How to make vertical bar | work in grep

grep

Here's an example of a grep command line I've tried:

grep '(565172|565173|565175)' /var/log/cups/error_log

It doesn't produce any output, even though all 3 values are in the file multiple times.

I tried escaping the bars, and that improved things somewhat – the middle value was detected but not the first or last.

grep '(565172\|565173\|565175)' /var/log/cups/error_log

I also tried double escapes and went back to getting no results.

grep '(565172\\|565173\\|565175)' /var/log/cups/error_log

What am I doing wrong? Thanks.

Best Answer

The syntax you are trying to use belongs to extended regular expressions, so the answer is very simple, either use egrep or include the -E flag.

Related Solutions

How to make grep ignore lines without trailing newline character

grep is explicitly defined to ignore newlines, so you can't really use that. sed knows internally if the current line (fragment) ends in a newline or not, but I can't see how it could be coerced to reveal that information. awk separates records by newlines (RS), but doesn't really care if there was one, the default action of print is to print a newline (ORS) at the end in any case.

So the usual tools don't seem too helpful here.

However, sed does know when it's working on the last line, so if you don't mind losing the last intact line in cases where a partial one isn't seen, you could just have sed delete what it thinks is the last one. E.g.

sed -n -e '$d' -e '/pattern/p'  < somefile                   # or
< somefile sed '$d' | grep ...

If that's not an option, then there's always Perl. This should print only the lines that match /pattern/, and have a newline at the end:

perl -ne 'print if /pattern/ && /\n$/'

Best Answer

Related Solutions

How to make grep ignore lines without trailing newline character

Related Question