从 awk 输出构建数组

Question

Can anyone explain why the following doesn't work please?

list

the letter is d
the number is 4
the number is 2
the letter is g

script.sh

#!/bin/bash

cat "$1" | grep letter | array=($(awk '{print $4}'))

for i in "${array[@]}"
do
  :
  echo $i
done

If I run this bash script.sh list I expect the array to print d and g, but it doesn't. I think its because of how I am trying to set the array.

Answer 1

I think its because of how I am trying to set the array.

Each command in a pipeline | is run in a subshell - as a separate process. The parent process does not "see" variable changes from a child process.

Just:

array=($(grep letter "$1" | awk '{print $4}'))

or

array=($(awk '/letter/{print $4}' "$1"))

Run variable assignment in the parent shell.

Answer 2

You should assign the complete row of piped commands to a variable.

array=($(cat "$1" | grep letter | awk '{print $4}'))

The cat and grep command can be combined with awk , but why do you want an array?
I think you want the process each element in one loop, so first remove the double quotes:

for i in ${array[@]}
do
  :
  echo $i
done

Next, try to do this without an array

while read -r i; do
  :
  echo $i
done < <(awk '/letter/ {print $4}' "$1")