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Full Discussion: Using read to assign value to bash variable not working
Top Forums UNIX for Beginners Questions & Answers Using read to assign value to bash variable not working Post 303043533 by Chubler_XL on Thursday 30th of January 2020 09:04:36 PM
Old 01-30-2020
This is because commands within a pipeline are run in subshells so the read statement is setting the variables is a subshell which has not impact on the main shell.

You can achieve what you want using process substitution like this:

Code:
# read var1 var2 < <(openstack hypervisor stats show | awk -F'|' 'NR==14{print $2,$3}')
# echo $var1
vcpus

Edit:
Also in bash 4.* and later you can use a shell option to run the last pipeline command in the current shell.
Note this only work for shells without job control, so in an interactive shell (as opposed to a script) you will also need turn off job control (set +m).

Quote:
lastpipe
If set, and job control is not active, the shell runs the last command of a pipeline
not executed in the background in the current shell environment.
Code:
# echo $BASH_VERSION
5.0.7(1)-release
# shopt -s lastpipe
# set +m

# echo A B C | head -1 | read first second rest
# echo $first
A

# set -m
# shopt -u lastpipe

Last edited by Chubler_XL; 01-30-2020 at 10:25 PM..
These 2 Users Gave Thanks to Chubler_XL For This Post:
MadeInGermany sand1234
 

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LEARN ABOUT DEBIAN

mstack

VIEW-OS(1)						      General Commands Manual							VIEW-OS(1)

NAME

       mstack - networking stack selection

SYNOPSIS

       mstack [-hv] [-o protocol list] stack_mountpoint command

DESCRIPTION

       In  View-OS  multiple  networking  stacks are available to processes at the same time. View-OS supports the msocket(2) system call.  mstack
       defines the default stack (for each address family) that is used when msocket refers to a NULL pathname for  its  stack.   mstack  provides
       also a backward compatibility for all the programs using the obsolete socket(2) system call.  The stack mountpoint identifies the stack. In
       ViewOS it is the mountpoint where the stack was mounted (by mount(2)(8).  In fact the call:
       "socket(domain,type,protocol)"
       is equivalent to:
       "msocket(NULL,domain,type protocol)"
       mstacks changes the default stack for the desired protocol families and executes the command (by execve(2)).

OPTIONS

       -h  prints the mstack command usage

       -v  sets the verbose mode on

       -o  defines the list of protocols. Without a -o option, mstack redefines the default stack for all protocols families.  The list of  proto-
	   cols  may  include  the  a  comma  separated sequence of the following items: all, unix (or simply u), ipv4 (4), ipv6 (6), netlink (n),
	   packet (p), bluetooth (b), irda (i), ip (which include all ip related protocols ipv4, ipv6, netlink and packet), #n where n is the num-
	   ber	of protocol.  Each item can be prefixed by + or - to specify whether the protocol/group of protocols must be added or removed from
	   the set.

EXAMPLES

       mstack /dev/net/lwip ip addr
	      lists the address managed by the stack mounted on /dev/net/lwip.

       exec mstack /dev/net/null bash
	      disables the standard stack in a new bash (which overcomes the current one).

       mstack -o ip /dev/net/lwip bash
	      starts a new bash which uses the stack /dev/net/lwip for ipv4 and ipv6 but not for the other protocols.

       mstack -o -unix /dev/net/lwip bash
	      starts a new bash which uses the stack /dev/net/lwip for all protocols but AF_UNIX.

       mstack -o +ip,-ipv6 /dev/net/lwip bash
	      starts a new bash which uses the stack /dev/net/lwip for ipv4, netlink, packet but not ipv6.

SEE ALSO

       umview(1), kmview(1), msocket(3), umnetnative(9), umnetnull(9), umnetlwipv6(9), unix(7), ip(7), ipv6(7), netlink(7), packet(7).

AUTHORS

       View-OS is a project of the Computer Science Department, University of Bologna. Project Leader: Renzo Davoli.
       <http://www.sourceforge.net/projects/view-os>

       Howto's and further information can be found on the project wiki <wiki.virtualsquare.org>.

VIEW-OS: a process with a view					  April 23, 2008							VIEW-OS(1)
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