US, ST = asd, O = Billing, CN = asdasd, emailAddress = root@asdasd
    verify return:1

是否有可能以某种方式抑制这些消息并只接收grep结果？

Answer 1

如注释中所示,问题是该命令openssl显示其输出的一部分stderr.然后,无论你管道什么,这都会显示出来.

因此,如果您只想显示grep过滤给您的内容,您必须先重定向stderr到/dev/null这样才能"跳过管道":

openssl ... 2>/dev/null | grep 'IS s'
#           ^^^^^^^^^^^

看另一个例子:

$ touch hello
$ ls hello adlsfjaskldf
ls: cannot access adlsfjaskldf: No such file or directory  # stderr
hello                                                      # stdout

让grep,出现一切:

$ ls hello adlsfjaskldf | grep hello
ls: cannot access adlsfjaskldf: No such file or directory  # stderr
hello                                                      # stdout

让我们grep但事先重定向stderr:

$ ls hello adlsfjaskldf 2>/dev/null | grep hello
hello                                      # no "ls: cannot access..." here