Shell Programming and Scripting

Hi All,

I have a file in which i have to search for a pattern from the beginning of the file and if the pattern is found , then i have to perform a reverse search from that line to the beginning of the file to get the first occurrence of another pattern.

sample input file

Code:

hey
what are you doing
IM324
A1
iam doing mca
how about you?
IM326
B2

as like mentioned above, the files contains a lots of patterns like this.
for example i have the patttern "B2" as first pattern and if that is found , i have to get first occurence of "IM..." which is associated with it. This IM pattern may be immediately above B2 or a few lines above too

if you people have some idea, Please share with me

Code:

awk '$0 ~ /^IM/ {f=$0;next} $0 ~ /^B2/ {if(f){f=f"\n"$0;print f;f="";next}} {if(f) f=f"\n"$0;}' inputFile

Code:

sed -n '/IM/h;/B2/{g;p;}' infile

@Scrutinizer, I guess

Code:

sed -n '/IM/h;/B2/{H;g;p;}' infile

To print line having last pattern too.

That is correct, although I did not gather that this is required..

OR may be like this:

Code:

sed -n 'H;/IM/h;/B2/{g;p;}' infile

as above one will not print lines between patterns (as shown below). The only thing with this is that, there has to be starting pattern, otherwise (if starting pattern is not found) everything upto Ending pattern will be printed

Code:

hey
what are you doing
IM324
A1
iam doing mca
how about you?
IM326
dfgdgfdg
dfgdfgfdg
B2

Hi Anurag,

Could you please explain how it works?