Alias and functions

Aliases are expanded when a function definition is read, not when the function is executed …

$ echo "The quick brown fox jumps over the lazy dog." > myfile
 
$ alias myalias=cat
 
$ myfunc() {
>     myalias myfile
> }
 
$ myfunc
The quick brown fox jumps over the lazy dog.
 
$ alias myalias="ls -l"
 
$ myalias myfile
-rw-r--r-- 1 myusername mygroup 45 Dec 13 07:07 myfile
 
$ myfunc
The quick brown fox jumps over the lazy dog.

Even though myfunc was defined to call myalias, and I’ve redefined myalias, myfunc still executes the original definition of myalias.  Because the alias was expanded when the function was defined.  In fact, the shell no longer remembers that myfunc calls myalias; it knows only that myfunc calls cat:

$ type myfunc
myfunc is a function
myfunc ()
{
cat myfile
}

… aliases defined in a function are not available until after that function is executed.

$ echo "The quick brown fox jumps over the lazy dog." > myfile
 
$ myfunc() {
>     alias myalias=cat
> }
 
$ myalias myfile
-bash: myalias: command not found
 
$ myfunc
 
$ myalias myfile
The quick brown fox jumps over the lazy dog.

The myalias alias isn’t available until the myfunc function has been executed.  (I believe it would be rather odd if defining the function that defines the alias was enough to cause the alias to be defined.)