Linux redirection: << operator

Question

Can anyone explain when and how to use << operator for input redirection? I've googled enough but couldn't find.

That's used for a here document. Allows you to insert text, verbatim, up to <<HERE (position marked in shell by text before <<. — bsd, Apr 22 '15 at 09:10

score 5 · Accepted Answer · answered Apr 22 '15 at 09:11

The << redirection operator introduces a "here document": the text fed into standard input comes just after the redirection.

Here's an example:

grep Hello <<EOF
This line won't appear
Hello this one will
Hello again
EOF

All the text between <<EOF and EOF is fed into grep. EOF isn't special here, the shell takes the word given just after << and uses it as a delimiter.

An interesting variant is <<- which strips leading tabs.

See the bash documentation for details.

score 3 · Answer 2 · answered Apr 22 '15 at 09:10

This operator is used for multiline redirect. See below for example

program <<KEYWORD
line1
line2
line3
KEYWORD

The above send line1, line2, line3 strings, delimited with newline

You should not have KEYWORD (can be any other word) in the text. And last line with KEYWORD should start from begin, no space, no tab, etc

Linux redirection: << operator

2 Answers2