[bash] How to assign a heredoc value to a variable in Bash?

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...

There is still no solution that preserves newlines.

This is not true - you're probably just being misled by the behaviour of echo:

echo $VAR # strips newlines

echo "$VAR" # preserves newlines

I found myself having to read a string with NULL in it, so here is a solution that will read anything you throw at it. Although if you actually are dealing with NULL, you will need to deal with that at the hex level.

$ cat > read.dd.sh

read.dd() {
     buf= 
     while read; do
        buf+=$REPLY
     done < <( dd bs=1 2>/dev/null | xxd -p )

     printf -v REPLY '%b' $( sed 's/../ \\\x&/g' <<< $buf )
}

Proof:

$ . read.dd.sh
$ read.dd < read.dd.sh
$ echo -n "$REPLY" > read.dd.sh.copy
$ diff read.dd.sh read.dd.sh.copy || echo "File are different"
$ 

HEREDOC example (with ^J, ^M, ^I):

$ read.dd <<'HEREDOC'
>       (TAB)
>       (SPACES)
(^J)^M(^M)
> DONE
>
> HEREDOC

$ declare -p REPLY
declare -- REPLY="  (TAB)
      (SPACES)
(^M)
DONE

"

$ declare -p REPLY | xxd
0000000: 6465 636c 6172 6520 2d2d 2052 4550 4c59  declare -- REPLY
0000010: 3d22 0928 5441 4229 0a20 2020 2020 2028  =".(TAB).      (
0000020: 5350 4143 4553 290a 285e 4a29 0d28 5e4d  SPACES).(^J).(^M
0000030: 290a 444f 4e45 0a0a 220a                 ).DONE

assign a heredoc value to a variable

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

used as an argument of a command

echo "$(cat <<'SQLEOF'
xxx''xxx'xxx'xx  123123    123123
abc'asdf"
$(dont-execute-this)
foo"bar"''
SQLEOF
)"

Thanks to dimo414's answer, this shows how his great solution works, and shows that you can have quotes and variables in the text easily as well:

example output

$ ./test.sh

The text from the example function is:
  Welcome dev: Would you "like" to know how many 'files' there are in /tmp?

  There are "      38" files in /tmp, according to the "wc" command

test.sh

#!/bin/bash

function text1()
{
  COUNT=$(\ls /tmp | wc -l)
cat <<EOF

  $1 Would you "like" to know how many 'files' there are in /tmp?

  There are "$COUNT" files in /tmp, according to the "wc" command

EOF
}

function main()
{
  OUT=$(text1 "Welcome dev:")
  echo "The text from the example function is: $OUT"
}

main

An array is a variable, so in that case mapfile will work

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

Then you can print like this

printf %s "${y[@]}"

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.

Branching off Neil's answer, you often don't need a var at all, you can use a function in much the same way as a variable and it's much easier to read than the inline or read-based solutions.

$ complex_message() {
  cat <<'EOF'
abc'asdf"
$(dont-execute-this)
foo"bar"''
EOF
}

$ echo "This is a $(complex_message)"
This is a abc'asdf"
$(dont-execute-this)
foo"bar"''

$TEST="ok"
read MYTEXT <<EOT
this bash trick
should preserve
newlines $TEST
long live perl
EOT
echo -e $MYTEXT

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