[OT] bash help

[Mike Wright]

Hi all,

My brain cell ran away from home.  I have an incredibly simple script 
that doesn't do what I expect.  I use "mkdir DIR; cd DIR" a lot so I'm 
trying to put it in a script: "~/bin/mdcd".

After checking that $1 exists:

dir="$1"
mkdir -p "$dir"
cd "$dir"   <------ never executes

The directory is created so there is no error there.

Huh? Insight anyone?

Thanks,
Mike Wright

[Joe Zeff]

On 02/19/2017 05:22 AM, Mike Wright wrote:
>  Hi all,
>
>  My brain cell ran away from home.  I have an incredibly simple script
>  that doesn't do what I expect.  I use "mkdir DIR; cd DIR" a lot so I'm
>  trying to put it in a script: "~/bin/mdcd".
>
>  After checking that $1 exists:
>
>  dir="$1"
>  mkdir -p "$dir"
>  cd "$dir"   <------ never executes
>
>  The directory is created so there is no error there.
>
>  Huh? Insight anyone? 
I'm not sure why this doesn't work but you're doing it the hard way.

mkdir -p $1
cd $1

is much simpler, and might work better.

[Dave Mitchell]

On Sun, Feb 19, 2017 at 02:12:35PM -0800, Joe Zeff wrote:
>  On 02/19/2017 05:22 AM, Mike Wright wrote:
>  > dir="$1"
>  > mkdir -p "$dir"
>  > cd "$dir"   <------ never executes 

>  I'm not sure why this doesn't work but you're doing it
> the hard way.
>  
>  mkdir -p $1
>  cd $1
>  
>  is much simpler, and might work better. 
Unless $1 contains any spaces, in which case the mkdir will create two or
more directories; e.g.:

    $ p="a b"
    $ mkdir $p
    $ ls -l
    total 8
    drwxrwxr-x. 2 davem davem 4096 Feb 20 09:07 a
    drwxrwxr-x. 2 davem davem 4096 Feb 20 09:07 b
    $


-- 
"You may not work around any technical limitations in the software"
    -- Windows Vista license

[Robert Nichols]

On 02/19/2017 07:22 AM, Mike Wright wrote:
>  Hi all,
>
>  My brain cell ran away from home.  I have an incredibly simple script that doesn't do
> what I expect.  I use "mkdir DIR; cd DIR" a lot so I'm trying to put it in a
> script: "~/bin/mdcd".
>
>  After checking that $1 exists:
>
>  dir="$1"
>  mkdir -p "$dir"
>  cd "$dir"   <------ never executes 
The script runs in a child process. It changes its _own_ working directory and then exits,
leaving the parent shell exactly where it was before. Scripts like that need to be
_sourced_, not simply executed. It probably makes sense to set up an alias to do that:

     alias mkdirp=". mkdirp.sh"

Then you can type "mkdirp /wherever/whatever" and it will run ". mkdirp.sh
/wherever/whatever".

-- 
Bob Nichols     "NOSPAM" is really part of my email address.
                 Do NOT delete it.

[Patrick O'Callaghan]

On Sun, 2017-02-19 at 05:22 -0800, Mike Wright wrote:
>  Hi all,
>  
>  My brain cell ran away from home.  I have an incredibly simple script 
>  that doesn't do what I expect.  I use "mkdir DIR; cd DIR" a lot so I'm
>
>  trying to put it in a script: "~/bin/mdcd".
>  
>  After checking that $1 exists:
>  
>  dir="$1"
>  mkdir -p "$dir"
>  cd "$dir"   <------ never executes
>  
>  The directory is created so there is no error there.
>  
>  Huh? Insight anyone? 
If it's a Shell script then it's executing in a sub-shell, which then
terminates, so the current directory of the calling Shell is unchanged.

To get the effect you want either use an alias or call "eval".

poc

[Mike Wright]

On 02/19/2017 03:46 PM, Patrick O'Callaghan wrote:
>  On Sun, 2017-02-19 at 05:22 -0800, Mike Wright wrote:
> > Hi all,
> >
> > My brain cell ran away from home.  I have an incredibly simple script
> > that doesn't do what I expect.  I use "mkdir DIR; cd DIR" a lot so
> I'm
> > trying to put it in a script: "~/bin/mdcd".
> >
> > After checking that $1 exists:
> >
> > dir="$1"
> > mkdir -p "$dir"
> > cd "$dir"   <------ never executes
> >
> > The directory is created so there is no error there.
> >
> > Huh? Insight anyone?
>
>  If it's a Shell script then it's executing in a sub-shell, which then
>  terminates, so the current directory of the calling Shell is unchanged.
>
>  To get the effect you want either use an alias or call "eval". 
To both Robert Nichols & Patrick O'Callaghan,

Got it - after resolving a "gotcha".  I'm executing this on a machine I 
shelled into.  But after executing the alias mkcd=". 
/home/mike/bin/mdcd" the path is created but I'm bounced all the back to 
my local machine!!!

Turns out the script ended with "exit 0" which apparently is executed in 
the context of the calling bash and logs me out.

Thanks for the help

[T_POL]

On Sun, 19 Feb 2017 05:22:44 -0800
Mike Wright <nobody(a)nospam.hostisimo.com&gt; wrote:

>  Hi all,
>  
>  My brain cell ran away from home.  I have an incredibly simple script 
>  that doesn't do what I expect.  I use "mkdir DIR; cd DIR" a lot so I'm
>
>  trying to put it in a script: "~/bin/mdcd".
>  
>  After checking that $1 exists:
>  
>  dir="$1"
>  mkdir -p "$dir"
>  cd "$dir"   <------ never executes
>  
>  The directory is created so there is no error there.
>  
>  Huh? Insight anyone?
>  
>  Thanks,
>  Mike Wright
>  _______________________________________________
>  users mailing list -- users(a)lists.fedoraproject.org
>  To unsubscribe send an email to users-leave(a)lists.fedoraproject.org 

Hi

not sure about that but I think the "cd" command executes indeed 
but it's valid only for the scripts' environment and not for the 
shell you started the script from.

If it's not so, may be my brain cells are gone too.

Ciao

[Andy Blanchard]

On 20 February 2017 at 09:18, T_POL <t_pol(a)tiscali.it&gt; wrote:
>  not sure about that but I think the "cd" command executes indeed
>  but it's valid only for the scripts' environment and not for the
>  shell you started the script from. 
*ding* *ding* *ding*  We have a winner!

Shells execute in their own instance of bash (or whatever) - a
subshell.  The way to do this is with an alias or function, depending
on your needs (aliases don't except parameters, functions do), so
here's the function for "mdcd":

$ mdcd() {
    # additional checks here, per original post
    mkdir $1
    cd $1
}


Alternatively, you can force a script to run in the current shell by sourcing it

$ . {scriptname}

Note the "." between the prompt and script (you can also use the more
literal "source"):

$ source {scriptname}

Another option, just for completeness, would be to alias sourcing a
script, e.g.:

$ alias mdcd='. {path to script}'

-- 
Andy

The only person to have all his work done by Friday was Robinson Crusoe

[Jon LaBadie]

On Mon, Feb 20, 2017 at 10:46:23AM +0000, Andy Blanchard wrote:
>  On 20 February 2017 at 09:18, T_POL <t_pol(a)tiscali.it&gt; wrote:
>  >
>  > not sure about that but I think the "cd" command executes indeed
>  > but it's valid only for the scripts' environment and not for the
>  > shell you started the script from.
>  
>  *ding* *ding* *ding*  We have a winner!
>  
>  Shells execute in their own instance of bash (or whatever) - a
>  subshell.  The way to do this is with an alias or function, depending
>  on your needs (aliases don't except parameters, functions do), so
>  here's the function for "mdcd":
>  
>  $ mdcd() {
>      # additional checks here, per original post
>      mkdir $1
>      cd $1
>  }
>  
>  
>  Alternatively, you can force a script to run in the current shell by sourcing it
>  
>  $ . {scriptname}
>  
>  Note the "." between the prompt and script (you can also use the more
>  literal "source"):
>  
>  $ source {scriptname}
>  
>  Another option, just for completeness, would be to alias sourcing a
>  script, e.g.:
>  
>  $ alias mdcd='. {path to script}'
>   
A caveat I think the OP already found out.  Both the sourced
script and the function would be running in the users
interactive shell environment, it must for the cd to be effective.
Thus you do not want to "exit" from either the sourced
script nor from the function as that causes the interactive
shell to exit.  In the function you can use "return <status>"
instead of "exit <status>".

Jon
-- 
Jon H. LaBadie                  jonfu(a)jgcomp.com

bash help

[Cameron Simpson]

On 19Feb2017 05:22, Mike Wright <nobody(a)nospam.hostisimo.com&gt; wrote:
> My brain cell ran away from home.  I have an incredibly simple script
> that 
> doesn't do what I expect.  I use "mkdir DIR; cd DIR" a lot so I'm trying
> to 
> put it in a script: "~/bin/mdcd".
>
> After checking that $1 exists:
>
> dir="$1"
> mkdir -p "$dir"
> cd "$dir"   <------ never executes
>
> The directory is created so there is no error there.
>
> Huh? Insight anyone? 
Run you script with -x:

  sh -x your-script.sh args...

My suspicion is that your script work.

_However_, "cd" is a shell builtin because it affects the _current_ process. If

you cd inside a shell script it moves the process running the shell script, 
_not_ your parent shell that invoked the script.

If you want a shell convenience to make a directory an cd into it you need a 
shell function: effectively a piece of script that runs in you current shell 
instead of as a subprocess.

For example, I have a 'cdf" function defined like this:

  cdf(){
    [ $# = 1 ] || { echo "Usage: cdf dir" >&2; return 2; }
    needdir "$1" && cd "$1" && pwd && {
prepdir; L; }
  }

For context, "needdir" is a personal script that effectively does what your 
"mkdir -p" does, except that it checks first and tells me if it needed to make 
the directory; "prepdir" is a personal shell function that is intended to do 
some personal setup (but presently does nothing:-); "L" is a personal shell 
alias for "ls -la".

One important thing to note when writing shell functions: you can leave a shell 
function early (and set its "exit status") with "return". This is like
"exit", 
but it terminates the shell function, not your shell!

Cheers,
Cameron Simpson <cs(a)zip.com.au&gt;