Re: [PLUG] pushd and popd on debian squeeze

[JP Vossen <jp@jpsdomain.org>]

> Date: Thu, 25 Aug 2011 14:35:20 -0400
> From: Michael Lazin<microlaser@gmail.com>
> Subject: [PLUG] pushd and popd on debian squeeze
>
> Hi, I am trying to run a bash script on debian squeeze that uses pushd and
> popd.  They are not in the path and when I got to the root directory as root
> and type "find -name pushd" nothing comes up.  Why are these missing from
> debian?  How can I get them?


> Date: Thu, 25 Aug 2011 14:40:45 -0400
> From: Douglas Muth <doug.muth@gmail.com>
>
> They're shell commands.

True in bash.  Note the bash 'help' command, which is *much* more useful 
than the 'man' command for builtins!  See also the 'type -a' command.  I 
thought 'which' was an alias to 'type -a' but at least on Squeeze it 
isn't.  Huh.

[jp@bitbox2:T2:L1:C1:J0:2011-08-25_15:00:21_EDT]
/home/jp$ cat /etc/debian_version
6.0.2

[jp@bitbox2:T2:L1:C2:J0:2011-08-25_15:00:25_EDT]
/home/jp$ help pushd
pushd: pushd [-n] [+N | -N | dir]
    Add directories to stack.
[...]

[jp@bitbox2:T2:L1:C4:J0:2011-08-25_15:01:05_EDT]
/home/jp$ type -a pushd
pushd is a shell builtin


> Make sure your script starts with:
>
> #!/bin/bash
> and NOT:
> #!/bin/sh

It's slightly more secure to use (note trailing -):
	#!/bin/bash -
	or
	#!/bin/sh -

I *think* I talked about that in 
http://princessleia.com/plug/2009-Secure_Shell_Scripts.pdf.


> While sh is usually symlinked to bash, if it's run as sh, it will
> emulate the Bourne Shell, and bash-specific commands like pushd and
> popd will not be available.

True on Debian, but watch out!  That has *not* been true on Ubuntu for a 
while now, and it *will* get you in to trouble if you assume '/bin/sh' 
is really sorta-kinda bash.  For details see 
http://princessleia.com/plug/2008-JP_bash_vs_dash.pdf.

Short version: /bin/sh --> dash (*not* bash) on Ubuntu, and dash != 
bash!  Heck, sh != bash != dash, while we're at it.  "Portable" shell 
scripts can be really hard to write, that's partly why Perl exists. :-) 
 (And no, I don't wanna hear about zsh Paul... ;-)

HTH,
JP
----------------------------|:::======|-------------------------------
JP Vossen, CISSP            |:::======|      http://bashcookbook.com/
My Account, My Opinions     |=========|      http://www.jpsdomain.org/
----------------------------|=========|-------------------------------
"Microsoft Tax" = the additional hardware & yearly fees for the add-on
software required to protect Windows from its own poorly designed and
implemented self, while the overhead incidentally flattens Moore's Law.
___________________________________________________________________________
Philadelphia Linux Users Group         --        http://www.phillylinux.org
Announcements - http://lists.phillylinux.org/mailman/listinfo/plug-announce
General Discussion  --   http://lists.phillylinux.org/mailman/listinfo/plug