问题
I am trying to understand a codebase where I see a line like below:
socat /tmp/haproxy - <<< "show servers state" > /var/state/haproxy/global
What is socat doing here? What does <<< mean?
回答1:
The socat command creates a bidirectional pipe between the file /tmp/haproxy and stdin which is expressed by passing - to socat.
In fact it appends stdin to /tmp/haproxy and writes the resulting output to /var/state/haproxy/global
<<< is a bash feature, a so called here string. It passes the string "show server state" as stdin to socat.
回答2:
A posix shell version would be:
echo "show servers state" | socat /tmp/haproxy - > /var/state/haproxy/global
<<< is a bashism to put a string on stdin
回答3:
The man pages of the socat command and bash may help (Note that <<< is a bash feature)
Try:
man socat
man bash
# Type the following when the bash man page is open
# it will point you right to the explanation of <<<
/<<<
来源：https://stackoverflow.com/questions/36036073/what-does-mean-in-bash-ie-in-socat-string-output-filename