Correct textual name for <<

Question

I've just come across the << command, used like so:

cat > outfile.txt <<EOF
Multi-line content
that will be written to outfile.txt
EOF

Now, I've no idea what this is called, but I'd quite like to know it's name, primarily so I can go and search and find out more about its syntax. Sadly, Googling for "<<" just doesn't work.

Conveniently, I was just trying to figure out how to use it with a stdout redirection last night and couldn't get it. I kept trying to do EOF > outfile.txt at the end, which doesn't work well — Michael Mrozek, Oct 08 '10 at 14:07
POSIX 2008 > Shell Command Language > Redirection > Here-Document — jw013, Mar 23 '12 at 05:47
man bash and look for << (in my man viewer, the search command is the / character, so /<< gets me to the right section). — jfg956, Mar 23 '12 at 08:33
For an experiment, you should have tried 'cat <<HERE'. echo doesn't read stdin. — XTL, Mar 23 '12 at 15:02
possible duplicate of How does << work and what is it called? — Gilles 'SO- stop being evil', Mar 23 '12 at 18:55
See also What are the shell's control and redirection operators? — Scott - Слава Україні, Sep 11 '16 at 06:19
Most shells also supports cat <<< this line is fed to cat (a one-line here-doc) which can be handy sometimes. — olejorgenb, Sep 20 '16 at 02:29

score 17 · Accepted Answer · answered Oct 08 '10 at 13:25

17

That's called a "Here document".

http://en.wikipedia.org/wiki/Here_document

answered Oct 08 '10 at 13:25

developmentalinsanity

1,086

score 8 · Answer 2 · edited Nov 27 '21 at 11:11

8

It's form of redirection called a here document or heredoc. It redirects the contents of the given in-line document to a command. The document is delimited by the given word (EOT below). Quoting the word or part of the word after << creates a quoted here-document that the shell will not perform expansions in.

$ tac << EOT
> 123
> 456
> EOT
456
123

edited Nov 27 '21 at 11:11

Kusalananda

333,661

answered Mar 23 '12 at 05:18

Ignacio Vazquez-Abrams

45,725

score 1 · Answer 3 · answered Mar 23 '12 at 05:34

1

In a Unix context it really is known as a "here document." I believe that the "heredoc" construct comes from PHP, Perl, and other scripting languages, and for shell scripting I'd tend to stick with "here document."

answered Mar 23 '12 at 05:34

Melinda

211

Correct textual name for <<

3 Answers3

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