Problem with grep matching to end of line
 

Ok, I've been running linux for years and I feel like an idiot even asking this, It's probably going to be a duh answer,but anyways.

I diffed 2 files and grepped the output for just the new stuff and here was the output

I only want the filename part of the output so I made the command

diff ls-lt ls-lt.old | grep '<' | grep -o sn.0[0-3][0-9][0-9].txt

but nothing came out so I played with it for a little while and when i ran this

diff ls-lt ls-lt.old | grep '<' | grep -o sn.0[0-3][0-9][0-9].txt

i got the "sn.0???.tx" output, but i can't get that last "t" out of it? what am I doing wrong, I can just add it to the end of every line, that's not a problem, but I'm wondering what's going on here and how to deal with it in case i have something a little less constant in the future.

Looks like it should work - maybe try quotes on that as well.

Quotes did it. Don't know why I didn't try that... guess i can put my dunce hat on for the night

diff ls-lt ls-lt.old | grep '<' | grep -o 'sn.0[0-3][0-9][0-9].txt'


Thank you, I was about to pull my hair out. I am still curious as to why that is needed. Is there something special about the end of the line or could it be a bug?

You could use "cut" or "awk" to cut out the column you want.

diff ls-lt ls-lt.old | grep '<' | cut -d' ' -f5

diff ls-lt ls-lt.old | awk '/</{ print $5 }'

ok, i'll keep that in mind. I'm writing some scripts that are going to be dealing with more complex filenames and such. I was just curious if there was something that grep was seeing that I don't know about and may become an issue later with other programs like sed and others that use regular expressions

Must be a problem at your machine - I cut some of your data, and the first regex (no quotes) worked fine.

grep start at line
 

How do I start grep at line, say, 200?

(My output is too large and produces a segmentation fault, so i'm going to have to grep each 100 or so lines at a time.)

Maybe wrap it in a loop thus:

which will process it rec by rec, slower, but file size should not be an issue.

Mmmmm - don't know about that; lots of blanks in there to trip over the default IFS.
It were me doing this, at about this point I'd be starting to think perl ....

did you have the same problem with this awk version?

it seems this could be exactly what you want. quick and simple way to do it.

You can set IFS to newline only easy enough.
Perl would be faster though if the file to process is that big, just seemed a bit excessive if he just wants the last field of each rec.
Also depends if this is just a one-off requirement or if its going to be run multiple times.

If you want to use a range of lines, in sed you can start a sed command with a range like,
2000,2500 or use a regular expression like /\[General\]/,/$^/.
You can also use brackets to try to find a match within a range.
Also, using sed, you can add a quit command if you have found a match. That is commonly done to avoid reading all of the lines in a large file.
Using grep, look for the option to return a single result. That will abort after finding a match, and won't continue reading till the end of the file looking for another match.

The cut command would be ideal for cutting out a certain field. That is exactly what the command was written for. You could use head to select the top N lines and pipe the output to cut.

If you want to use a certain range of lines, you can use sed to filter through only those lines and pipe the output to the cut command: