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

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

this is variation of Dennis method, looks more elegant in the scripts.

function definition:

define(){ IFS='\n' read -r -d '' ${1} || true; }

usage:

define VAR <<'EOF'
abc'asdf"
$(dont-execute-this)
foo"bar"''
EOF

echo "$VAR"

enjoy

p.s. made a 'read loop' version for shells that do not support read -d. should work with set -eu and unpaired backticks, but not tested very well:

define(){ o=; while IFS="\n" read -r a; do o="$o$a"'
'; done; eval "$1=\$o"; }

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.

You can avoid a useless use of cat and handle mismatched quotes better with this:

$ read -r -d '' VAR <<'EOF'
abc'asdf"
$(dont-execute-this)
foo"bar"''
EOF

If you don't quote the variable when you echo it, newlines are lost. Quoting it preserves them:

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

If you want to use indentation for readability in the source code, use a dash after the less-thans. The indentation must be done using only tabs (no spaces).

$ read -r -d '' VAR <<-'EOF'
    abc'asdf"
    $(dont-execute-this)
    foo"bar"''
    EOF
$ echo "$VAR"
abc'asdf"
$(dont-execute-this)
foo"bar"''

If, instead, you want to preserve the tabs in the contents of the resulting variable, you need to remove tab from IFS. The terminal marker for the here doc (EOF) must not be indented.

$ IFS='' read -r -d '' VAR <<'EOF'
    abc'asdf"
    $(dont-execute-this)
    foo"bar"''
EOF
$ echo "$VAR"
    abc'asdf"
    $(dont-execute-this)
    foo"bar"''

Tabs can be inserted at the command line by pressing Ctrl-V Tab. If you are using an editor, depending on which one, that may also work or you may have to turn off the feature that automatically converts tabs to spaces.