bash - What does <<< mean in bash (ie. in socat ... <<<"string" >output-filename)

Question

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?

score 3 · Accepted Answer

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.

score 1 · Accepted Answer

posix shell 版本将是：

echo "show servers state" | socat /tmp/haproxy - > /var/state/haproxy/global

<<<是在标准输入上放一个字符串的基础

score 0 · Accepted Answer

该命令的man页面可能会有所帮助（请注意，这是一个 bash 功能）socatbash<<<

尝试：

man socat
man bash
# Type the following when the bash man page is open
# it will point you right to the explanation of <<<
/<<<

3 回答 3