Truncated float number as variable filename in bash

Question

I wanted to do a for loop for all files with name "r?.???.txt", where ?.??? was a float from 0.000 to 3.999. However, bash does not have integer, as far as I know... That turns into a headache...

I tried to do for tedious for loop with two variables representing the numbers before and after decimal. However, I still need to insert zeros if you have ?.00?. Therefore I will need a proper treatment of float numbers and how to store / output them.

In summary, there are two questions I face

doing float in bash
output that float as a value and pass into filename

Thank you.

What's wrong with handling 2 integers? `for a in {0..3}; do for b in {000..999}; do echo "r$a.$b.txt"; done; done`. — gniourf_gniourf, Feb 14 '16 at 18:21

SLePort · Accepted Answer · 2016-02-14T18:35:06.153

1

Using 2 variables is a good idea.

You can keep the zero padding format with seq -f option :

#!/bin/bash
declare -i int=3;
declare -i dec=1000;

for i in $(seq 1 $int);do
        for j in $(seq -f "%03g" 1 $dec);
                do echo r$i.$j.txt;  # or do find . -name "r$i.$j.txt";
        done;
done;

edited Feb 14 '16 at 18:35

answered Feb 14 '16 at 18:28

SLePort

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score 0 · Answer 2 · edited May 23 '17 at 12:17

Answer 1) For float calculations you will have to delegate the task to other programs such as bc.

For example:

echo "scale=3;20.8/4 | bc 5.200

For more options you can check:

https://unix.stackexchange.com/questions/40786/how-to-do-integer-float-calculations-in-bash-or-other-languages-frameworks
https://unix.stackexchange.com/questions/76060/perform-floating-point-arithmetic-in-shell-script-variable-definitions
How do I use floating-point division in bash?

to find out filenames having float numbers you can use regular expressions along with find command:

$touch r3.987.txt $find . -regextype sed -regex ".*/r[0-9]\.[0-9]\{3\}.txt$" ./r3.987.txt

regular expression type is that of sed, find . means find in current directory

*/ => to check only for filenames only and skip the leading directory structure
[0-9] matches any digit in range 0 to 9
\. means match a dot
[0-9]\{3\} means [0-9]{3} to match exactly 3 digits and each digit can be in range 0-9
and finally ending in .txt

as for Answer 2) you can get that float value as a string by looping through the output of the find command

$for filename in "$(find . -regextype sed -regex ".*/r[0-9]\.[0-9]\{3\}.txt$")"  
> do  
> echo "Filename is $filename"  
> floatValueAsString=$(echo "$filename" | egrep -o '[0-9]\.[0-9]{3}')  
> echo "Float value as string is $floatValueAsString"  
> done  
Filename is ./r3.987.txt
Float value as string is 3.987

Truncated float number as variable filename in bash

2 Answers2