UNIX for Dummies Questions & Answers

I have a file with hundreds of lines in it. I wanted to extract anything that matches the following:

KR followed by 4 digits:
example KR1201

Code:

cat list | sed "s/[KR[0-9$]//g"

Is the closest I've come, and obviously it is not what I want. This would remove all of the items that I want and leave me with the rest of the text. I've tried sed -n and /p' but this doesn't work and I'm confused about the syntax. I know other ways to do this with egrep and grep -w but I want to learn to do it in sed.

The one thing I don't want to do is print the rest of the line; I want only to print the KR1201 or KR followed by 4 digits. There is something missing in my syntax; not sure how to encapsulate the pattern.

As with sort, sed takes pathname operands. Using:

Code:

cat file | sed [options] [OtherOperands]

instead of:

Code:

sed [options] [OtherOperands] file

wastes system resources, slows down your system for other users who may be sharing your system, and makes your command line run slower.

If you have an input file named list containing:

Code:

nothing from this line
KR1201
abcKR3012
KR1111def
defKR3333extra
12345KR678910

Previous line was empty; neither of these should appear in output

and you run the command:

Code:

sed -n 's/\(.*\)\(KR[0-9][0-9][0-9][0-9]\).*/\2/p' list

using a standards conforming version of sed, you get the output:

Code:

KR1201
KR3012
KR1111
KR3333
KR6789

The Linux sed man page says:
and in the description of the sed s(ubstitute) command says: But, there is no other mention of sub-expressions on that man page.

Note that this sed command makes no effort to find more than one occurrence of your pattern if it appears more than once on a single line

I've learned a lot from your sed/sort tutorials and today was able to solve a sort problem on my own for once after reading all your posts. I thank you for taking the time out of your day to really create detailed posts with examples! This is much more helpful than any textbook!