Read values into a shell variable from a pipe

linux bash pipe
ldog picture ldog · Apr 30, 2010 · Viewed 328.7k times · Source

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.

Answer

yardena picture yardena · Jul 21, 2011

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.

Related questions

Split output of command by columns using Bash?

I want to do this: run a command capture the output select a line select a column of that line Just as an example, let's say I want to get the command name from a $PID (please note this is …

Read More
Pass a password to ssh in pure bash

I want to pass a password to ssh using a bash script (Yes, I know that there are ssh keys that I could use, but this is not what I intend). I found some solutions that were using expect but …

Read More
Example of using named pipes in Linux Bash

Can someone post a simple example of using named pipes in Bash in Linux?

Read More