sed: replace a certain pattern with an arbitrary string in between

Question

I'm trying to clean up a log file for better readability - there's a load of un-necessary stuff there to my needs - i basically have to replace sshd[xxxx] where xxxx is an arbitrary number with, well, either a space or nothing. While i can replace a known string, i have no idea how to do a sed wildcard in this case- So- how do i do that?

Answer 1

its not clear whether you want the replace the "sshd" as well, so i assumed you it is.

   sed 's/sshd\[[0-9]*\]//g' file

otherwise,

   sed 's/sshd\[[0-9]*\]/sshd[]/g' file

Answer 2

You are looking to replace all numbers after sshd inside [] with nothing. To select numbers you can use a range [0-9]\+, where [0-9] matches any digit and \+ means one or more of that before.

So for your case the regexp to replace numbers with zeros would be

sed -r s/\[[0-9]\+\]/\[\]/

where the -r enables extended regexp's like the one above. The \[ and \] are just to escape the [ and ] so they don't get interpreted by sed.

For regexp operators like \+ have a look at this section in the gawk manual, for character list like [0-9] see this section -- most of what you see there applies to sed as well.