awk loop to delete lines ina file

[pb0y]

Hi

I need assistance with a loop routine that counts the number of lines in a file then extracts the last line into a new file. The problem I am running into is the number of lines in file A will be dynamic.

I need a way to subtract the lines in File A one at a time and output them into File B. File B can never have more than one line since I am using the line as a variable for another function. I would prefer to just delete each line from file A and output them to file B but cut is not able to do this and I haven't had much luck with sed.


for i in $fileA
do
x=`cat $i | wc -l`
y=`expr $x - 1`
z=`expr $x - $y`
nawk 'NR == 1, NR == '"$z"' {print}' $i > $FileB

 

[aigles]

Hi,

I think that you can do all work without AWK.

If you want to extract last part of a file use TAIL :
tail -1 file # Extract last line of file
tail -5 file # Extract last 5 lines of file
tail +10 file # Extract last part of file begining at line 10.

If you want to extract first part of a file use HEAD :
head -5 file # Extract first 5 lines of file

And if you want to extract moddle part of a file :
head -5 file | tail +10 # Extract lines from line 5 to line 10 of file. Jean Pierre.

 

[grega]

To process fileA one line at a time in reverse order, you can do

for i in $(tail -r fileA)
do
do your stuff here
done

Greg.

 

[pb0y]

thanks

i got it to work like this

while [ $X != 1 ]

do
X=`expr $X - 1`
head -$X $FileA |tail +$X > $FileB
done