Shell Programming and Scripting

Hello All,

I am not well-versed with Unix commands. While practicing I got following situation.

My current working directory is empty and firstly, I created a file “test*” then I can see the file got created:

Code:

> ls -ltr
total 0
>
> touch test*
>
> ls -ltr
total 0
-rw-rw-rw-    1 kimxk    users             0 Sep 28 12:41 test*

Then I removed “test*” file and created two new files named “test1*” and “ test2*”:

Code:

> rm *
>
> touch test1* test2*
> ls -ltr
total 0
-rw-rw-rw-    1 kimxk    users             0 Sep 28 12:42 test2*
-rw-rw-rw-    1 kimxk    users             0 Sep 28 12:42 test1*

But again when I tried to create “test*” file this file is not created:

Code:

> touch test*
> ls -ltr
total 0
-rw-rw-rw-    1 kimxk    users             0 Sep 28 12:42 test2*
-rw-rw-rw-    1 kimxk    users             0 Sep 28 12:42 test1*
>

Query: Why it is not creating “test*” file if “test1*” and “ test2*” files already exists?

Many thanks in advance.

Regards,
Manish

This probably has to do with you use of *. The file name test* refers to any file that starts with test and has anything after it, like.

test1
test2
test.txt
test.whatever
...

you should probably not use the * to create a single file. It really doesn't make any sense since its purpose is to refer to anything that starts with whatever is before the *, or anything that has a specific ending.

You can use * to do things like "delete all files with the extension .txt"

rm *.txt

or copy everything that starts with 44 to a new directory

cp 44* ./newdir/

and things like that.

LMHmedchem

You need to know that whenever you type in anything on the command line, your shell interprets the command line first and then the corresponding commands are called.
It is dangerous to include * in file-names.

Echo is nice debug command. Easy to see how shell expand the line before execute it.

Code:

echo touch test*

Thank you all for the explanations.
I understand that it is dangerous to include * in file-names but only trying to understand some basic working knowledge (behind the scene)

I got to know somewhere that:
rm *\* --> is the script that removes all files that end with an asterisk in the name.
rm *\** --> is the script that removes all files that contain an asterisk in the name.

example:

> touch test test1* test2* make*a*chance create*all
>
> ls -l
total 0
-rw-rw-rw- 1 kimxk users 0 Oct 01 11:32 create*all
-rw-rw-rw- 1 kimxk users 0 Oct 01 11:32 make*a*chance
-rw-rw-rw- 1 kimxk users 0 Oct 01 11:32 test
-rw-rw-rw- 1 kimxk users 0 Oct 01 11:32 test1*
-rw-rw-rw- 1 kimxk users 0 Oct 01 11:32 test2*
>
===================== rm *\* =================================

> rm *\*
>
> ls -l
total 0
-rw-rw-rw- 1 kimxk users 0 Oct 01 11:32 create*all
-rw-rw-rw- 1 kimxk users 0 Oct 01 11:32 make*a*chance
-rw-rw-rw- 1 kimxk users 0 Oct 01 11:32 test
>
=====================================================


==================== rm *\** ============================

> rm *\**
>
> ls -l
total 0
-rw-rw-rw- 1 kimxk users 0 Oct 01 11:37 test
>
======================================================


I understand that in both the commands 1st '*' is meant to read and remove all the files current directory but not able to understand how the 2nd & 3rd '*' impacting this.


Many thanks in advance.

Regards,
Manish

I like more to talk about file generation.
* in the filename is only char *.
*\* or *'*' start with 0-n chars (not begin .) and last char is *
=> * , 1*1*1*, **, ***, ****, all match.
Sameway dos a'like *.* result is
=> a.b.c.d match : start with 0-n some chars, then is dot and after that is 0-n chars.
* include all chars including *.

Use echo to test

Code:

echo .?*
echo *\**
echo *.*

Why echo is good ?
Because command line is parsed by shell, including file name generation and the result has given for command. So echo print out all arguments = what shell has done for the command line before give it to the command.

Thanks a lot for the explanation.