Shell Programming and Scripting

Thanks for the information.

I perform the vast majority of my programming on OS X, so running the commandman 1 findwill not provide the text that you quoted from the find man page you'll find on a Linux system.

For the record, on OS X (and I imagine on BSD and most UNIX-branded systems) that command line writes diagnostic messages similar to:

Code:

find: illegal option -- n
find: illegal option -- a
find: illegal option -- m
find: illegal option -- e
find: *.WAV: No such file or directory

to standard error and exits with exit code 1.

Hello,

I tried ls -lf on a subdirectory of the main directory Music,. and got a huge list of files in 3 columns

Code:

ajayram@pc13:/media/HITACHI/Music/Hindi Music$ ls -lf
...
Abhijeet Sawant/                                                 Piya Haji Ali-Nusrat Fateh Ali Khan.WAV                    Rang De Basanti/
Agnee/                                                           AlbumArt_{95109B16-8980-425B-9D75-7C1BD9569130}_Small.jpg  Rangeela/
Aisha/                                                           AlbumArt_{ADAE49DB-6396-4F0A-86E3-79DF94F56DAF}_Large.jpg  Refugee/
I hate love stories/                                             AlbumArt_{ADAE49DB-6396-4F0A-86E3-79DF94F56DAF}_Small.jpg  Rock on/
Instant Karma/                                                   AlbumArt_{D4826E15-A4F0-4E8C-8448-2C5DB13E3C86}_Large.jpg  Saajan/
Jaan Leva.WAV                                                    AlbumArt_{D4826E15-A4F0-4E8C-8448-2C5DB13E3C86}_Small.jpg  Saawariya/
...

The output is in unsorted order.

I then scanned the output for .WAV files ie reading Column 1 from top to bottom, then Column 2 and then Column 3 and it gives the same output as this find command run on the top level directory ..

Code:

ajayram@pc13:/media/HITACHI/Music$ find -name *.WAV

So does the find command work like this ? It takes the input directory and goes through all sub directories and executes

Code:

 ls -lf

and filters from that the files of the required type ( here in this case *.WAV)

However, I have another doubt, when I ran the find command on the top level Music Directory, the Music Directory had no *.WAV files in it , but only in the directories beneath it, thus it gave the desired output,. I expected a similar output when I go to the Hindi Music Directory, I thought that find would give me all the *.WAV files in that directory and directories beneath it.

But it just returns one line of the output and throws up and error !

Code:

ajayram@pc13:/media/HITACHI/Music/Hindi Music$ find -name *.WAV 
find: paths must precede expression: Baazigar Title Track.WAV
Usage: find [-H] [-L] [-P] [-Olevel] [-D help|tree|search|stat|rates|opt|exec] [path...] [expression]

could someone please clarify this ?

Yes. This is exactly what Jim Mcnamara and I have been describing in our posts on this thread.
NO! The find utility does not call the ls utility to read directories. The find utility and the ls utility both read directories on their own. (If you want to know what is going on under the covers, look at the opendir() and readdir() functions manual pages on your system.)

The find utility does not sort directory entries after reading them; the ls utility sorts directory entries unless the -f option is in effect.
This is a completely different topic based on the need to use appropriate quoting mechanisms when expanding filenames in the shell (especially when those filenames may contain <space> or <tab> characters like the names of your .WAV files do). When you ask the shell to run the command:

Code:

find -name *.WAV

the shell sees an unquoted *.WAV pathname pattern and expands it to a (sorted) list of files in the current directory that match that pattern. Then it calls find with each element of that list as a separate argument.

The find -name primary expects to see a single filename pattern as an argument, but instead you are giving it a list of files. The find utility looked at its arguments, determined that the first filename in the list was to be used as the -name primary's pattern argument, and saw more arguments that didn't match the name of any of find's primaries or operators. Therefore, it gave you a diagnostic message for the second filename expanded from the *.WAV pattern by the shell and quit.

If you use the shell's quoting rules to avoid the shell's pathname pattern matching expansions, you will get what you want. In this case, any of the following:

Code:

find -name '*.WAV'
find -name "*.WAV"
find -name \*.WAV

and well over a hundred other ways of quoting this string will work as you expected.

Note that the behavior of the command you gave without quoting *.WAV will vary depending on how many files match the pattern in the directory where you run the command. If there aren't any files matching that pattern in the directory where you ran the command (such as your top level music directory, you'll get what you wanted because the pattern expands to itself when there are no matches. Had there been exactly one file that matched, find would find the file you wanted in the current directory, but would have found *.WAV files in subdirectories only if they had the same name as the file matched in the current directory.