Extract substring from a field with single awk in AIX - awk

Question

I have a file file with content like:
stringa 8.0.1.2 stringx
stringb 12.01.0.0 stringx
I have to get a substring from field 2 (first two values with the dot).
I am currently doing cat file | awk '{print $2}' | awk -F. '{print $1"."$2}' and getting the expected output:
8.0
12.01
The query is how to do this with single awk?
I have tried with match() but not seeing an option for a back reference.
Any help would be appreciated.

Answer 1

You can do something like this.
$ awk '{ split($2,str,"."); print str[1]"."str[2] }' file
8.0
12.01
Also, keep in mind that your cat is not needed. Simply give the file directly to awk.

Answer 2

With GNU grep please try following command once.
grep -oP '^\S+\s+\K[[:digit:]]+\.[[:digit:]]+' Input_file
Explanation: Using GNU grep here. Using its -oP options to print matched part and enable PCRE with -P option here. In main program, matching from starting non-space characters followed by 1 or more spaces, then using \K option to forget that match. Then matching 1 or more digits occurrences followed by a dot; which is further followed by digits. If a match is found then it prints matched value.

Answer 3

I would use GNU AWK's split function as follow, let file.txt content be
stringa 8.0.1.2 stringx
stringb 12.01.0.0 stringx
then
awk '{split($2,arr,".");print arr[1]"."arr[2]}' file.txt
output
8.0
12.01
Explantion: split at . 2nd field and put elements into array arr.
(tested in gawk 4.2.1)

Answer 4

You could match digits . digits from the second column and print if there is a match:
awk 'match($2, /^[[:digit:]]+\.[[:digit:]]+/) {
print substr($2, RSTART, RLENGTH)
}
' file
Output
8.0
12.01

Answer 5

Also with GNU awk and gensub():
awk '{print gensub(/([[:digit:]]+[.][[:digit:]]+)(.*)/,"\\1","g",$2)}' file
8.0
12.01
gensub() provides the ability to specify components of a regexp in the replacement text using parentheses in the regexp to mark the components and then specifying \\n in the replacement text, where n is a digit from 1 to 9.

Answer 6

You should perhaps not use awk at all (or any other external program, for that matter) but rely on the field-splitting capabilities of the shell and some variable expansion. For instance:
# printf "%s\n%s\n" "stringa 8.0.1.2 stringx" \
"stringb 12.01.0.0 stringx" |\
while read first second third junk ; do
printf "=%s= =%s= =%s=\n" "$first" "$second" "$third"
done
=stringa= =8.0.1.2= =stringx=
=stringb= =12.01.0.0= =stringx=
As you can see the value is captured in the variable "$second" already and you just need to further isolate the parts you want to see - the first and second part separated by a dot. You can do that either with parameter expansion:
# variable="8.0.1.2"
# echo ${variable%.*.*}
8.0
or like this:
# variable="12.01.0.0"
# echo ${variable%${variable#*.*.}}
12.01
or you can use a further read-statement to separate the parts and then put them back together:
# variable="12.01.0.0"
# echo ${variable} | IFS=. read parta partb junk
# echo ${parta}.${partb}
12.01
So, putting all together:
# printf "%s\n%s\n" "stringa 8.0.1.2 stringx" \
"stringb 12.01.0.0 stringx" |\
while read first second third junk ; do
printf "%s\n" "$second" | IFS=. read parta partb junk
printf "%s.%s\n" "$parta" "$partb"
done
8.0
12.01