Question

The question is in the title. I could not find anything on google, so im hoping someone here can explain this to me.

I am using debian 6.0.5 and the shell assigned to the executing user in the /etc/passwd file is /bin/bash

So, simply writing cd ~ works and brings me to the users home directory.

test -d "~/some_dir" returns false in an if statement ( some_dir exsits )

Edit:
Sorry I should’ve been more clear as of why I was writing /bin/bash cd ~ instead of cd ~: I am writing a bash script with #!/bin/bash and the above mentioned if statement ends up in the false clause.

Answer 1

The options for any command line are expanded before the command is run, even for internal commands. Whatever shell you’re using to run /bin/bash cd ~ is presumably interpreting the tilde literally rather than a special character that expands to your home directory.

As a test, try creating a directory by that name and see if the error goes away.

> mkdir ./~
> /bin/bash cd ~

Note that the cd command needs to be done within your running shell to be useful. When you change the working directory of a sub-shell, and then the sub-shell exits, you’ll find yourself back where you started.

UPDATE:

From within a bash script, you should be able to use the $HOME environment variable, which should consistently contain your home directory. I’m not aware what conditions would cause tilde expansion to fail, but I’ve always used $HOME.

Also, when determining whether you can change into a particular directory, you have the option of being explicit and returning useful status:

unset err
if [[ ! -d "$somedir" ]]; then
  err="Can't find $somedir"
elif [[ ! -r "$somedir" ]]; then
  err="Can't read $somedir"
fi

if [[ -n "$err" ]]; then
  echo "$ERROR: $err" >&2
  exit 1
fi

cd "$somedir"

Or, you can just try the CD and look at its results.

if ! cd "$somedir"; then
  echo "ERROR: $somedir not availble"
  exit 1
fi

Detailed error reports are handy, but if you don’t need them, keeping your code small has advantages as well.