markdown shell I / O.

Posted 2021-05-05

#### Reading from more than one file at a time
[linux - Looping through the content of a file in Bash - Stack Overflow](https://stackoverflow.com/questions/1521462/looping-through-the-content-of-a-file-in-bash)
```shell
while read -u 3 -r line1 && read -u 4 -r line2; do
  # process the lines
  # note that the loop will end when we reach EOF on either of the files, because of the `&&`
done 3< input1.txt 4< input2.txt
```

##### Reading a whole file into an array (Bash versions 4x and later)
```shell
readarray -t my_array < my_file

for line in "${my_array[@]}"; do
  # process the lines
done
 
```