Read values into a shell variable from a pipe

I am trying to get bash to process data from stdin that gets piped into, but no luck. What I mean is none of the following work:

echo "hello world" | test=($(< /dev/stdin)); echo test=$test
test=

echo "hello world" | read test; echo test=$test
test=

echo "hello world" | test=`cat`; echo test=$test
test=

where I want the output to be test=hello world. I've tried putting "" quotes around "$test" that doesn't work either.

Use

IFS= read var << EOF
$(foo)
EOF

You can trick read into accepting from a pipe like this:

echo "hello world" | { read test; echo test=$test; }

or even write a function like this:

read_from_pipe() { read "$@" <&0; }

But there's no point - your variable assignments may not last! A pipeline may spawn a subshell, where the environment is inherited by value, not by reference. This is why read doesn't bother with input from a pipe - it's undefined.

FYI, http://www.etalabs.net/sh_tricks.html is a nifty collection of the cruft necessary to fight the oddities and incompatibilities of bourne shells, sh.

if you want to read in lots of data and work on each line separately you could use something like this:

cat myFile | while read x ; do echo $x ; done

if you want to split the lines up into multiple words you can use multiple variables in place of x like this:

cat myFile | while read x y ; do echo $y $x ; done

alternatively:

while read x y ; do echo $y $x ; done < myFile

But as soon as you start to want to do anything really clever with this sort of thing you're better going for some scripting language like perl where you could try something like this:

perl -ane 'print "$F[0]\n"' < myFile

There's a fairly steep learning curve with perl (or I guess any of these languages) but you'll find it a lot easier in the long run if you want to do anything but the simplest of scripts. I'd recommend the Perl Cookbook and, of course, The Perl Programming Language by Larry Wall et al.

This is another option

$ read test < <(echo hello world)

$ echo $test
hello world

read won't read from a pipe (or possibly the result is lost because the pipe creates a subshell). You can, however, use a here string in Bash:

$ read a b c <<< $(echo 1 2 3)
$ echo $a $b $c
1 2 3

But see @chepner's answer for information about lastpipe.

I'm no expert in Bash, but I wonder why this hasn't been proposed:

stdin=$(cat)

echo "$stdin"

One-liner proof that it works for me:

$ fortune | eval 'stdin=$(cat); echo "$stdin"'