In order to run a script the file must have an executable permission bit set.
In order to fully understand Linux file permissions you can study the documentation for the
chmod command. chmod, an abbreviation of change mode, is the command that is used to change the permission settings of a file.
To read the chmod documentation for your local system , run
man chmod or
info chmod from the command line. Once read and understood you should be able to understand the output of running ...
ls -l foo.sh
... which will list the READ, WRITE and EXECUTE permissions for the file owner, the group owner and everyone else who is not the file owner or a member of the group to which the file belongs (that last permission group is sometimes referred to as "world" or "other")
Here's a summary of how to troubleshoot the Permission Denied error in your case.
$ ls -l foo.sh # Check file permissions of foo
-rw-r--r-- 1 rkielty users 0 2012-10-21 14:47 foo.sh
^^^ | ^^^ ^^^^^^^ ^^^^^
| | | | |
Owner| World | |
| | Name of
Group | Group
Owner has read and write access rw but the - indicates that the executable permission is missing
chmod command fixes that. (Group and other only have read permission set on the file, they cannot write to it or execute it)
$ chmod +x foo.sh # The owner can set the executable permission on foo.sh
$ ls -l foo.sh # Now we see an x after the rw
-rwxr-xr-x 1 rkielty users 0 2012-10-21 14:47 foo.sh
^ ^ ^
foo.sh is now executable as far as Linux is concerned.
Using sudo results in Command not found
When you run a command using sudo you are effectively running it as the superuser or root.
The reason that the root user is not finding your command is likely that the
PATH environment variable for root does not include the directory where
foo.sh is located. Hence the command is not found.
The PATH environment variable contains a list of directories which are searched for commands. Each user sets their own PATH variable according to their needs.
To see what it is set to run
env | grep ^PATH
Here's some sample output of running the above
env command first as an ordinary user and then as the root user using sudo
rkielty@rkielty-laptop:~$ env | grep ^PATH
rkielty@rkielty-laptop:~$ sudo env | grep ^PATH
[sudo] password for rkielty:
Note that, although similar, in this case the directories contained in the PATH the non-privileged user (rkielty) and the super user are not the same.
The directory where
foo.sh resides is not present in the PATH variable of the root user, hence the command not found error.