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I know bash has a >> operator, to append output to files, but what is the use of the << operator?

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up vote 7 down vote accepted


info bash

and then search (type '/' followed by '<<') .
Here's a partial quote:

Here Documents
   This type of redirection instructs the shell to  read  input  from  the
   current source until a line containing only delimiter (with no trailing
   blanks) is seen.  All of the lines read up to that point are then  used
   as the standard input for a command.

   The format of here-documents is:


   No  parameter expansion, command substitution, arithmetic expansion, or
   pathname expansion is performed on word.  If any characters in word are
   quoted,  the  delimiter is the result of quote removal on word, and the
   lines in the here-document are not expanded.  If word is unquoted,  all
   lines  of  the here-document are subjected to parameter expansion, com‐
   mand substitution, and arithmetic expansion.  In the latter  case,  the
   character  sequence  \<newline> is ignored, and \ must be used to quote
   the characters \, $, and `.

   If the redirection operator is <<-, then all leading tab characters are
   stripped  from  input  lines  and  the line containing delimiter.  This
   allows here-documents within shell scripts to be indented in a  natural

Here Strings
   A variant of here documents, the format is:

   The word is expanded and supplied to the command on its standard input. [...]
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$ cat <<EOF
> This is a test
This is a test
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Why did this get a down-vote? (I'd be nice to leave a comment when you down-vote, explaining what the problem is, so that we can fix it) – Stefano Palazzo Jan 14 '11 at 23:18
-1: It's certainly not wrong, but this answer does not explain anything (it's like a "Yes/No" answer). Stefano Palazzo surely gets the idea from this example, but what about different users with the same or a similar question? – htorque Jan 15 '11 at 9:14

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