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decrement a four part number in shell script

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# 1  
Old 12-29-2009
decrement a four part number in shell script
I have a four part number

eg: 1.21.1.3

I need to find a way in shell script to decrement this by one and put in a loop

so the values printed will be

1.21.1.2
1.21.1.1
1.21.1.0

Which is the best way to do this in shell script??
# 2  
Old 12-29-2009
Code as below...you can let x be read by while loop from a file.


Code:
x=1.21.1.4
y=${x##[0-9]*.}
while  [[ ${y} -ge  0 ]]
do
echo ${x%.[0-9]*}.${y}
(( y-- ))
done

Code:
o/p:-
1.21.1.4
1.21.1.3
1.21.1.2
1.21.1.1
1.21.1.0

SmilieSmilieSmilieSmilieSmilie

---------- Post updated at 10:13 ---------- Previous update was at 10:01 ----------

I mean in above that if you have
a file like below:-

Code:
cat file.txt:-
1.2.3.4
2.3.4.5
3.4.5.6
.
.
.


Just add another while loop to read
the value of x :-

New code:-


Code:
while read x
do
y=${x##[0-9]*.}
while  [[ ${y} -ge  0 ]]
do
echo "${x%.[0-9]*}"".""${y}"
(( y-- ))
done
done < file.txt



Code:
o/p:-
1.2.3.4
1.2.3.3
1.2.3.2
1.2.3.1
1.2.3.0
2.3.4.5
2.3.4.4
2.3.4.3
2.3.4.2
2.3.4.1
2.3.4.0
3.4.5.6
3.4.5.5
3.4.5.4
3.4.5.3
3.4.5.2
3.4.5.1
3.4.5.0


SmilieSmilieSmilieSmilie
# 3  
Old 12-29-2009
awk 'BEGIN{FS=".";} {if($4 >0){ while(x>=0) {x=$4--;print $1"."$2"."$3"."x;}}' filename

#filename has the IPs to be printed
# 4  
Old 12-29-2009
Quote:
Originally Posted by ahmad.diab
Code as below...you can let x be read by while loop from a file.

Code:
x=1.21.1.4
y=${x##[0-9]*.}
while  [[ ${y} -ge  0 ]]
do
echo ${x%.[0-9]*}.${y}
(( y-- ))
done

Hi Ahmad,

Your code works well, but you do not need the [0-9] and if you change the (( y-- )) and the [[ ]] it will be posix compliant:

Code:
x=10.121.123.114
y=${x##*.}
while [ $y -ge 0 ]
do
  echo ${x%.*}.${y}
  y=$(( y-1 ))
done

# 5  
Old 12-29-2009
Quote:
Originally Posted by Scrutinizer
Hi Ahmad,

Your code works well, but you do not need the [0-9] and if you change the (( y-- )) and the [[ ]] it will be posix compliant:

Code:
x=10.121.123.114
y=${x##*.}
while [ $y -ge 0 ]
do
  echo ${x%.*}.${y}
  y=$(( y-1 ))
done


Np problem man this ([[ & (())) is because I am using bash...but ${x##[0-9]*.} is just an easy way to insure that the input is a number
else it will give an error.
# 6  
Old 12-29-2009
Hi Ahmad, that is the thing. If your last number is e.g. a letter your code will not raise an error, whereas if you leave out the [0-9] it will.
If I feed e.g.:
Code:
x=10.123.4.A

the output will be :
Code:
10.123.A

Whereas if we leave out the [0-9]:
Code:
./test: line 3: [: a: integer expression expected

which is what you want. The pattern operator will not raise the error, but the test will.
Last edited by Scrutinizer; 12-29-2009 at 06:03 AM..
# 7  
Old 12-29-2009
No problem man...SmilieSmilieSmilieSmilieSmilieSmilieSmilieSmilieSmilie
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