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J. Doe
Asked: 2018-06-07 10:04:54 +0800 CST

How to move decimal point in bash

  • 772

I have a variable that is stored as "1.20E20". I would like for it to be changed to "0.0120E22". Is there a simple command to change this value? I tried 

let nh=$nh/100

But that did not work; I assume it is because of the character value in the variable. I know there are various solutions; what is the best way to solve this?

bash

2 Answers

  1. Best Answer

    I don't know of a way to force printf to shift the exponent. Let's do it manually: multiply the coefficient by 10-2, and add 2 to the exponent.

    n=1.20E20
m=2
IFS="E" read coeff exp <<<"$n"
new=$(printf "%.4fE%d\n" "$(echo "$coeff * 10^-($m)" | bc -l)" "$((exp+m))")
# => 0.0120E22

    We can validate with:

    $ printf "%e\n" "$new"
1.200000e+20
    • 6

  2. I’d write a simple bash script like this:

    #!/bin/bash
a=${1%E*}
b=${1#*E}
echo 0$(<<<"scale=4;$a/10^$2" bc)E$((b+$2))

    You just need to give it the values as arguments, first the number and then the shift:

    $ bash /path/to/script 1.20E20 2
0.0120E22
  # or, as a oneliner:
$ bash -c 'echo 0$(<<<"scale=4;${1%E*}/10^$2" bc)E$((${1#*E}+$2))' _ 1.20E20 2
0.0120E22
    • 2