bash /dev/tcp check for port

shell/bash-check-port--dev-tcp.md

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+# Shell: check tcp port
+
+Periodically I find myself in th need to check for TCP port availability; and
+no convenient tools available and not possible to install one.
+
+Usually I use `netcat -z -v cidrc port` or telnet.
+
+Lately I've found quite useful some under-appreciated feature of `bash` shell.
+See [/dev/tcp][dev-tcp].
+
+## Example
+
+**Source:** http://stackoverflow.com/a/19866239
+
+```console
+# Connection successful:
+$ timeout 1 bash -c 'cat < /dev/null > /dev/tcp/google.com/80' && echo ping || echo fail
+ping
+```
+
+<!-- References -->
+[dev-tcp]: http://www.tldp.org/LDP/abs/html/devref1.html#DEVTCP "/dev/tcp"