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So it should print lines only if followed by the same starting sequence?

Thanks for the reply. Ya you are wright like , it should check the following line is also =035 if so print the second column value, if followed by =245 should skip it.Please guide

Regards
uma

This does what you want (I think...)

Code:

$ perl -0777 -nle 'print "\nBefore:\n$_\n\n"; s/^(.*)/\1\n/sg; s/=035\s+.*?\n=245.*?\n//g; print "Eliminate pattern:\n$_\n\n"; while (/=035\s+(.*)/g) {print "$1\n";}' data4.txt
Before:
=245 this is testing
=035 abc123
=245 this is testing1
=035 abc124
=245 this is testing2
=035 abc125
=035 abc126
=245 this is testing3
=035 abc127
=035 abc128
=035 abc129
=245 this is testing 4

Eliminate pattern:
=245 this is testing
=035 abc125
=035 abc127
=035 abc128


abc125
abc127
abc128

Code:

diff urfile <(uniq -f 2 urfile)
7d6
< =035 abc126
10,11d8
< =035 abc128
< =035 abc129

Hope this will help.

Code:

awk '!/035/ {f=0;s="";}f{ print s} /035/ {f++; s=$NF; } ' file

Example:

Hi,Drewk thanks a lot , it works perfect, can u also help me to understand the codelogic.

Hi Dennis ,thanks when i run your code, its more or less correct but extracting few others which is followed by =245 , this is happening especially in the starting and in the end.

Hi rdcwayx, sorry diff is not working.

Glad it worked. It is not that hard once you get the right regex pattern.

Here is a simpler, easier version to understand:

Code:

$ cat data4.txt
=245 this is testing
=035 abc123
=245 this is testing1
=035 abc124
=245 this is testing2
=035 abc125
=035 abc126
=245 this is testing3
=035 abc127
=035 abc128
=035 abc129
=245 this is testing 4

$ perl -0777 -nle 'while (/=035\s+(.*)\n(?!=245)/g) { print "$1\n"; }' data4.txt
abc125
abc127
abc128

So two things to note:

perl -0777 -nle 'while (/=035\s+(.*)\n(?!=245)/g) { print "$1\n"; }' data4.txt

1) The invocation of perl with -0777 means slurp the whole file. This means the entire file will be in memory since you are referring to multiple lines. You could write something that will read multiple lines, but that is more complex logic. Perl can handle very big files this way, but nonetheless, it may fail with really huge files...

2) Note the Regex of "/=035\s+(.*)\n(?!=245)/g" used in the while loop. Here are the details:

"=035\s+" matches the =035 then any number of non CR whitespace until anything that is not whitespace;
"(.*)" captures the remainder of the line, up to the \n;
"\n" matches the end of line;
"(?!=245)" is a 'zero-width negative lookahead assertion'. In plain English, that means 'don't match the last bit if the next bit is true;'
"g" means all of these patterns.

On the last post, I did it quickly which usually means more sloppy. The last one first printed the input, then deleted the pattern matching a line with =035.* followed by a line with =254.* -- then print the remaining =035 lines. I did it stepwise instead of one sweep...

I cannot overemphasize how easy this becomes if you use a regex tool.

Try this: Regex Powertoy (interactive regular expressions) or this RegExr: Online Regular Expression Testing Tool

Either one, you can just play with patterns on your sample text until it does what you expect. There >>can<< be some bugs, such as gskinner does not handle the negative lookahead or lookbehind assertions properly, but it sure beats scratching your head...

Cheers,