версия,число +1

awk -F= '{if ($1=="betaver") {print $1"="$2+1} else {print $0}}'

$ betaver=8; awk -F= '{if ($1=="$betaver") {print $1"="$2+1} else {print $0}}'; echo $betaver
^C
$ betaver=8; awk -F= '{if ($1=="betaver") {print $1"="$2+1} else {print $0}}'; echo $betaver
^C

awk -F= -vOFS== '($1 == "betaver") { $2++ } 1'

$ cat ABUILD | grep betaver=
betaver=9
$ awk -F= '{if ($1==«betaver») {print $1"=«$2+1} else {print $0}}' ./ABUILD 
awk: {if ($1==«betaver») {print $1"=«$2+1} else {print $0}}
awk:          ^ invalid char '�' in expression

b=`cat ABUILD | grep betaver= | sed s/betaver=//`; echo $b; let "n=$b+1"; echo $n; sed "/^betaver=/s|$b|$n|" ABUILD | grep "betaver="
9
10
betaver=10

$ cat >ABUILD <<EOF
> alphaver=1
> betaver=2
> gammaver=3
> EOF
$ awk -F= -vOFS== '$1 == "betaver" { $2++ } 1' ABUILD > ABUILD.new
$ mv ABUILD{.new,}
$ cat ABUILD
alphaver=1
betaver=3
gammaver=3

$ a=9
$ b="betaver="$a
$ echo $b
betaver=9
$ a=$((a+1))
$ b="betaver="$a
$ echo $b
betaver=10

[ megabaks@desktop ] ~ $ echo "betaver=9" > test_file
[ megabaks@desktop ] ~ $ export "$(grep "^betaver=" test_file)"
[ megabaks@desktop ] ~ $ sed "s|betaver=${betaver}|betaver=$(( ${betaver} + 1  ))|" -i test_file 
[ megabaks@desktop ] ~ $ cat test_file 
betaver=10
[ megabaks@desktop ] ~ $