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Re: Editing a piped in stream?

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On 07/06/18 09:17, Richard Owlett wrote:
> Subject line is poorly phrased.
> While working on a problem {solved by a different approach} I had:
>     ls -l /dev/disk/by-label/ | cut -f 10,12 -d ' ' data.txt
> I would then manually edit data.txt by replacing the space character 
> between the two fields with a tab.

I assume you meant:

     ls -l /dev/disk/by-label/ | cut -f 10,12 -d ' ' > data.txt


(It is best to cut and paste from a console session, rather than typing 
untested commands and/or output into a post.)


> I suspect I should be able to do:
>     ls -l /dev/disk/by-label/ | cut -f 10,12 -d ' ' | *something* > 
> prettydata.txt
> 
> I searched for examples/tutorials found that it should be conceptually 
> possible. However the examples I found were processing streams I didn't 
> understand.
> 
> What should I be looking for?

Beware that ls(1) with the -l option can produce output with a variable 
number of spaces between fields:

2018-07-06 18:51:53 dpchrist@po ~
$ ls -l /bin/e*
-rwxr-xr-x 1 root root 31464 Feb 22  2017 /bin/echo
-rwxr-xr-x 1 root root    28 Jan 23  2017 /bin/egrep


When you feed that to cut(1) and change the delimiter to a space, the 
result is broken (and impossible to fix?) because cut(1) expects exactly 
one delimiter between each field:

2018-07-06 18:52:27 dpchrist@po ~
$ ls -l /bin/e* | cut -f 6,7,9 -d ' '
Feb 22 2017
   Jan


What you want is a tool that can handle fields delimited by one or more 
whitespace characters.  Regular expressions come to mind, but RTFM 
cut(1) doesn't look promising:

2018-07-06 18:53:45 dpchrist@po ~
$ ls -l /bin/e* | cut -f 6,7,9 -d '\s+'
cut: the delimiter must be a single character
Try 'cut --help' for more information.


Perhaps awk(1) or sed(1) (?).


Perl with the -a (autosplit) and -e (evaluate) options is ideal in this 
situation, replacing both cut(1) and "something":

2018-07-06 18:55:29 dpchrist@po ~
$ ls -l /bin/e* | perl -ae 'print join("\t", @F[5,6,7]), "\n"'
Feb	22	2017
Jan	23	2017


Perhaps other people will post solutions in their favorite scripting/ 
programming language.  These give you more power and control than 
traditional shell pipelines and command-line tools.  You should consider 
learning one.


David

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Thread

Editing a piped in stream? Richard Owlett <rowlett@cloud85.net> - 2018-07-06 18:20 +0200
  Re: Editing a piped in stream? Michael Wagner <wagner_m_bremen@web.de> - 2018-07-06 18:50 +0200
    Re: Editing a piped in stream? Richard Owlett <rowlett@cloud85.net> - 2018-07-06 20:30 +0200
  Re: Editing a piped in stream? john doe <johndoe65534@mail.com> - 2018-07-06 19:10 +0200
  Re: Editing a piped in stream? David Christensen <dpchrist@holgerdanske.com> - 2018-07-07 04:10 +0200
    Re: Editing a piped in stream? John Crawley <john@bunsenlabs.org> - 2018-07-07 11:00 +0200
      Re: Editing a piped in stream? David Christensen <dpchrist@holgerdanske.com> - 2018-07-07 21:40 +0200
        Re: Editing a piped in stream? David Wright <deblis@lionunicorn.co.uk> - 2018-07-08 03:40 +0200
          Eureka;/ Re: Editing a piped in stream? Richard Owlett <rowlett@cloud85.net> - 2018-07-08 13:00 +0200
        Re: Editing a piped in stream? John Crawley <john@bunsenlabs.org> - 2018-07-08 03:40 +0200
          Re: Editing a piped in stream? john doe <johndoe65534@mail.com> - 2018-07-08 07:40 +0200
            Re: Editing a piped in stream? Andy Smith <andy@strugglers.net> - 2018-07-08 13:20 +0200
              Re: Editing a piped in stream? Richard Owlett <rowlett@cloud85.net> - 2018-07-08 15:20 +0200
                Re: Editing a piped in stream? Richard Owlett <rowlett@cloud85.net> - 2018-07-08 16:00 +0200
                Re: Editing a piped in stream? John Darrah <xyllyx@gmail.com> - 2018-07-08 18:50 +0200
                Re: Editing a piped in stream? mick crane <mick.crane@gmail.com> - 2018-07-10 14:20 +0200
                Re: Editing a piped in stream? Greg Wooledge <wooledg@eeg.ccf.org> - 2018-07-10 14:40 +0200
                Re: Editing a piped in stream? mick crane <mick.crane@gmail.com> - 2018-07-10 15:00 +0200
                Re: Editing a piped in stream? john doe <johndoe65534@mail.com> - 2018-07-10 15:30 +0200
              Re: Editing a piped in stream? mick crane <mick.crane@gmail.com> - 2018-07-10 14:50 +0200
            Re: Editing a piped in stream? Greg Wooledge <wooledg@eeg.ccf.org> - 2018-07-09 14:50 +0200
              Re: Nvidia drivers Matthew Crews <mattcrews@mattcrews.com> - 2018-07-09 15:20 +0200
                Re: Nvidia drivers Matthew Crews <mattcrews@mattcrews.com> - 2018-07-09 20:40 +0200
                Re: Nvidia drivers Boyan Penkov <boyan.penkov@gmail.com> - 2018-07-09 20:50 +0200

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