Extract substrings from a file and store them in shell variables - linux

Question

I am working on a script. I have a file called test.txt whose contents are as follows:
a. parent = 192.168.1.2
b. child1 = 192.168.1.21
c. child2 = 192.154.1.2
I need to store the values in three different variables called parent, child1and child2 as follows and then my script will use these values:
parent = 192.168.1.2
child1= 192.168.1.21
child2= 192.154.1.2
How can I do that using sed or awk? I know there is a way to extract substrings using awk function substr but my particular requirement is tostore them in variables as mentioned above. Thanks

Answer 1

Try this if you're using bash:
$ declare $(awk '{print $2"="$4}' file)
$ echo "$parent"
192.168.1.2
If the file contained white space in the values you want to init the variables with then you'd just have to set IFS to a newline before invoking declare, e.g. (simplified the input file to highlight the important part of white space on the right of the = signs):
$ cat file
parent=192.168.1.2 is first
child1=192.168.1.21 comes after it
child2=and then theres 192.154.1.2
$ IFS=$'\n'; declare $(awk -F'=' '{print $1"="$2}' file)
$ echo "$parent"
192.168.1.2 is first
$ echo "$child1"
192.168.1.21 comes after it

Answer 2

Ed Morton's answer is the way to go for the specific problem at hand - elegant and concise.
Update: Ed has since updated his answer to also provide a solution that correctly deals with variable value values with embedded spaces - the original lack of which prompted this answer.
His solution is superior to this one - more concise and more efficient (the only caveat is that you may have to restore the previous $IFS value afterward).
This solution may still be of interest if you need to process variable definitions one by one, e.g., in order to transform variable values based on other shell functions or variables before assigning them.
The following uses bash with process substitution on a simplified problem to process variable definitions one by one:
#!/usr/bin/env bash
while read -r name val; do # read a name-value pair
# Assign the value after applying a transformation to it; e.g.:
# 'value of' -> 'value:'
declare $name="${val/ of /: }" # `declare "$name=${val/ of /: }"` would work too.
done < <(awk -F= '{print $1, $2}' <<<$'v1=value of v1\nv2= value of v2')
echo "v1=[$v1], v2=[$v2]" # -> 'v1=[value: v1], v2=[value: v2]'
awk's output lines are read line by line, split into name and value, and declared as shell variables individually.
Since read, which trims by whitespace, is only given 2 variable names to read into, the 2nd one receives everything from the 2nd token _through the end of the line, thus preserving interior whitespace (and, as written, will trim leading and trailing whitespace in the process).
Note that declare normally does not require a variable reference on the RHS of the assignment (the value) to be double-quoted (e.g. a=$b; though it never hurts). In this particular case, however - seemingly because the LHS (the name) is also a variable reference - the double quotes are needed.

Answer 3

I also got it done finally . Thanks everyone for helping.
counter=0
while read line
do
declare $(echo $line | awk '{print $2"="$4}')
#echo "$parent"
if [ $counter = 0 ]
then
parent=$(echo $parent)
fi
if [ $counter = 1 ]
then
child1=$(echo $child)
else
child2=$(echo $child)
fi
counter=$((counter+1))
done < "/etc/cluster_info.txt"

Answer 4

eval "$( sed 's/..//;s/ *//g' YourFile )"
just a sed equivalent to Ed solution and with an eval instead of declare.