Here
Document
we
are pretty much aware of the re direction in Linux .When we use
#
echo 'hello world' >output
#
cat <output
The
first line writes "hello world" to the file "output",
the second reads it back and writes it to standard output ( To
Terminal)
Then
there are "here" documents:
#
cat <<EOF
>
hello
>
world
>
EOF
A
"here" document is essentially a temporary, nameless file
that is used as input to a command, here the "cat" command.
A
less commonly seen form of here document is the "here"
string:
#
cat <<<'hello world'
In
this form the string following the "<<<" becomes
the content of the "here" document.
This
type of redirection tells the shell to read input from the current
source (HERE) until a line containing only word (HERE) is seen. HERE
word is not subjected to variable name, parameter expansion,
arithmetic expansion, path name expansion, or command substitution.
All of the lines read up to that point are then used as the standard
input for a command. Files are processed in this manner are commonly
called here documents.
Here
Docs
wc
-w <<EOF
>
This is a test.
>
Apple juice.
>
100% fruit juice and no added sugar, colour or preservative.
>
EOF
Here
Strings
Command
<<<$word
wc -w <<<
"This is a test."
