BASH: how to perform arithmetic on numbers in a pipe

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 about it without breaking the pipe.

for example

> echo "1 2 3 4 5" | some command | cat 
1 4 9 16 25
>

Would you have any ideas on how to make something like this work? The actual operation I want to perform is sim开发者_StackOverflowply adding one to every number.

---

echo 1 2 3 4 5|{
  read line; 
  for i in $line;
  do
    echo -n "$((i * i)) "; 
  done; 
  echo
}

The {} creates a grouping. You could instead create a script for that.

---

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

---

Or..

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

---

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

---

echo 1 2 3 4 5 | xargs -n 1 bash -c 'echo $(($1*$1))' args 

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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

---

Or you can pipe to expression to bc:

echo "1 2 3 4 5" | (
  read line; 
  for i in $line;
  do
    echo $i^2 | bc; 
  done; 
  echo
)

---

If you prefer Python:

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

---

xargs, xargs, xargs

echo 1 2 3 4 5 | xargs -n1 echo | xargs -I NUMBER expr NUMBER \* NUMBER | xargs

Or, go parallel:

squareit () { expr $1 \* $1; }
export -f squareit
echo 1 2 3 4 5 | xargs -n1 | parallel --gnu squareit | xargs

Which would be way simpler if you passed your pipe as a standard set of args:

parallel --gnu "expr {} \* {}" ::: $(echo 1 2 3 4 5) | xargs

Or even:

parallel --gnu "expr {} \* {}" ::: 1 2 3 4 5 | xargs

Really worth taking a look at the examples in the doc: https://www.gnu.org/software/parallel/man.html

---

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 / /, $_'