AIX Does not support bc boolean expression

Question

I ran into an issue where bc does not have boolean expressions in the AIX system. Wondering if there is a replacement command so I don't have make my code any longer? This is in a bash script.

Here is what I had:

percent=-0.17
max=0.20
if [[ $(bc <<< "$percent <= $max && $percent >= -$max") -ge 1 ]]; then
    echo "Under the $max acceptable buffer: File ACCEPTED" 
else
    echo "Over the $max acceptable buffer: File REJECTED"
    exit 1
fi

This is my output:

++ bc
syntax error on line 1 stdin
+ [[ '' -ge 1 ]]

Just curious, what would break if your code was a few bytes longer? — Jeff Schaller, Sep 17 '18 at 18:44
I’m comparing file size differences. We know how many bytes one line takes. So if there is too many lines in a file or too few we want to review that — Tags, Sep 17 '18 at 18:51
@JeffSchaller for the link you provide. Would it still work if it’s a bash shell? Sorry I’m a bit new to scripting. — Tags, Sep 17 '18 at 19:10
many shells won't do floating point math, so awk is the usual answer here — Jeff Schaller, Sep 17 '18 at 19:31
I ended up using awk. It just gave me more control over the range. This was from @JeffSchaller link — Tags, Sep 17 '18 at 23:17

score 3 · Accepted Answer · answered Sep 17 '18 at 19:37

3

bc's POSIX spec does not require bare conditionals, and AIX's bc does not support them. You would have to break out the test like this:

percent=-0.17
max=0.20
if [[ $(bc <<< "if ($percent <= $max) if ($percent >= -$max) 1") -eq 1 ]]; then
    echo "Under the $max acceptable buffer: File ACCEPTED" 
else
    echo "Over the $max acceptable buffer: File REJECTED"
    exit 1
fi

Re-formatting the bc script, it looks like this:

if ($percent <= $max) 
  if ($percent >= -$max) 
    1

... only if the $percent value is within both ranges does the expression 1 get executed, which prints 1 to stdout.

answered Sep 17 '18 at 19:37

Jeff Schaller

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I see what you did here. But if floats are working in the if statements this should work by just comparing the two numbers directly? – Tags Sep 17 '18 at 20:04
@Tags, bash arithmetic is integer-only at this point; ksh93 supports floating point. See also: https://unix.stackexchange.com/questions/40786/how-to-do-integer-float-calculations-in-bash-or-other-languages-frameworks. So you need to be careful with the shell, or use a utility that supports it. – Jeff Schaller Sep 17 '18 at 20:10
I see. Thanks and this works perfectly. I just didnt like that a null is passed but that was an easy modification – Tags Sep 17 '18 at 20:17

AIX Does not support bc boolean expression

1 Answers1