[buug] ~, shell script programming, etc. (wee bits from last BUUG meeting, plus a bit more

[Michael Paoli]

from an sh(1) man page:
    Tilde Expansion (substituting a user's home directory)
      A word beginning with an unquoted tilde character (~) is subjected to
      tilde expansion.  All the characters up to a slash (/) or the end of the
      word are treated as a username and are replaced with the user's home
      directory.  If the username is missing (as in ~/foobar), the tilde is
      replaced with the value of the HOME variable (the current user's home
      directory).

$ echo ~
/home/m/michael
$ echo \~
~
$ echo '~'
~
$ echo "~"
~
$

But not all shells are created equal - notice the differing behaviors
between bash and dash, for the versions at my fingertips, in the case
where HOME isn't set:
$ bash -c 'unset HOME; echo ~'
/home/m/michael
$ dash -c 'unset HOME; echo ~'
~
$

Somewhat hazardous:
#!/bin/sh
cd ~/some_directory
./some_program

A bit better:
#!/bin/sh
cd ~/some_directory &&
./some_program

Typically even better for a shell script:
#!/bin/sh
set -e
cd ~/some_directory
./some_program

With -e set, upon error (non-zero return for shell command) the shell
exits non-zero, rather continuing execution.  This is typically what one
wants.

references:
2009-05-07 BUUG meeting
sh(1)
http://www.rawbw.com/~mp/unix/sh/#Good_Programming_Practices