单行命令从bash中的文件中复制

Question

As the title suggest, but is it possible to multiply two numbers together by reading in from a file using arithmetic expansion using only the commands echo or cat ? i know you can do this through piping with the use of bc but i was looking to do something a little different. So say we have a text file

Text File

12*9
2*3

and using cat multiply.txt | bc cat multiply.txt | bc but changing it so that it doesnt require the use of bc but instead reads in the file and does the math on its own without the use of bc and with the use of arithmetic expansion instead?

Answer 1

You don't need cat either

for a in $(< test.txt); do echo "$(($a))" ; done

or

while read -r a; do echo "$(($a))"; done < test.txt

which would handle better spaces and other chars in the file

Answer 2

It can be done like this (later learned it's not the right way , read comments below)

for a in $(cat test.txt); do echo "$(($a))" ; done

Result:

108
6

With only cat and echo it could be done like this but the number of lines in the file should be known beforehand and the array creation could fail for the same reason the for could.

a=( $(cat test.txt) ); echo "$((${a[0]}))" ; echo "$((${a[1]}))"

108
6