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Re: system-command-exists-p


From: Andreas Röhler
Subject: Re: system-command-exists-p
Date: Mon, 07 Dec 2009 13:02:34 +0100
User-agent: Thunderbird 2.0.0.19 (X11/20081227)

Pascal J. Bourguignon wrote:
> Andreas Roehler <address@hidden> writes:
> 
>> Hi,
>>
>> needed a check if a command exists on system.
>> Employed the following:
>>
>> (defun system-command-exists-p (command)
>>   "Return t if COMMAND is available on system. "
>>   (let* ((cmd (format "type %s" command)))
>>     (eq 0 (shell-command cmd))))
>>
>> Any comments/suggestions?
> 
> Use %S or (shell-quote-argument command).
> 
> type is a built-in command specific to the sh familly of shells.
> Perhaps it would be a good idea to explicitely call up sh?


> 
> It may be useful to return the path of the command:
> 
> (defun system-command-exists-p (command)
>   "Return t if COMMAND is available on system. "
>   (let* ((cmd (format "/bin/sh -c 'type %s'" 
>                       (shell-quote-argument command))))
>     (when (eql 0  (shell-command cmd))
>       (let ((result (shell-command-to-string cmd)))
>         (if (string-match "^.* is \\(.*\\)\n$"result)
>             (match-string 1 result)
>             result)))))
> 
> (mapcar (function system-command-exists-p)
>         '("cat" "type" "foo"))
> --> ("/bin/cat" "a shell builtin" nil)
> 
> 
> 

Thanks a lot.

Concerning the  precise kind-of-"shell"-question, I'm not sure.
Case is to write a check for pack-unpack functions.

Presently dired-do-compress uses a hard-encoded "gzip", replaced here by
a choice so far.

Then testing all compressing/uncompressing possibilities, it turns out some 
might not be installed.

type uncompress =>
uncompress is /usr/bin/uncompress
type compress =>
bash: type: compress: not found

Test should not fail, if these programms are not installed, rather give a 
message.
So far the issue here.

Think the shell-in-use should not matter, resp. will be selected already.

What about to write:

(cmd (format (concat (getenv "SHELL") " -c 'type %s'")

Thanks again

Andreas




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