How to assign command output to variables with bash and read [duplicate]

Question

I'm trying to assign the output of a command to multiple variables, one per output "word". Doing (bash on linux)

echo foo bar baz | read FOO BAR BAZ
echo $FOO $BAR $BAZ

shows only empty strings. Doing

read FOO BAR BAZ < <(echo foo bar barz)
echo $FOO $BAR $BAZ

works as expected. What's wrong here? I thought using a pipe was the most obvious and right way to do that.

Pipes create shubshells which cannot alter the non-subshell environment. I'll link a duplicate with answers in a minute. — Socowi
– Socowi, Commented Jul 22, 2019 at 10:46
Since you already have a working code I guess you just want an explanation of what is hapenning. User pbhd nicely explains it in his post. Piped operations happen in a subshell and therefore any declared variables are accessible only inside it. — Simon Kocurek
– Simon Kocurek, Commented Jul 22, 2019 at 10:48
This answer explains the problem but is on unix SE. When someone finds a good duplicate on StackOVerflow please link it. I'm sure there is one. — Socowi
– Socowi, Commented Jul 22, 2019 at 10:49

Mihir Luthra · Accepted Answer · 2019-07-22 12:51:53Z

4

echo foo bar baz | read FOO BAR BAZ
echo $FOO $BAR $BAZ

In this case it prints nothing. The reason is because pipe creates a subshell in which FOO, BAR and BAZ get values.

echo foo bar baz | { read FOO BAR BAZ ;  echo $FOO $BAR $BAZ ;}

Try this, it will print correct value of all variables. Here, the braces encapsulated the echo command to run in the same subshell in which the variables are read.

read FOO BAR BAZ < <(echo foo bar barz)
echo $FOO $BAR $BAZ

In this case everything happens in the same shell, so you see the output you expect.

answered Jul 22, 2019 at 12:51

Mihir Luthra

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Paul Hodges · Accepted Answer · 2019-07-22 13:34:53Z

1

One addition to Mihir's answer -

read a b c <<< "$( echo 1 2 3 )" # a here-string

answered Jul 22, 2019 at 13:34

Paul Hodges

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