How to specify a multi-line shell variable?

Question

simply insert new line where necessary

sql="
SELECT c1, c2
from Table1, Table2
where ...
"

shell will be looking for the closing quotation mark

Use read with a heredoc as shown below:

read -d '' sql << EOF
select c1, c2 from foo
where c1='something'
EOF

echo "$sql"

I would like to give one additional answer, while the other ones will suffice in most cases.

I wanted to write a string over multiple lines, but its contents needed to be single-line.

sql="                       \
SELECT c1, c2               \
from Table1, ${TABLE2}      \
where ...                   \
"

I am sorry if this if a bit off-topic (I did not need this for SQL). However, this post comes up among the first results when searching for multi-line shell variables and an additional answer seemed appropriate.

Thanks to dimo414's answer to a similar question, 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

read does not export the variable (which is a good thing most of the time). Here's an alternative which can be exported in one command, can preserve or discard linefeeds, and allows mixing of quoting-styles as needed. Works for bash and zsh.

oneLine=$(printf %s \
    a   \
    " b "   \
    $'\tc\t'    \
    'd '    \
)
multiLine=$(printf '%s\n' \
    a   \
    " b "   \
    $'\tc\t'    \
    'd '    \
)

I admit the need for quoting makes this ugly for SQL, but it answers the (more generally expressed) question in the title.

I use it like this

export LS_COLORS=$(printf %s    \
    ':*rc=36:*.ini=36:*.inf=36:*.cfg=36:*~=33:*.bak=33:*$=33'   \
    ...
    ':bd=40;33;1:cd=40;33;1:or=1;31:mi=31:ex=00')

in a file sourced from both my .bashrc and .zshrc.