non-recursive alias

[phidebian]

Yall,

I got something I don't understand, must be me mis-reading the docco, yet after multiple read I still don't get it.

This is about non recursive alias, yet it looks like some recursion prevention is applied.

$ cat s.sh
#!/bin/false

echo this is s.sh
type echo
alias e='echo'
type e
e this is the e alias

$ ksh -c "source ./s.sh;e post-source e"
this is s.sh
echo is a shell builtin
e is an alias for echo
ksh: source: ./s.sh[7]: e: not found
ksh: e: not found

Apparently the 2 'e' invocation are not found even though there is no recursion here.
When doing thins in an interactive shell (instead of -c) I got

$ ksh

TC$ source ./s.sh                                                   
this is s.sh
echo is an alias for print
e is an alias for echo
ksh: source: ./s.sh[7]: e: not found

TC$ e post-source
post-source

again the 'e' inside the sourced file is not found, but the post-source is ok in interactive mode.

Why this difference.

Note that bash behave the same, so I am sure I am wrong somewhere but don't know where.

Thanx in advance for any pointers.

[phidebian]

FWIW zsh behave differently

$ cat s.sh
#!/bin/false

echo this is s.sh
type echo
alias e='echo'
type e
e this is the e alias

$ zsh -c "source ./s.sh;e post-source e"
this is s.sh
echo is a shell builtin
e is an alias for echo
this is the e alias
zsh:1: command not found: e

The difference here is this is the e alias which is 'not found' for ksh93 and bash

[McDutchie]

The answer to the riddle is that the . and source commands in ksh93 read and parse the entire dot script before executing it, in a single sh_eval call here:

ksh/src/cmd/ksh93/bltins/misc.c

Line 330 in 0818a7d

sh_eval(iop,sh_isstate(SH_PROFILE)?SH_FUNEVAL:0);

Since everything is parsed before any alias command is executed, such aliases are not expanded unless defined outside the dot script first. This behaviour is currently unique to ksh93, but POSIX explicitly allows it.

As for bash, it has alias expansion disabled for scripts by default; you have to run it in POSIX mode or explicitly shopt -s expand_aliases to enable it. After that it will act like other non-ksh93 shells.

[phidebian]

Jeez I lost sight of this one, I'd better rely on $ expansion then

$ cat sd.sh
#!/bin/false

echo this is sd.sh
e='echo'
$e this is the \$e expansion

$ ksh -c 'source ./sd.sh;echo e=$e;$e post-source e'
this is sd.sh
this is the $e expansion
e=echo
post-source e

@McDutchie for your explanations.

[McDutchie]

Or you could set a shell function like e() { echo "$@"; }. Functions can be redefined just like aliases or variables.