Why can't I generate newlines in quotes in bash? - bash

Question

No matter what I do, I can't get the newlines in quotes to persist in the output. What am I to do? This is bash in OS X. My code is here: Gist
read -d '' sbt_text=$(cat <<"EOF"
#!/bin/bash
SBT_OPTS="-Xms512M -Xmx1536M -Xss1M -XX:+CMSClassUnloadingEnabled -XX:MaxPermSize=256M";
java $SBT_OPTS -jar `dirname $0`/sbt-launch.jar "$#"
EOF
)
echo $sbt_text
#!/bin/bash > SBT_OPTS="-Xms512M -Xmx1536M -Xss1M -XX:+CMSClassUnloadingEnabled -XX:MaxPermSize=256M"; > java -jar /sbt-launch.jar ""

Answer 1

What you probably want is this:
IFS= read -d '' -r sbt_text <<"EOF"
#!/bin/bash
SBT_OPTS="-Xms512M -Xmx1536M -Xss1M -XX:+CMSClassUnloadingEnabled -XX:MaxPermSize=256M";
java $SBT_OPTS -jar `dirname $0`/sbt-launch.jar "$#"
EOF
echo "$sbt_text"
While your read command doesn't work as posted, not double-quoting $sbt_text will invariably perform word splitting (and also pathname expansion (globbing)), which, when passed to echo, means that any interior whitespace is normalized to a single space.
In order to preserve the value of a variable as-is in POSIX-like shells - without subjecting it to the shell expansions described above - you must double-quote it.
With respect to the read command, note that:
-r prevents usually unintended interpretation of \ instances in the input.
Prepending IFS= ensures that each line in the here-document is preserved as-is with respect to whitespace (no trimming of leading and trailing whitespace)
There's no need for a command substitution ($(...)) with cat, because << (a here-document) directly provides stdin input, which is where read takes its input from.
By using sbt_text=$(...) in your read command, you essentially made the output of the command substitution ($(...)) part of the (ultimately invalid) variable name rather than providing input, causing read to still wait for stdin input.
Using just assignment sbt_text=$(cat <<"EOF" ...) (without read) would almost have given you what you want (although at the expense of a call to external utility cat), except that the command substitution would have stripped any trailing newlines.

Answer 2

You should quote your variables:
echo "$sbt_text"
This prevents Bash from doing word splitting (and globbing, i.e. expanding wildcard characters like * and ?) after substituting your variable (parameter expansion). Note that setting IFS for read does not prevent word splitting on the echo command line. Try this for fun:
( IFS= ; echo $sbt_text )
vs.
IFS= echo $sbt_text ### won't work
The second example will not work - the subshell (( )) is necessary here because IFS is interpreted by the calling shell for word splitting in contrast to being interpreted by read in the question's code example.
Of course this works too (but "ruins" your IFS):
IFS= ; echo $sbt_text