[ale] Bash scripting q

[JK]

J. D. wrote:
> Is the desired effect for it to expand to /home/callinguser/user? 

No, the desired effect is for it to expand to the home
directory of the user name supplied to the script as
arg $1.  So if I say:

./myscript joe

I need a way within myscript to refer to "joe"'s home, which on
my system happens to be /home/joe.  I cannot make any such
assumptions about the target system, though (that user home
directories live under /home, I mean).  Which is why I
want to use the tilde.

-- JK

> Usually the tilda should expand to /home/user right? I'm not sure why 
> you are using the tilda. $USER is a bash builtin but I guess there is no 
> harm in resetting it.
> 
> for me this works:
> 
> #!/bin/bash
> 
> USER=$1
> cp foo /home/$USER
> chown $USER /home/$USER/foo
> 
> 
> On Thu, May 8, 2008 at 3:38 PM, JK <jknapka at kneuro.net 
> <mailto:jknapka at kneuro.net>> wrote:
> 
>     Hi folks,
> 
>     I am trying to do a very simple thing, and getting screwed by bash's
>     evaluation
>     rules.  Basically, I need to write a script that accepts a user name,
>     and then
>     copies some files to that user's home dir, and also chowns them to that
>     user.
>     So I tried the obvious:
> 
>     #!/bin/bash
>     USER=$1
>     cp foo  ~$USER
>     chown $USER ~$USER/foo
> 
>     This totally fails to work as I expect, because tilde expansion happens
>     before variable expansion.  So if I supply 'joe' as the first arg,
>     "~$USER"
>     expands to ~joe (instead of the desired /home/joe), and the cp
>     effectively
>     evaluates to "cp foo '~joe'", which ends up creating a regular file
>     named
>     ./~joe
> 
>     Is there a clean workaround?  I'd rather not force the user to
>     supply both
>     the user name and the user's home directory as script arguments.  And
>     doing a grep'n'cut on /etc/passwd is not too appealing either.  I've
>     checked
>     a couple of books ("bash Cookbook", "Linux Shell Scripting", and an
>     online tutorial or two), but the most any of them say is "Don't do
>     that";
>     they provide no workaround.
> 
>     An explicit command to force shell expansion of an arbitrary string
>     would
>     do the trick... I'm goofing around with echo and eval right now, with
>     interesting, but not useful, results...
> 
>     Oops, just stumbled on an answer:
> 
>      cp foo $(eval echo $(echo ~$USER))
> 
>     works, although it makes my eyes water a bit.  Is there a better way?
>     (This post has devolved to the "Linux trivia quiz" level...)
> 
>     Thanks,
> 
>     -- Joe
> 
>     --
>     I do not particularly want to go where the money is -
>      it usually does not smell nice there. -- A. Stepanov
> 
> 
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-- 
I do not particularly want to go where the money is -
  it usually does not smell nice there. -- A. Stepanov