What does “<<<” mean on a bash command line? And where is it documented?

Question

What does <<< mean in this command line?

bc <<< "1 + 1"

It doesn't seem to a combination of < and << , and I can't find documentation for it. It seems to behave just like

echo "1 + 1" | bc

Also works in ksh , but not in sh .

Answer 1

It introduces a here string, documented near the end of the section on input and output redirections. A here string is just a one-word here document:

bc <<< "1 + 1"

is equivalent to

bc <<EOF
1 + 1
EOF

Answer 2

That is the here string operator. See here string operator document.

Answer 3

man ksh

您可以通过键入/（斜杠）后跟要搜索的内容（例如使用更少的程序）来在手册中执行搜索。