How to assign a heredoc value to a variable in Bash?

user_14193 0
Viewed 249301

I have this multi-line string (quotes included):

abc'asdf"
$(dont-execute-this)
foo"bar"''

How would I assign it to a variable using a heredoc in Bash?

I need to preserve newlines.

I don't want to escape the characters in the string, that would be annoying...

heredoc bash
13 Answers

Use $() to assign the output of cat to your variable like this:

VAR=$(cat <<'END_HEREDOC'
abc'asdf"
$(dont-execute-this)
foo"bar"''
END_HEREDOC
)

# this will echo variable with new lines intact
echo "$VAR"
# this will echo variable without new lines (changed to space character)
echo $VAR

Making sure to delimit starting END_HEREDOC with single-quotes.

Note that ending heredoc delimiter END_HEREDOC must be alone on the line (hence ending parenthesis is on the next line).

Thanks to @ephemient for the answer.

user_141930 
VAR=<<END
abc
END

doesn't work because you are redirecting stdin to something that doesn't care about it, namely the assignment

export A=`cat <<END
sdfsdf
sdfsdf
sdfsfds
END
` ; echo $A

works, but there's a back-tic in there that may stop you from using this. Also, you should really avoid using backticks, it's better to use the command substitution notation $(..).

export A=$(cat <<END
sdfsdf
sdfsdf
sdfsfds
END
) ; echo $A
user_51000

I can't believe I'm the first to post this.

@Erman and @Zombo are close, but mapfile doesn't just read arrays...

Consider this:

#!/bin/bash
mapfile -d '' EXAMPLE << 'EOF'
Hello
こんにちは
今晩は
小夜なら
EOF
echo -n "$EXAMPLE"

Yielding:

Hello
こんにちは
今晩は
小夜なら

$'' is the delimiter given to mapfile, it will never occur, it means "not delimited".

So there's no need for a useless use of cat and no need to incur the penalty of recombining arrays.

Furthermore, you get this benefit:

$ echo $EXAMPLE
Hello こんにちは 今晩は 小夜なら

Which you do not receive with @Zombo's method:

mapfile y <<'z'
abc'asdf"
$(dont-execute-this)
foo"bar"''
z
echo $y

abc'asdf"

Bonus

If you run it through head -c -1 you can also get rid of that last newline in a way that won't be non-performant:

unset EXAMPLE
mapfile -d '' EXAMPLE < <(head -c -1 << EOF
Hello
こんにちは
今晩は
小夜なら
EOF
)
printf "%q" "$EXAMPLE"

$'Hello\nこんにちは\n今晩は\n小夜なら'
user_19016580

Here's a way to do it that is (imho) quite elegant and avoids a UUOC:

  VAR=$(sed -e 's/[ ]*\| //g' -e '1d;$d' <<'--------------------'
      | 
      | <!DOCTYPE html>
      | <html>
      |   <head>
      |     <script src='script.js'></script>
      |   </head>
      |   <body>
      |     <span id='hello-world'></span>
      |   </body>
      | </html>
      | 
--------------------
    )

The '|' characters define the margin, and only the whitespace to the right of the margin is respected in the printed string. The '1d;$d' strips the first and last line, which are just added as a top and bottom margin around the content. Everything can be indented to whatever level you like, except the HEREDOC delimiter, which in this case is just a bunch of hyphens.

echo "$VAR"

# prints

<!DOCTYPE html>
<html>
  <head>
    <script src='script.js'></script>
  </head>
  <body>
    <span id='hello-world'></span>
  </body>
</html>
user_29254340
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