Bash development

jhwilliams · 06-22-2007, 10:05 PM

I often inadvertantly forget to actually write chmod when issuing ugo-w type options.

That is, I write (incorrectly, but would like to do so validly)

Code:

u-w filename

when i mean

Code:

chmod u-w filename

and the like.

I got to wondering... can't I just have bash natively understand these sorts of file permissions requests? I could write out aliases in a ~/.aliases file for every possible [ugo][-+][rwx] request, but that would take a long time, and there's probably a better way to do it... any ideas? Thanks!

wjevans_7d1@yahoo.co · 06-23-2007, 12:41 AM

Three points.

First, ~/.aliases is not a file that bash normally reads. If you wish to adopt that convention, be sure to source that file from ~/.bashrc and either ~/bash_profile or ~/.profile.

Second, there are more possibilities than [ugo][+-][rwx], as the man page will show. But maybe those are all the possibilities you use. Which is perfectly fine.

Third, if those are all the possibilities you use, it would not take a long time to write out all of those aliases. There are only 18 of them. Copy and paste 'em from here if you like:

Code:

alias u+r='chmod u+r'
alias u+w='chmod u+w'
alias u+x='chmod u+x'
alias u-r='chmod u-r'
alias u-w='chmod u-w'
alias u-x='chmod u-x'
alias g+r='chmod g+r'
alias g+w='chmod g+w'
alias g+x='chmod g+x'
alias g-r='chmod g-r'
alias g-w='chmod g-w'
alias g-x='chmod g-x'
alias o+r='chmod o+r'
alias o+w='chmod o+w'
alias o+x='chmod o+x'
alias o-r='chmod o-r'
alias o-w='chmod o-w'
alias o-x='chmod o-x'

In case you're curious, I didn't type them all by hand. I whipped up this shell script to do it for me:

Code:

#!/bin/sh

for xxx in u g o
do
  for yyy in + -
  do
    for zzz in r w x
    do
      echo alias $xxx$yyy$zzz=\'chmod $xxx$yyy$zzz\'
    done
  done
done

Hope this helps.

jhwilliams · 06-23-2007, 12:47 AM

[ugo]*[+-][rwx]* is what I should have typed. There would then be 6*2*6 = 72 possible ways or writing it. I like the script idea, though. I'll give that a try. As for the .aliases... I adopted this file so that multiple shells could read from one place and the file would have a neutral name. Thanks for the help

archtoad6 · 06-25-2007, 02:53 PM

Actually,I think this is what you want/meant:

Code:

{{u{g{o,},o,},g{o,},o}}{+,-}{{r{w{x,},x,},w{x,},x}}

This gives, not the 72 possibilities you mentioned, but the 98 possibilities you implied (7*2*7, because 2^3-1=7). With the asterisks, technically "uuuu+xxxx" would satisfy the pattern. While your code would not produce "ugo+rwx".

The script might then look like this:

Code:

for X in {{u{g{o,},o,},g{o,},o}}{+,-}{{r{w{x,},x,},w{x,},x}}
do
   echo alias $X=\'chmod $X\'
done

A possibly less messy alternative:

Code:

for X in \
`echo -e {{u,}{g,}{o,}}{+,-}{{r,}{w,}{x,}}"\n" \
  | egrep '[ugo]+[+-][rwx]+'`
do
   echo alias $X=\'chmod $X\'
done

pixellany · 06-25-2007, 05:13 PM

"Swimming upstream against the tide"---how's that for a redundant metaphor??

You are talking about changing some paradigms that have survived in the Unix world since the 70s. Not how I choose to spend my time.......YMMV.

archtoad6 · 06-25-2007, 05:28 PM

No one asked us if this set of aliases is a good idea.

I'm sure that someone out there can tell us why it's a very bad one.

It just seemed like an interesting exercise in logic & coding.

wjevans_7d1@yahoo.co · 06-26-2007, 08:21 AM

No no no. It's a very good idea, if that's what increases the original poster's productivity.

Quoth pixellany:

Quote:

You are talking about changing some paradigms that have survived in the Unix world since the 70s.

Not at all. He's adding new commands which are shortcuts. He types his commands faster than otherwise, and gets more work done.

What paradigms are being changed?

archtoad6 · 06-26-2007, 08:44 AM

I await pixellany's response w/ bated breath. (And that's not sarcasm; hyperbole, maybe, but not sarcasm.)

Meanwhile, I have a gut feeling that cluttering the command structure this way may be bad. In any case, why not just alias chmod itself to something shorter like "cm"?

pixellany · 06-26-2007, 08:52 AM

Quote:

Originally Posted by archtoad6

I await pixellany's response w/ bated breath. (And that's not sarcasm; hyperbole, maybe, but not sarcasm.)

Meanwhile, I have a gut feeling that cluttering the command structure this way may be bad. In any case, why not just alias chmod itself to something shorter like "cm"?

Was that "bated" or "baited"----whole different meaning.....

I was reacting to the initial post which said--in part:

Quote:

can't I just have bash natively understand these sorts of file permissions requests?

---and went on to say something about aliases being too much trouble.

I could type "chmod" several hundred times in the time that it has taken to respond to this thread. This said, I must confess that--as an engineer--I very often go to great lengths to develop labor-saving shortcuts--ones whose typical payback time is measured in years..

jhwilliams · 06-26-2007, 12:13 PM

Yea, I was 5 when Trovalds started Linux; I'd have to say that my allegiance to UNIX paradigms is minimal. It seems to me that file permissions are overlooked by the novice or are a nuissance to set in the daily affairs of more advanced users, and since there isn't any other reasonable interpretation of the options, it would do everyone a favor.

It makes sense too:
rw+ugo filename
"Do the rw operation on filename from here on..."

Probably you're right though, it wouldn't end up saving alot of time. I was in this mostly as a thought experiment.