Grep – Useful expressions

Grep file size from du -sh
Format (10K , 10.1M , 1000.21G)

grep -oE "^[[:digit:]]+(\.[[:digit:]]+)?[KMG]"

Or

grep -oE "^[[:digit:]]+(\.[[:digit:]]+)?[KMG]|^[[:digit:]]+[[:blank:]]"

Grep IP address

grep -E '(^|[[:blank:]])[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}([[:blank:]]|$)' | sed -e 's/[[:blank:]]//g'
# grep sed awk
grep -E '(^|[[:blank:]])[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}([[:blank:]]|$)' | sed -e 's/[[:blank:]]//g' | awk -F"." '{ if ($1 <= 255 && $2 <= 255 && $3 <= 255 && $4 <= 255) print $1"."$2"."$3"."$4}'

Grep upper or lower character

# grep any upper character and lower 'a'
grep -E '[[:upper:]a]'
# grep upper of lower single alphabet (defined by variable)
(alpha=a;Alpha=`echo ${alpha} | tr [a-z] [A-Z]` ; echo aABab | grep -E '[${alpha}${Alpha}]')