Why does a #!/bin/bash script handle aliasing worse than a #!/bin/sh script?

**UmberGryphon** · 06-09-2006

A stripped-down example script that demonstrates the behavior that's befuddling me:

Code:

#!/bin/sh
alias foo=bar
foo

returns "bar: command not found", which is what I expect that script to return. On the other hand,

Code:

#!/bin/bash
alias foo=bar
foo

returns "foo: command not found", as if the alias command was ignored.

If anything, I'd expect the /bin/sh version of the script to ignore the alias, for possible compatibility with old scripts written for a version of /bin/sh that wasn't just a link to bash.

Could someone explain this behavior to me, please? It happens on more than one Linux distro, and even on Cygwin's bash under Windows (where /bin/sh is a copy of /bin/bash, not a symbolic link to it).

UmberGryphon
(who will just start his script with #!/bin/sh in the meantime)

**drl** · 06-10-2006

Hi.

Aliases are not expanded when the shell is not interactive, unless the
expand_aliases shell option is set using shopt (see the description of
shopt under SHELL BUILTIN COMMANDS below ...
-- man bash

So for

Code:

#!/bin/bash

# @(#) s2       Demonstrate alias.

shopt -s expand_aliases
alias foo=bar
foo

We would see:

Code:

$ ./s2
./s2: line 7: bar: command not found

cheers, drl

**vlsimpson** · 06-10-2006

You really shouldn't use aliases in scripts anyway. Write functions instead.

Just my opinion though.

**drl** · 06-10-2006

Hi, vlsimpson.

Always glad to see another viewpoint -- is there any specific reason behind your opinion -- performance, maintenance, etc? ... cheers, drl

**vlsimpson** · 06-10-2006

Originally Posted by drl

Hi, vlsimpson.

Always glad to see another viewpoint -- is there any specific reason behind your opinion -- performance, maintenance, etc? ... cheers, drl

Just more versatile mainly.

**ajayh** · 07-12-2006

I do found the same problem.

Is there any Version Compatibility

Either upgrade the version of bash or run configure under another shell
(such as /bin/sh).

Other suggestion of using function is good, as maual says

"For almost every purpose, shell functions are preferred over aliases. "

**drl** · 07-12-2006

Hi, ajayh.

What specific advantages have you found to favor the use functions over aliases? ... cheers, drl

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