CODEWITHSUNDEEP
shellunixfloating-pointsh
dead_jake
dead_jake

Reputation: 523

Subtracting two float variables and comparing shell script

I have two floating-point variables, time and prev_time, and I need to subtract them, and check if less than 0. I've looked up in dozens of forums, but can't seem to find an answer that works. I need to do something similar to:

if [[ `expr $time-$prev_time | bc` -lt 0 ]]

Any help is appreciated

Upvotes: 0

Views: 1012

Answers (1)

chepner
chepner

Reputation: 531758

From your use of [[ ... ]], I'll assume you are using bash. If you only care that the difference is less than 0, you only care that $time is less than $prev_time. You can split the floating point values into its integer parts, then compare them separately:

IFS=. read time_int time_frac <<< $time
IFS=. read prev_in prev_frac <<< $prev_time
if (( time_int < prev_int || (time_int == prev_int && time_frac < prev_frac) )); then

Or, you can use bc this way (plus, it's POSIX compliant):

if [ "$( echo "$time - $prev_time < 0" | bc )" = 1 ];

bc outputs 1 if the comparison is true, 0 if false.

Upvotes: 1

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