Bash - "/" is a directory

Question

This is really confusing...

I currently have a Debian 8 computer, and I connect to it using PuTTY (SSH).
The default console used is Bash.

When I try to pass a path to an alias, it gives the following error:

 -bash: /: Is a directory

Here is an example:

Also, there's a bizarre behaviour: running '/' or "/" cause the same error, as if Bash were ignoring quotes.

If it matters, the alias explorer was defined like this:

alias explorer='pcmanfm 1>/dev/null 2>&1 &'

Is this the expected behaviour?
If not, what am I doing wrong?

_Also, there's a bizarre behaviour: running '/' or "/" cause the same error, as if Bash were ignoring quotes._ - What are you expecting bash to do when you type `'/'`? — marcelm, Jun 24 '16 at 22:00
@marcelm A syntax error, a warning or just displaying `/` (similar to `echo`). — Ismael Miguel, Jun 24 '16 at 22:11
The syntax is fine so there is no syntax error, you **do** get a warning ("/: Is a directory"), and just displaying `/` would be inconsistent with anything else bash does. Try comparing the results of entering `'garply'`, `'ls'`, `'/bin/ls'`, `'/bin'` and `'/'`? Also try them without the quotes; why would the quotes change the result? — marcelm, Jun 24 '16 at 23:01
You might find this [explanation of **how quotes relate to argument lists**](http://stackoverflow.com/a/13819996/5419599) helpful. Particularly the last paragraph. — Wildcard, Jun 24 '16 at 23:27

score 14 · Accepted Answer · edited Jun 24 '16 at 17:42

14

The way you wrote your alias, the command you run would be expanded as

pcmanfm 1>/dev/null 2>&1 & '/'

This will run pcmanfm without any options as a background job and then try to run / as a command.

You probably want a function instead of an alias

explorer() { pcmanfm "$@" >/dev/null 2>&1 & }

edited Jun 24 '16 at 17:42

terdon

answered Jun 24 '16 at 16:59

Stephen Harris

But `'/'` is in single quotes. Why would Bash even attempt to run it? (I understand if it was with `"/"`) – Ismael Miguel Jun 24 '16 at 17:00
2

`'/foo/bar/baz'` will try and run the command; the quotes here don't matter. – Stephen Harris Jun 24 '16 at 17:02
10

@IsmaelMiguel the quotes are irrelevant. The point is that the `&` is a [list terminator](http://unix.stackexchange.com/a/159514/22222) so bash reads the next item (whatever that may be) as a command. – terdon Jun 24 '16 at 17:41
@terdon So, if I do `echo 'a' & 'rm -rf /'`, it will nuke my system? – Ismael Miguel Jun 24 '16 at 19:37
Thank you a lot for the function. I really tried a function before, but, I couldn't do it. I am accepting this answer since it is the first one and provides a fix. – Ismael Miguel Jun 24 '16 at 19:38
4

@IsmaelMiguel no, `'rm -rf /'` tries to run a command containing 8 characters. It's highly unlikely there is such a command so it will fail. On the other hand `'rm' '-rf' '/'` will succeed in running the `rm` command with an instruction to (attempt to) remove the entire filesystem. – roaima Jun 24 '16 at 19:43
@roaima That almost makes sense to me. But, that is an entirelly new question. Thank you a lot for explaining it to me. – Ismael Miguel Jun 24 '16 at 19:48

score 4 · Answer 2 · answered Jun 24 '16 at 17:00

4

The alias provides a literal expansion. So running explorer / maps to

pcmanfm 1>/dev/null 2>&1 & /

This runs pcmanfm in the background, immediately followed by / in the foreground.

answered Jun 24 '16 at 17:00

roaima

That addresses the `explorer /`, but not the quoted `/`. But it is still correct. – Ismael Miguel Jun 24 '16 at 19:39
1

@IsmaelMiguel `'/'` is identical to `/`. What is there to explain? – roaima Jun 24 '16 at 19:41
That they are identical? – Ismael Miguel Jun 24 '16 at 19:44
@IsmaelMiguel why do you expect them to be different? – Random832 Jun 24 '16 at 19:55
Is `'rm'` the same as `rm` or `"rm"`? – Ismael Miguel Jun 24 '16 at 21:51
@IsmaelMiguel yes. The quotes don't make any difference here. Not when the word inside them is being treated as a command and the quotes don't protect a word from being treated as a command. – terdon Jun 24 '16 at 22:18
@terdon That begs the question: "What would protect a word from being treated as a command, besides comments?" – Ismael Miguel Jun 24 '16 at 22:22
1

@IsmaelMiguel nothing, really, it depends on how it is presented to the shell. That does deserve it's own question though. – terdon Jun 24 '16 at 22:22

2 Answers2