Re: how to manipulate data like awk or perl when visiting a file

[Xah Lee]

On Dec 28, 8:14 pm, rea...@newsguy.com wrote:
> I want to get a leg up on how I might manipulate a file like I can
> with shell tools or awk/perl.
>
> Examples:  I want to display only the first field of lines 30 thru 75
>            I want to reverse field 1 and 5 and print those plus 6 of
>            each line.
>            I want to add up the numbers that appears in field 7 of
>            lines 11 through 28 printing the total to ~/sumtot.txt
>
> I'd like to see a few basic examples and maybe I'll be able to get the
> idea enough to do some of that when I need to.
>
> I don't really want to start way at the beginning of elisp to get
> started.   I hoped maybe there are some examples like that available
> in existing info documents.
>
> I haven't noticed much talk here about those kinds of chores so maybe
> elisp isn't a good choice for that?


do you want to do this as interactive use or do you mean how to do it
in elisp?

For elisp, here's a example:

• How To Process A File Line By Line In Elisp
  http://xahlee.org/emacs/elisp_process_lines.html

for your task, perhaps it's easier to simply read all content in a
file, use split-string so that each line becomes a list item, then use
split-string again on each item so that you got the fields.

Of course, you can also just write your code in awk or perl, and have
a emacs wrapper to call them as emacs commands. See

• Elisp Wrapper For Perl Scripts
  http://xahlee.org/emacs/elisp_perl_wrapper.html

For interactive use, depending what specifically what you want to do,
but it might be easier to simply use shell-command or shell-command-on-
region, and call your sed awk.

  Xah
∑ http://xahlee.org/

☄