Reputation: 41
So I have two files in my directory that contain a number in each of them. I want to make a script that calculates the average of these two numbers. How would I write it? Would this be correct?
avg=$((${<file1.txt}-${<file2.txt})/2)
Upvotes: 1
Views: 62
Reputation: 1525
Your example does not work. Furthermore, your formula is probably incorrect. Here are two options without unnecessary cat
:
avg=$(( (`<file1.txt` + `<file2.txt`) / 2 ))
or
avg=$(( ($(<file1.txt) + $(<file2.txt)) / 2 ))
I find the first one more readable though. Also be warned: this trivial approach will cause problems when your files contain more than just the plain numbers.
EDIT:
I should have noted that the first syntactical/legacy option which uses the backticks (` `) is no longer recommended and should be avoided. You can read more about the WHY here. Thanks at mklement0 for the link!
EDIT2:
According to Eric, the values are floating point numbers. You can't do this directly in bash because only integer numbers are supported. You have to use a little helper:
avg=$(bc <<< "( $(<file1.txt) + $(<file2.txt) ) / 2")
or maybe easier to understand
avg=$(echo "( $(<file1.txt) + $(<file2.txt) ) / 2" | bc)
For those who might wonder what bc
is (see man bc
):
bc is a language that supports arbitrary precision numbers with interactive execution of statements.
Here is another alternative since perl
is usually installed by default:
avg=$(perl -e 'print( ($ARGV[0] + $ARGV[1]) / 2 )' -- $(<file1.txt) $(<file2.txt))
Upvotes: 1
Reputation: 58998
You'll want to use a command substitution:
avg=$(($(cat file1.txt)-$(cat file2.txt)/2))
However, Bash is a pretty bad language for doing maths (at least unless it's completely integer maths). You might want to look into bc
or a "real" language like Python.
Upvotes: 0