evaluate arithmetic expression passed as argument in awk - awk

Question

How to evaluate arithmetic expression passed as argument in awk?
I have this in a file.
1*2*3
1+2*3
awk should output 6, 7, when this file is passed in.

Answer 1

awk(1) is the wrong tool as it doesn't have an eval() function. I suggest modifying the file into input for bc(1) or using shell arithmetic expansion:
while read expr; do
echo "$(($expr))"
done < file

Answer 2

awk doesn't have eval() funciton
use bc or shell arithmetic expansion both can make it
But, if you use it in hadoop scripts, consider the subprocesses problem
besides, you can try these ways:
Consider to write an expression evaluator in AWK (from archive.org, search for calc3)
Use eval
Use Python's eval function

Answer 3

I know this is awful but we can:
awk '{system(sprintf("awk \"BEGIN {print " $0 "}\""))}'
as pointed out, bc, Python eval, bash $(( )), are better solutions
One last suggestion Perl:
perl -nE 'say eval'

Answer 4

Here's another hack inspired in part by #JJoao's answer, and feedback from #DracoMetallium of Twitter...
#!/usr/bin/env bash
calc() {
awk 'BEGIN { print '"${#//inf/(2 ** 1024)}"'; }'
}
calc '1/2'
#> 0.5
... this also handles instances of inf being passed via Bash built-ins for search-and-replace, eg...
calc 'inf + inf'
#> inf
calc '-inf + -inf'
#> -inf
calc '-inf + inf'
#> -nan
Which may be useful within one's .bashrc file for quick command-line based calculations.
And for completeness, here's an example how to preform the above in (mostly) pure Awk...
calc.awk
#!/usr/bin/awk -f
function calc(expression) {
gsub("inf", "(2 ** 1024)", expression)
system(sprintf("awk \"BEGIN {printf(" expression ")}\""))
}
{
print calc($0)
}
... as well as examples of usage...
calc.awk <<<'1 /2'
#> 0.5
printf '2*2\nsqrt(9)\n' | calc.awk
#> 4
#> 3
calc.awk <<'EOF'
22 / 7
(1 + sqrt(5)) / 2
EOF
#> 3.14286
#> 1.61803
tee -a 'input-file.txt' 1>'/dev/null' <<'EOF'
1*2*3
1+2*3
EOF
calc.awk input-file.txt
#> 6
#> 7

Answer 5

awk code self-eval :
echo '1*2*3
1+2*3' |
mawk '
function eval(_,__,___) {
return substr("",
(___=RS)*(RS="^$")*((__="mawk \47BEGIN { "\
"printf(\"%.f\","(_)") }\47")|getline _),
close(__)^(RS=___)*__)_
}
$++NF = eval($!_)'
1*2*3 6
1+2*3 7
And have non-GMP-enabled variants of awk handle bigints via gawk-gmp :
echo '9^357' | mawk2 '
function eval(__,_,___) {
return substr("",(___=RS) * (RS="^$") * ((_="gawk -Mbe"\
" \47BEGIN { printf("(__)") }\47")|getline __), close(_)^(RS=___)*_)__
} $++NF = eval($!_)'
9^357 46192968246584020379055552051071189505164865440669900464
39030285864012137741835863345354556100224446056419891013
64348709024164571890111337972631022968123699490725498380
48619487796915547325757427881925121757649463471671577403
93732287476951829673979533419257547784348206387576562750
0451665854873600139914343339972692154903156749530623670508969

Answer 6

As an example, consider what iftop gives you:
Host name last 2s last 10s last 40s cumulative
1 10.150.1.1 => 650B 533B 533B 2.08KB
85.239.108.20 <= 16.0KB 12.9KB 12.9KB 51.5KB
Let's say you need the 2 up/down lines into one line and calculate KB/B into right byte values (*1024). You could have this:
iftop -i eth1 -ts 10 -Bn|egrep "<|>"| sed 's/^ //g;s/^[1-9]/x/g;s/KB/ 1024/g;s/B/ 1/g' | tr -d '\n'|tr "x" '\n'| grep .| awk '{print $1" "$11" - "$9*$10+$19*$20" "$9*$10" "$19*$20 }'