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Interested in switch -P what does it do? And "G\t" pattern explanation?

Please do not explain du -xh or basics of command grep.

du -xh / | grep -P "G\t"
5.1G    /var/oracle/XE/datafile
5.1G    /var/oracle/XE
5.1G    /var/oracle
1.1G    /var/lib
6.9G    /var
1.9G    /opt/softwareag/webMethods/install/fix
1.9G    /opt/softwareag/webMethods/install
1.2G    /opt/softwareag/webMethods/Designer
1.3G    /opt/softwareag/webMethods/common
1.9G    /opt/softwareag/webMethods/CCE
1.2G    /opt/softwareag/webMethods/IntegrationServer/instances/default/replicate/salvage
3.0G    /opt/softwareag/webMethods/IntegrationServer/instances/default/replicate
2.3G    /opt/softwareag/webMethods/IntegrationServer/instances/default/packages
5.5G    /opt/softwareag/webMethods/IntegrationServer/instances/default
5.5G    /opt/softwareag/webMethods/IntegrationServer/instances
5.7G    /opt/softwareag/webMethods/IntegrationServer
16G     /opt/softwareag/webMethods
16G     /opt/softwareag
16G     /opt
1.1G    /usr/share
3.0G    /usr
11G     /u01/app/oracle/oradata/XE
11G     /u01/app/oracle/oradata
12G     /u01/app/oracle
12G     /u01/app
12G     /u01
39G     /
2

As explained in the grep manual, -P enables the use of PCREs, i.e. Perl Compatible Regular Expressions.

The PCRE expression G\t matches a G followed by a tab.

The effect is that you only get a listing of directories whose size is listed in gigabytes (or whose name happens to match the pattern).

An alternative pipeline that would more reliable match the G at the end of the first tab-delimited column only:

... | awk -F '\t' '$1 ~ /G$/'
  • 1
    Thank you a lot, i understand now. I saw from man pages , but could not understand until u explained. And i dont know why guys are giving bad points for post, when this is website for helping others. If i m less cleaver then you, and dont understand it alone, its not reason to give minus points for post. No question that is asked is bad. – Miloš Stojanović Jun 18 at 10:22
  • @MilošStojanović Sorry, but I did not downvote your question. That must have been somebody else. People downvote questions for all sorts of reasons, ranging from bad grammar or unreadable text to leaving out information. – Kusalananda Jun 18 at 10:25
  • I m just wondering. Can u help and give me advice how to make new lines when i type the post? because everything is staying at the same line. And only ```` trick i know ```` but that cant be used for simple text,because i got correction already by some people for using it for simple text. – Miloš Stojanović Jun 18 at 10:28
  • @MilošStojanović use <br /> or double new line. – rush Jun 18 at 10:30
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    @Milo you can use the formatting sandbox (meta.stackexchange.com/q/3122/270345) to test formatting and unix.stackexchange.com/editing-help to learn the syntax – muru Jun 18 at 10:36
1

-P enables Perl-compatible regex engine, which isn't the default one. In your example it is required to make \t treated as a tab symbol.

Otherwise grep will consider it as a plain t (escaped with \).


PS. You could easily figure this out based on man page:

OPTIONS
<..>
Matcher Selection
   <..>
   -P, --perl-regexp
          Interpret the pattern as a Perl-compatible regular expression (PCRE).  This is experimental and grep -P may warn of unimplemented features.

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