Date: Tue, 09 Feb 1999 04:43:47 +1000 From: Greg Black <gjb@comkey.com.au> To: root@isis.dynip.com Cc: ben@scientia.demon.co.uk, freebsd-questions@FreeBSD.ORG Subject: Re: Help About Shell Script Message-ID: <19990208184347.13321.qmail@alpha.comkey.com.au> In-Reply-To: <199902080041.DAA21348@isis.dynip.com> of Mon, 08 Feb 1999 03:41:47 %2B0300 References: <199902080041.DAA21348@isis.dynip.com>
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Warning: this is fairly long, but it does include a proper
illustration of a solution further down.
> >> What if we wanted to tke the variables i and j
> >> from a file.
> >
> > That would depend what format the file was. At the simplest level, with
> > two files called "current_i" and "current_j", containing the numbers
> > alone, you can read that like so:
> >
> > i=$(cat current_i)
> > j=$(cat current_j)
> That's too simple, but kinda reduntant, they are actually 4 loops
> inside one-another, can't think of creating 4 files each containing an
> integer, this won't be programming, its carpenting.
Indeed.
> > If the file contains something like
> >
> > i=5
> > j=18
> >
> > you could probably do
> >
> > eval $(cat name_of_the_file)
>
> did not get this one, you mean ;
>
> i= $(cat name_of_the_file) ???
No, he meant what he wrote. Think about it.
> if that's what you mean, then you solved my problem.
I don't think so, because it's absurd.
> > I'd recommend using Perl if you go much more complex.
>
> Ya, That's aa coooool thing to learn, I have seen what perl scripts can
> do. But I think its very extensible language, I mean I'll be 65 years
> before I reach the bottom of it, is that so, I'm ready to learn new
> things, and always wish to learn the devls such as perl, tcl, tk, but
> I'm kinda afraid that they'd be difficult for me to learn.
This is sad. Perl is worth avoiding (for reasons that I'm happy
to elaborate on, but won't do here).
For complex multi-user GUI-based applications that need to be
developed quickly, you can't go past a combination of Python for
the scripting stuff, Tk for the GUI stuff (via Python's tkinter
module) and (if it involves data) PostgreSQL for a database engine.
But, to return to the question (which has got very muddy now),
there's no reason at all to use anything more complex than a
standard shell script for the kind of stuff that has been
discussed in this thread.
Here's an example -- it's a little bit contrived since it was
whipped up for this illustration, but it's real enough to make
some kind of sense.
Say we have a data file with records stored one per line with
names and addresses like this:
----------
Smith,James Alan Will,25 Wilson St,West Gosford,NSW,2456,02-9876-5432
Jones,Mary-Anne,23/567 Harrison Ave,Indooroopilly,Qld,4068,07-3456-7890
Anderson-Smythe,Jim,106 Veronica St,Camberwell,Vic,3126,03-9988-7766
----------
Simple enough: 7 fields per record -- Surname, First Name(s),
Street, Suburb, State, Postcode, Phone No -- each field
separated by a comma and the records in any order. Now, say we
want to print the data neatly formatted, sorted by surname, then
we can use this trivial shell script:
----------
#!/bin/sh
sort -t , addr.dat | (
IFS=",
"
while read surname firstname street suburb state pcode telno ; do
printf "%8s: %s %s\n" Name $firstname $surname
printf "%8s: %s\n" Address $street
printf "%8s %s %s %s\n" "" $suburb $state $pcode
printf "%8s: %s\n\n" Phone $telno
done
)
----------
Save the data in a file called addr.dat and run the script and
you'll get:
Name: Jim Anderson-Smythe
Address: 106 Veronica St
Camberwell Vic 3126
Phone: 03-9988-7766
Name: Mary-Anne Jones
Address: 23/567 Harrison Ave
Indooroopilly Qld 4068
Phone: 07-3456-7890
Name: James Alan Will Smith
Address: 25 Wilson St
West Gosford NSW 2456
Phone: 02-9876-5432
If you wanted them sorted by postcode rather than surname, you
would change the sort command to key on the 6th field like this:
sort -t , -k 6 addr.dat
None of this is rocket science and none of it needs anything
more complex than the standard shell and standard unix commands
that have been around for years.
So go and play with this and see how it works, and empower
yourself with the wonderful programming environment that you get
for free in FreeBSD.
--
Greg Black <gjb@acm.org>
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