The literal answer is as others have given: because the current directory isn't in your $PATH.

But why? In short, it's for security. If you're looking in someone else's home directory (or /tmp), and type just gcc or ls, you want to know you're running the real one, not a malicious version your prankster friend has written which erases all your files. Another example would be test or [, which might override those commands in shell scripts, if your shell doesn't have those as built-ins.

Having . as the last entry in your path is a bit safer, but there are other attacks which make use of that. An easy one is to exploit common typos, like sl or ls-l. Or, find a common command that happens to be not installed on this system — vim, for example, since sysadmins are of above-average likelyhood to type that.

Does this sound too theoretical? It largely is, but it definitely can happen in reality, especially on multi-user systems. In fact, here is an example from this site where an administrator switched to a users' home directory and found ps to be masked by an executable of that name.

try:

abc/info.exe

but if it's really a Windows program, you will need to install "wine", then do:

wine abc/info.exe

but only some Windows programs will work under wine.

you should give more details. you extract the files from the archive, then what to do next totally depends on the files that were in the archive. so extract the files, and give more details.

Your script should look like:

#!/bin/bash

passwd

Save it in a file, let say password.sh or simple password, then make it executable using next commands in terminal:

cd /path/to/password.sh  #or cd /path/to/password
chmod +x password.sh     #or chmod +x password

To run it from terminal, just use the following command:

./password.sh            #or ./password

or

/path/to/password.sh     #or /path/to/password

To run it only using:

password.sh              #or password

you must to add the path of the script to the PATH. See How to add a directory to the PATH? in this sense.

Give execute permission to your script:

chmod +x /path/to/yourscript.sh

And to run your script:

/path/to/yourscript.sh

Since . refers to the current directory: if yourscript.sh is in the current directory, you can simplify this to:

./yourscript.sh