Multiply all values in txt file in bash

Question

I have a file that I need to multiply each number with -1. I have tried some commands but the result I get every time is only the first column multiplied with -1. Please help!

The file is as follows:

-1 2 3 -4 5 -6
7 -8 9 10 12 0

The expected output would be

1 -2 -3 4 -5 6
-7 8 -9 -10 -12 0

Commands I have tried are:

awk '{print $0*-1}' file
sed 's/$/ -1*p /' file  | bc (syntax error)
sed 's/$/ * -1 /' file  | bc (syntax error)
numfmt --from-unit=-1 < file (error: numfmt: invalid unit size: ‘-1’)

Answer 1

With bash and an array:

while read -r -a arr; do
  declare -ia 'arr_multiplied=( "${arr[@]/%/*-1}" )';
  echo "${arr_multiplied[*]}";
done < file

Output:

1 -2 -3 4 -5 6
-7 8 -9 -10 -12 0

I got this idea from this Stack Overflow answer by j4x.

Answer 2

One awk approach:

$ awk '{for (i=1;i<=NF;i++) $i=$i*-1} 1' file
1 -2 -3 4 -5 6
-7 8 -9 -10 -12 0

Using the <var_or_field><op>=<value> construct:

$ awk '{for (i=1;i<=NF;i++) $i*=-1} 1' file
1 -2 -3 4 -5 6
-7 8 -9 -10 -12 0

Answer 3

Using perl and its autosplit mode:

perl -lane 'print join(" ", map { $_ * -1 } @F)' file

Answer 4

To multiply every number in the file with -1, you can use the following 'awk'command:

   `awk '{ for (i=1; i<=NF; i++) $i=$i*-1; print }' file`

This command reads each line of the file, and for each field (number) in the line, it multiplies it by -1. It then prints the modified line.

The output will be as follows:

    1 -2 -3 4 -5 6
    -7 8 -9 -10 -12 0

Alternatively, you can use the following 'sed' command:

   sed 's/-\([0-9]*\)/\1/g; s/\([0-9]*\)/-\1/g' file

This command replaces all negative numbers with their positive equivalent, and all positive numbers with their negative equivalent. The output will be the same as above.

Answer 5

For completeness an approach with ruby.

• -l Line-ending processing
• -a Auto-splitting, provides $F (field, set with -F)
• -p Auto-prints $_ (line)
• -e Execute code

ruby -lape '$_ = $F.map {|x| x.to_i * -1}.join " "' file
1 -2 -3 4 -5 6
-7 8 -9 -10 -12 0

Answer 6

Just switching the signs ought to do.

$: cat file
1 -2 -3 4 -5 6
-7 8 -9 -10 -12 0

$: sed 's/^ */ /; s/  */  /g; s/  -/ /g; s/  / -/g; s/-0/0/g; s/^ *//;' file
-1 2 3 -4 5 -6
7 -8 9 10 12 0

If you don't care about leading spaces or signs on your zeros, you can drop some of that. The logic is flexible, too...

$: sed 's/ *-/+/g; s/ / -/g; s/+/ /g;' x
1 2 3 -4 5 -6
 7 -8 9 10 12 -0

Answer 7

There are multiple ways we can do this. I can think of the following 2 ways

cat file | awk '{for (i=1;i<=NF;i++){ $i*=-1} print}'

This will give out

1 -2 -3 4 -5 6
-7 8 -9 -10 -12 0

In this method we overwrite the $i value and print $0

Another way

cat random.xml | awk '{for (i=1;i<=NF;i++){printf("%d ",$i*-1)} printf("\n")  }'

Gives the output

1 -2 -3 4 -5 6
-7 8 -9 -10 -12 0

In this method we print the value $i*-1 and so we need to use printf() function

Answer 8

don't "do math" and actually multiply by -1 -

just use regex to flip the signs, and process thousands or even millions of numbers with 3 calls to gsub()