[Help-bash] something about bc

[lina]

Hi,

I tried but still don't know how to achieve it with *bc*

some wrong try:

$ a=1.5 ; a+=1 ; echo $a
1.51

$ a=1.5 ; a+=1 | bc; echo $a
1.5

$ a=1.5 ; let "a+=1" | bc; echo $a
bash: let: 1.5: syntax error: invalid arithmetic operator (error token 
is ".5")
1.5

Thanks with best regards,