Shell Programming and Scripting

Code:

awk '{a[NR]=$0} END {while (NR) print a[NR--]}' mail.log | awk '/Feb  2/ {print ;exit;}'

first, can this code be combined into one?

what i want this code to do is output every single line it finds up until the last occurrence of "Feb 2".

right now, this code simply outputs one line, and aborts. but i want it to output all the lines it finds up until the very last occurrence of "Feb 2".

It looks like your current script is trying to print lines in reverse order. Assuming that what you want to do is print lines from mail.log from line 1 through the last line that contains Feb 2 (and print nothing if that string does not appear in the input file), you could try something like:

Code:

awk '{a[NR]=$0}
/Feb  2/{last=NR}
END {for(i=1;i<=last;i++)print a[i]}' mail.log

Since you didn't supply any sample input or desired output, this is untested. But, if I understood your requirements correctly, it should be close to what you need as long as you have room to read the entire file into memory.

As always, if you're running this on a Solaris/SunOS system, change awk to /usr/xpg4/bin/awk, /usr/xpg6/bin/awk, or nawk.

what i want to do is print the file in reverse order and abort after the very last line containing the string i specified is found.

Reversing the order and talking about the last line matched creates an ambiguity. Making the wild assumption that you want to print the end of the file from the last line in the file that contains the pattern to the end of the file with the output printed in reverse order you should just need to change the last line of the script I suggested to:

Code:

END {if(last)for(i=NR;i>=last;i--)print a[i]}' mail.log

Again, with no sample input and expected output, this is untested.

Combining your (skysmart's) approach with Don Cragun's, try

Code:

awk '{a[NR]=$0} /Feb  2/ {last=NR} END {while (NR >= last) print a[NR--]}' file

The difference between these two approaches is that if Feb 2 is not found in the file, my script will print nothing while RudiC's script will print the entire file in reverse order. From the discussion in this thread, I don't know which outcome is preferred.

both of these commands worked great.

however, just one thing. it appears the awk code aborts immediately after the first entry containing "Feb 2" is found. i want it to abort when the last entry is found.

so, it should keep going up until the "Feb 2" string changes to something else.