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Moderator
Moderator
  • 902 Views

I show you mine, you show me yours: What is your favorite regex to use?

I troubleshoot botched configs very often and I hate seeing the annotations (comment lines), they distract from the main lines in a configuration file, and makes it harder to find the erronous line.

I use this:

 

grep '^[^#]' /path/to/file

or

 

grep -vE ‘^\s*(#|$)’ /path/to/file

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Don't forget to thank those who helped you out with kudos!Both will strip your config file of lines beginning with a # and blank lines, but the latter also strips those lines which have spaces then the #.

 

 

 

 

 

 

 

 

 

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6 Replies
Moderator
Moderator
  • 888 Views

Re: I show you mine, you show me yours: What is your favorite regex to use?

Hey, Ricardo!

I like that negative match in the first regex. I usually do it in a slightly longer way with tr:

$ grep -v '^[[:space:]]*#' /some/file | tr -s '\n'

The reason I commonly go for the tr command at the end is that I may be processing several files at the same time, but in a different way, and then simply just squeeze consecutive newlines (i.e. an empty line is simply two newline characters in a row) in the combined output.

$ (grep -v '^[[:space:]]*#' /some/file ; grep -v '^[[:space:]]*"' /another/file) | tr -s '\n'

And although it isn't really a regular expression, my favourite has got to be producing a list of directories sorted by their disk usage, but using human-friendly suffixes like M/G (which are otherwise unsortable):

$ du -s /some/parent/dir/* | sort -rgk1 | cut -f 2- | tr '\n' '\0' | xargs -0 du -sh

The use of tr here will prevent any problems due to spaces in filenames - I know GNU xargs has an option to specify the delimiter, but unfortunately sometimes I still have to work with other systems which don't come with GNU xargs.

Cheers!

A black cat crossing the street signifies that the animal is going somewhere.
[don't forget to kudo a helpful post or mark it as a solution!]
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kaiser Mission Specialist
Mission Specialist
  • 848 Views

Re: I show you mine, you show me yours: What is your favorite regex to use?

Piping the 'sort' and 'tr' is nice but same output without the 'cut' command

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DavidOBrien Flight Engineer
Flight Engineer
  • 808 Views

Re: I show you mine, you show me yours: What is your favorite regex to use?

I use this all the time to spell-check all my XML files in courseware:

 

find . -iregex .*keyword.*.xml -exec aspell -c '{}' \; 
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Flight Engineer kubeadm Flight Engineer
Flight Engineer
  • 801 Views

Re: I show you mine, you show me yours: What is your favorite regex to use?

Mine is "captain hook"  -    (/.*)?

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Flight Engineer RJ Flight Engineer
Flight Engineer
  • 724 Views

Re: I show you mine, you show me yours: What is your favorite regex to use?

Hey Kubeadm, 

Can you give us an example of that "captain hook"?

 

Thanks!

 

RJ

RJ
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Flight Engineer RJ Flight Engineer
Flight Engineer
  • 728 Views

Re: I show you mine, you show me yours: What is your favorite regex to use?

Nice methods.  I also used:

egrep -v \# /path/to/config | grep . 

That drops all comments, and empty lines as well.  I like the examples presented earlier too.  Strictly speaking, it's not a regex, but it functions well. 

I do however do things like this often in kickstarts for instance:

/bin/mkdir -p /{cdrom,mnt,iso}/notmounted

mydate=`date '+%Y%m%d_%H%M%S'`;echo $mydate

/bin/cp -v /etc/pam.d/system-auth-ac{,.$mydate} 

then run whatever script I plan on knowing I have a backup of the file with a good time date stamp.

 The other day, it was:

tail -f /var/log/{messages,secure,sssd/*log} 

 

RJ
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