Basically, I need to extract disk capacity from the data center description which basically has a numeric value preceding the unit of measure like GB
... 
echo $x | sed "s/^[^0-9]*\([0-9]*[.]*[0-9]*\)[^0-9A-Z]*GB.*/\1/g"

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Why so complicated? This should do: 

echo $x | sed "s/.\+ \([0-9]\+\)GB.*/\1/g"

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But as LanX says, sed(1) doesn't use PCRE. Read perlrun and perlre to understand the following:

echo $x | perl -ple 's/.+?(\d+)\s?GB.*/$1/'

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perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'

In reply to Re: Regex help! by shmem
in thread Regex help! by lpanokarren

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