Advanced Bash-Scripting Guide:
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2.1. Invoking the script

Having written the script, you can invoke it by sh scriptname, [1] or alternatively bash scriptname. (Not recommended is using sh <scriptname, since this effectively disables reading from stdin within the script.) Much more convenient is to make the script itself directly executable with a chmod.

Either:

chmod 555 scriptname (gives everyone read/execute permission) [2]

or

chmod +rx scriptname (gives everyone read/execute permission)

chmod u+rx scriptname (gives only the script owner read/execute permission)

Having made the script executable, you may now test it by ./scriptname. [3] If it begins with a "sha-bang" line, invoking the script calls the correct command interpreter to run it.

As a final step, after testing and debugging, you would likely want to move it to /usr/local/bin (as root, of course), to make the script available to yourself and all other users as a system-wide executable. The script could then be invoked by simply typing scriptname [ENTER] from the command line.

Notes

[1]	Caution: invoking a Bash script by `sh scriptname` turns off Bash-specific extensions, and the script may therefore fail to execute.
[2]	A script needs read, as well as execute permission for it to run, since the shell needs to be able to read it.
[3]	Why not simply invoke the script with `scriptname`? If the directory you are in ($PWD) is where scriptname is located, why doesn't this work? This fails because, for security reasons, the current directory is not by default included in a user's $PATH. It is therefore necessary to explicitly invoke the script in the current directory with a `./scriptname`.

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