CODEWITHSUNDEEP
bashshell
user1754439
user1754439

Reputation: 61

Variable disappear after quitting the while loop

I know this question has been answered so many times. However, I still have some points need to be clarified. First let me paste my code snippet:

  1 #!/bin/bash
  2 declare -a test
  3 declare -i counter
  4
  5 while read x;
  6 do
  7   test[counter]=$x
  9   ((counter++))
 10 done < reg.txt
 11 echo "---------------------"
 12 echo ${test[0]}
 13 echo ${test[1]}

And the data in reg.txt is 

  1.1.1.1
  2.2.5.6
  45.25.12.45
  1.1.2.3
  1.1.3.4

I know that to put data in array test properly, I have to use '<' to turn file "reg.txt" into input data. However, how am I supposed to pick out ip address contains "1.1".

At line 10, I tried different things such as:

 done < reg.txt|grep "1.1" #Using this way makes the 'test' array empty.

Or this:

 done < <(reg.txt | grep "1.1")

The grammar is incorrect. (A lot of people suggest this and I don't know why).

In summary, I mean, is there a way to re-construct file before being read by while loop?

Upvotes: 2

Views: 231

Answers (1)

ewindes
ewindes

Reputation: 810

Using this syntax: 

done < reg.txt|grep "1.1"

doesn't do what you want it to do; instead, it applies the grep command to the output of the while loop.

The test array is does get populated with 5 values, but those values aren't remembered after the while loop completes - as explained in the answers to this question: Modifying a variable inside while loop is not remembered

What you're looking for is this:

done < <(cat reg.txt | grep "1\.1")

Note that the part within the parenthesis is a pipeline, and it needs to be a valid bash command. (You were missing the "cat" command.) You can test that part separately and verify that it selects the input data that you want.

Upvotes: 1

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