· df · 1 min read
Arithmetic/Math calculations using shell script & Perl
Unix Shell scripts are perfect when it comes to simple automation tasks. But the in-built calculations are quite poor compared to rest of its functionality. The main issues I've faced using out-of-box shell script functions like expr, bc, echo are
Object Oriented programs like Java/Python/.NET are excellent for arithmetic calculations. But this involves another level of coding and program installation. The trick I used is to use PERL which is built in almost all *nix distributions. Some of the advantages of using PERL within shell script are
The above calculation will subtrace $VAL1 from $VAL2 and print with no decimal places (0f). The precision can be easily manipulated by changing the printf
- Unable to calculate decimal places correctly
- Error handling very poor (even divide by 0) and goes out of control.
- Hard to control precision
- Escape characters and regex increases complexity with formula
Object Oriented programs like Java/Python/.NET are excellent for arithmetic calculations. But this involves another level of coding and program installation. The trick I used is to use PERL which is built in almost all *nix distributions. Some of the advantages of using PERL within shell script are
- Easy to embed Perl commands into shell scripts
- Most of *nix distro have PERL inbuilt
- Reduced regex or escape character usage
- Can put formulae into config file and can loop them into the shell script
- precision, error handling are much better
How to do math calculations in shell scripts
- Write your shell script and put a function to do the real formula calculation
- Use perl command line (-e) within shell script
perl -le 'printf "%.0f", eval"@ARGV"' "($VAL2-$VAL1)"
The above calculation will subtrace $VAL1 from $VAL2 and print with no decimal places (0f). The precision can be easily manipulated by changing the printf