Floating point results in Bash integer division

I have a backup script on my server which does cron jobs of backups, and sends me a summary of files backed up, including the size of the new backup file. As part of the script, I'd like to divide the final size of the file by (1024^3) to get the file size in GB, from the file size in bytes. Since bash does not have floating point calculation, I am trying to use pipes to bc to get the result, however I'm getting stumped on basic examples. I tried to get the value of Pi to a scale, however, even though the following works: ``` ~ #bc -l bc 1.06.95 Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006 Free Software Foundation, Inc. This is free software with ABSOLUTELY NO WARRANTY. For details type `warranty'. 4/3 1.33333333333333333333 22/7 3.14285714285714285714 q 0 quit ``` A non interactive version does not work: ``` #echo $(( 22/7 )) | bc 3 ``` This works: ``` #echo '22/7' | bc -l 3.14285714285714285714 ``` But I need to use variables. So it doesnt help that the following does not work: ``` #a=22 ; b=7 #echo $(( a/b )) | bc -l 3 ``` I'm obviously missing something in the syntax for using variables in Bash, and could use with some 'pointers' on what I've misunderstood. As DigitalRoss said, I can use the following: ``` #echo $a / $b | bc -l 3.14285714285714285714 ``` However I cant use complex expressions like: ``` #echo $a / (( $b-34 )) | bc -l -bash: syntax error near unexpected token `(' #echo $a / (( b-34 )) | bc -l -bash: syntax error near unexpected token `(' #echo $a / (( b-34 )) | bc -l -bash: syntax error near unexpected token `(' ``` Can someone give me a working correct syntax for getting floating point results with complicated arithmetic expresssions?