BASH: how to perform arithmetic on numbers in a pipe

Question

I am getting a stream of numbers in a pipe, and would like to perform some operations before passing them on to the next section, but I\'m a little lost about how I would go

Answer 1

I'd write:

echo "1 2 3 4 5" | {
  for N in $(cat); do
    echo $((N ** 2))
  done | xargs
}

We can think of it as a "map" (functional programming). There are a lot of ways of writing a "map" function in bash (using stdin, function args, ...), for example:

map_stdin() {
  local FUNCTION=$1
  while read LINE; do
    $FUNCTION $LINE
  done
}

square() { echo "$(($1 * $1))"; }

$ echo "1 2 3 4 5" | xargs -n1 | map_stdin square | xargs
1 4 9 16 25

Answer 2

If you prefer Python:

#!/bin/python
num = input()
while num:
    print(int(num) + 1) # Whatever manipulation you want
    try:
        num = input()
    except EOFError:
        break

Answer 3

echo 1 2 3 4 5 | xargs -n 1 expr -1 +

Answer 4

Yoi might like something like this:

echo "1 2 3 4 5" | perl -ne 'print $_ ** 2, " " for split / /, $_'

or even like this:

echo "1 2 3 4 5" | perl -ne 'print join " ", map {$_ ** 2} split / /, $_'

Answer 5

Using awk is another solution, which also works with floats

echo "1 2 3 4 5" | xargs -n1 | awk '{print $1^2}' | xargs

or use a loop

for x in 1 2 3 4 5; do echo $((x**2)); done | xargs
for x in $(echo "1 2 3 4 5"); do echo $x^2 | bc; done | xargs # alternative solution
for x in $(seq 5); do python -c "print($x**2)"; done | xargs  # alternative solution but slower than the above
# or make it neat by defining a function to do basic math in bash, e.g.:
calc() { awk "BEGIN{print $*}"; } 
for x in $(seq 5); do calc $x^2; done | xargs

Answer 6

Or..

echo "1 2 3 4 5" | xargs -n 1 | while read number 
 do
   echo $((number * number))
 done