Write variables to a file which contains the variabe name and value

Question

I want to be able to read and write to a file with a bash script. I am able to read the variables from the file but I am not sure how to write to it.

The file data.txt contains the variable names and their values like this:

var1=2
var2=3

The shell script looks like this:

#!bin/bash

echo "Read"
var1=$(grep -Po "(?<=^var1=).*" data.txt)

echo "Do Something"
var2=${var1}

echo "Write"
# var2 should be saved in data.txt like this: var2=<Here is the Value>, e.g. var2=2

I can read the specific values of the variables with the grep command, which I got from this answer. But I am not sure how to implement the functionality to be able to save the values of the variables at the correct position (see the last comment in the bash script).
The variable names are unique in data.txt.

Any ideas how to achieve this?

echo "var2=$var2" > data.txt ? Is that what you are looking for ? — Aserre
– Aserre, Commented Mar 13, 2018 at 9:18
@Aserre Yes, but his instruction deletes the var1=2 in the data.txt. — Vuks
– Vuks, Commented Mar 13, 2018 at 9:24
@Aserre No need to get so harsh, I appreciate your effort and was just commenting about what happens. And the >> appends the line instead of replacing it. But neverless I found a solution and will post it in a second. Thanks for your input. :) — Vuks
– Vuks, Commented Mar 13, 2018 at 9:48

Vuks · Accepted Answer · 2018-03-13 09:52:13Z

1

I found a solution with the sed command:

echo "Write"
sed -i -e "s/$(grep -Po '(?<=^var2=).*' data.txt)/${var2}/g" data.txt

answered Mar 13, 2018 at 9:52

Vuks

8511 gold badge9 silver badges24 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

bigeast · Accepted Answer · 2018-03-13 09:46:11Z

0

You can use sed to do the job.

!/bin/bash

echo "Read"
var1=$(grep -Po "(?<=^var1=).*" data.txt)

echo "Do Something"
var2=${var1}

echo "Write"
sed -i "/var2/ s/.*/var2=${var2}/" data.txt # replace the line contains 'var2' with var2=2

I assume you use GNU sed, for BSD sed, you need to feed an extra suffix to -i.

answered Mar 13, 2018 at 9:46

bigeast

6375 silver badges14 bronze badges

2 Comments

Vuks Over a year ago

Sorry, I saw your answer after I posted mine. They are very similar, but yours doesn't replace the value but instead appends it to the existing value.

bigeast Over a year ago

Yes, it does. "/var2/ s/.*/var2=${var2}/" changed the whole line that contains "var2" into "var2=2", so now the "var2=3" will become "var2=2", which is exactly what you want.

Collectives™ on Stack Overflow

Write variables to a file which contains the variabe name and value

2 Answers 2

Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related