Less than symbol <<<

<<< denotes a here string.


$ cat <<< 'hi there'
hi there

It passes the word on the right to the standard input of the command on the left.

<< denotes a here document.


$ cat <<EOF
> hi
> there
> EOF
hi
there

EOF can be any word.

Here documents are commonly used in shell scripts to create whole files or to display long messages.


cat > some-file <<FILE
foo
bar
bar bar
foo foo
FILE

< passes the contents of a file to a command's standard input.


$ cat < /etc/fstab
/dev/sda2               /boot   ext4            nosuid,noexec,nodev,rw,noatime,nodiratime       0 2
/dev/sda4               /       ext4            rw,noatime,nodiratime,  0 1
/dev/sdb5               /var    ext4            nosuid,noexec,nodev,rw,relatime 0 2
 ...