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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:
 

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read(1) 						      General Commands Manual							   read(1)

NAME
read - read a line from standard input SYNOPSIS
var ... DESCRIPTION
reads a single line from standard input. The line is split into fields as when processed by the shell (refer to shells in the first field is assigned to the first variable var, the second field to the second variable var, and so forth. If there are more fields than there are specified var operands, the remaining fields and their intervening separators are assigned to the last var. If there are more vars than fields, the remaining vars are set to empty strings. The setting of variables specified by the var operands affect the current shell execution environment. Standard input to can be redirected from a text file. Since affects the current shell execution environment, it is usually provided as a normal shell special (built-in) command. Thus, if it is called in a subshell or separate utility execution environment similar to the following, it does not affect the shell variables in the caller's environment: Options recognizes the following options: Do not treat a backslash character in any special way. Consider each backslash to be part of the input line. Opperands recognizes the following operands: var The name of an existing or nonexisting shell variable. EXTERNAL INFLUENCES
Environment Variables determines the internal field separators used to delimit fields. RETURN VALUE
exits with one of the following values: 0 Successful completion. >0 End-of-file was detected or an error occurred. EXAMPLES
Print a file with the first field of each line moved to the end of the line. while read -r xx yy do printf "%s %s " "$yy" "$xx" done < input_file SEE ALSO
csh(1), ksh(1), sh(1), sh-posix(1). STANDARDS CONFORMANCE
read(1)
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