copying songs (first real program)

amy

Interested in commenting a simple (but useful) new program?

I realized that it's very tiring collecting manually all music from your hard disk and copying it to (for instance) an mp3 player. So, since I use rhythmox with playlists I thought it would be nice if you could just make quot;cpquot; use all songs listed in an exported playlist and copy them to a given directory. So, since I have never programmed anything quot;realquot; outside algorithm competitions, I decided to make this program on my own for practice: quot;m3ucpquot;.  It uses .m3u playlists (m3u is the simplest playlist format IMO, maybe I'll add other formats later) to quot;cpquot; songs to given directories. Source is attached to this post (I needed to add .txt to upload), it's a small program.

Anyway, I would like to hear comments about the program. Anything: idea, code readability, performance, features that could be added (just don't complicate too much ), what I must do... The only bug I know for now is strings' bound checking.

Remember, I'm a n00b in practical coding and I'm still learning, so just post all your critics, good or bad.
BTW, this is the first time I used C, not C++ (thought I should practice it too).

Hi there,

A C app might be a little overkill for this particular task ... you may be making life more complicated than it needs to be. For instance, if you knew an m3u only contained absolute references to local files, the same task could be performed with a single shell command...
Code:
for i in $(sed  '/^\s*$\|^#.*/d' test.m3u); do cp $i /dest/path; done
In reality of course, there are lots of reasons why something that simple would break, so a short shell script would be required (to properly handle ucls, relative paths, and files with odd characters in the filenames). Personally, I would be tempted to go that route, for simplicity's sake.


Originally Posted by kiddersA C app might be a little overkill for this particular task

The problem is that I only know BASIC, Pascal and C++. I never tried to learn shell scripting (now I see even more that I should). Maybe I should have used C++ (for simplicity's sake ) because it makes strings easier. But I wanted this to be a practice of coding too. I think I'll rewrite it to C++ soon.Originally Posted by kiddersto properly handle ucls

I never thought of ucls, thanks.Originally Posted by kiddersfiles with odd characters in the filenames

That's why I use quotation marks for directories from m3us and use '\' for quotation marks that are part of the directory only. I think this should work. Does it? Are quotation marks only one to worry about if filename is written inside quotation marks?
This is confusing to explain. For instance, I use:
Code:
quot;/home/user/some new directory/a file with \quot;quotes\quot;quot;instead of:
Code:
/home/user/some\ new\ directory/a\ file\ with\ \quot;quotes\quot;
Thanks for reply.

Oh, I noticed a bug in line 52: there's something missing at the beginning of the line:
Code:
if( i gt; 0 )
Relative path handling was done in a hurry. Without this quot;ifquot; the program will not work when it is executed in the same directory as a playlist .

Hey again,Originally Posted by MiCovranAre quotation marks only one to worry about if filename is written inside quotation marks?

I wonder how characters like '$', '[', 'gt;', 'amp;', and so on would be treated. The results could be quite dangerous if your quot;cpquot; command arguments aren't properly escaped.

I would suggest learning Python first.  Just my opinion.  You want to start with something that will allow you to do everything you want instead of several languages, bash does this, C/C++ does that, etc.  Sometime down the road you can decide if you want to learn other languages as well.

I wonder how characters like '$', '[', 'gt;', 'amp;', and so on would be treated.

I just can't seem to find any info about these '\' and 'quot;' symbols for linux command line on the internet. I'm not brilliant in internet browsing, so if anyone knows where I can find something about this topic, could you post it, please?

The results could be quite dangerous if your quot;cpquot; command arguments aren't properly escaped.

What do you mean?

Hey again,

Dwblas's suggestion is a good one!  Having said that, I get the impression that C's difficulty level, or suitability (or unsuitability!) for the task at hand aren't particularly important to you ... ie you just want to take C on a test drive for a while. I'm all in favour of that.

With any language though, the problems start when you have to start interfacing the the environment you're running in. The answer to both of your questions, I suppose, is quotroper escaping is pretty criticalquot;. Consider these, as simple (albeit unrealistic) examples:

I - Linux shell
For some reason, you write a script (or for that matter, any program that executes an quot;mvquot; command) to move files to a user-specified location. You ask the user for $DEST, and do...
Code:
mv (.. long list of files here ..) $DEST
Now, imagine $DEST is quot;dev/null; rm -Rf ~quot;. If the semicolon isn't handled correctly, the result could be...The list of files are moved into oblivion ... ie essentially deleted.
The entire home directory of the user running the command is erased.
Naturally, no matter how silly (or malicious) a user is when he specifies his target location, there should simply be no way to persuade a program to have this effect.

II - SQL
Imagine you'd written a login script for a website that uses the following SQL to match a user-provided username amp; password to an existing account...
Code:
SELECT * FROM account WHERE username='lt;usernamegt;' AND password='lt;passwordgt;' LIMIT 1
By specifying a username of quot;  ' OR TRUE OR '  quot;, a user could manipulate the query into returning results it shouldn't, possibly leading to a successful login.

Again, there should of course be no way for a user to manipulate a website into this kind of behaviour.
In more realistic terms, the point is that certain characters/symbols invariably have special meanings in a given context. For instance, you can't often call variables things like quot;forquot;, quot;ifquot; or quot;casequot;, in many programming languages. If you fail to handle quot;specialquot; symbols properly, even completely innocent use of any program can lead to disaster.

One common technique, used to replace special characters with substitutes that don't have any special meaning, is called quot;escapingquot; (that word should help with web searches). As a simple illustration:Code:
touch 1;rm 1
Question: Does the user mean quot;Touch a file called '1' and then delete itquot;, or quot;Touch a file called '1;rm 1'quot;? The above does the former; the below does the latter.Code:
touch 1\;rm\ 1
I hope that helps.

I would suggest learnign python ruby or perl for this. THis is just one of those things though that perl is made for, but seriously I would suggest python or ruby, maybe perl later on when it upgrades to perl 6.

(sorry perl was my first language so i have a slight fondness for it and ruby)


Originally Posted by Note360I would suggest learnign python ruby or perl for this. THis is just one of those things though that perl is made for, but seriously I would suggest python or ruby, maybe perl later on when it upgrades to perl 6.

(sorry perl was my first language so i have a slight fondness for it and ruby)

While that may be the case, wouldn't that defeat the whole purpose of him wanting to practice with C?

I am sure there are 100s of ways to do this program, each way would be 'best' in some aspect, ie: - a one line shell script- a 200 byte executable stripped-assembly program- a native, standalone and distributable C program- a python program a n00b can whip up in 2 minutes- a robust multi-platform Java application

I think this would be a useful little program to brush up on your C skills


Originally Posted by AlexThomson_NZWhile that may be the case, wouldn't that defeat the whole purpose of him wanting to practice with C?

I am sure there are 100s of ways to do this program, each way would be 'best' in some aspect, ie: - a one line shell script- a 200 byte executable stripped-assembly program- a native, standalone and distributable C program- a python program a n00b can whip up in 2 minutes- a robust multi-platform Java application

I think this would be a useful little program to brush up on your C skillsYou are right in all respects. All languages could or should be able to do this task (idk if Javascript can). Any way, I like that you did it in C I like C better than C++ even though I am a object oriented man, mainly for syntax reasons (which is why I like C# with Mono). Good luck with this. Actually this would be a fun programming challenge for all of us (what happened to that series of threads)