When running scripts in bash, I have to write ./ in the beginning:
$ ./manage.py syncdb
If I don't, I get an error message:
$ manage.py syncdb
-bash: manage.py: command not found
What is the reason for this? I thought . is an alias for current folder, and therefore these two calls should be equivalent.
I also don't understand why I don't need ./ when running applications, such as:
user:/home/user$ cd /usr/bin
user:/usr/bin$ git
(which runs without ./)
Because on Unix, usually, the current directory is not in $PATH.
When you type a command the shell looks up a list of directories, as specified by the PATH variable. The current directory is not in that list.
The reason for not having the current directory on that list is security.
Let's say you're root and go into another user's directory and type sl instead of ls. If the current directory is in PATH, the shell will try to execute the sl program in that directory (since there is no other sl program). That sl program might be malicious.
It works with ./ because POSIX specifies that a command name that contain a / will be used as a filename directly, suppressing a search in $PATH. You could have used full path for the exact same effect, but ./ is shorter and easier to write.
EDIT
That sl part was just an example. The directories in PATH are searched sequentially and when a match is made that program is executed. So, depending on how PATH looks, typing a normal command may or may not be enough to run the program in the current directory.
When bash interprets the command line, it looks for commands in locations described in the environment variable $PATH. To see it type:
echo $PATH
You will have some paths separated by colons. As you will see the current path . is usually not in $PATH. So Bash cannot find your command if it is in the current directory. You can change it by having:
PATH=$PATH:.
This line adds the current directory in $PATH so you can do:
manage.py syncdb
It is not recommended as it has security issue, plus you can have weird behaviours, as . varies upon the directory you are in :)
Avoid:
PATH=.:$PATH
As you can “mask” some standard command and open the door to security breach :)
Just my two cents.
Your script, when in your home directory will not be found when the shell looks at the $PATH environment variable to find your script.
The ./ says 'look in the current directory for my script rather than looking at all the directories specified in $PATH'.
When you include the '.' you are essentially giving the "full path" to the executable bash script, so your shell does not need to check your PATH variable. Without the '.' your shell will look in your PATH variable (which you can see by running echo $PATH to see if the command you typed lives in any of the folders on your PATH. If it doesn't (as is the case with manage.py) it says it can't find the file. It is considered bad practice to include the current directory on your PATH, which is explained reasonably well here: http://www.faqs.org/faqs/unix-faq/faq/part2/section-13.html
On *nix, unlike Windows, the current directory is usually not in your $PATH variable. So the current directory is not searched when executing commands. You don't need ./ for running applications because these applications are in your $PATH; most likely they are in /bin or /usr/bin.
This question already has some awesome answers, but I wanted to add that, if your executable is on the PATH, and you get very different outputs when you run
./executable
to the ones you get if you run
executable
(let's say you run into error messages with the one and not the other), then the problem could be that you have two different versions of the executable on your machine: one on the path, and the other not.
Check this by running
which executable
and
whereis executable
It fixed my issues...I had three versions of the executable, only one of which was compiled correctly for the environment.
Rationale for the / POSIX PATH rule
The rule was mentioned at: Why do you need ./ (dot-slash) before executable or script name to run it in bash? but I would like to explain why I think that is a good design in more detail.
First, an explicit full version of the rule is:
if the path contains / (e.g. ./someprog, /bin/someprog, ./bin/someprog): CWD is used and PATH isn't
if the path does not contain / (e.g. someprog): PATH is used and CWD isn't
Now, suppose that running:
someprog
would search:
relative to CWD first
relative to PATH after
Then, if you wanted to run /bin/someprog from your distro, and you did:
someprog
it would sometimes work, but others it would fail, because you might be in a directory that contains another unrelated someprog program.
Therefore, you would soon learn that this is not reliable, and you would end up always using absolute paths when you want to use PATH, therefore defeating the purpose of PATH.
This is also why having relative paths in your PATH is a really bad idea. I'm looking at you, node_modules/bin.
Conversely, suppose that running:
./someprog
Would search:
relative to PATH first
relative to CWD after
Then, if you just downloaded a script someprog from a git repository and wanted to run it from CWD, you would never be sure that this is the actual program that would run, because maybe your distro has a:
/bin/someprog
which is in you PATH from some package you installed after drinking too much after Christmas last year.
Therefore, once again, you would be forced to always run local scripts relative to CWD with full paths to know what you are running:
"$(pwd)/someprog"
which would be extremely annoying as well.
Another rule that you might be tempted to come up with would be:
relative paths use only PATH, absolute paths only CWD
but once again this forces users to always use absolute paths for non-PATH scripts with "$(pwd)/someprog".
The / path search rule offers a simple to remember solution to the about problem:
slash: don't use PATH
no slash: only use PATH
which makes it super easy to always know what you are running, by relying on the fact that files in the current directory can be expressed either as ./somefile or somefile, and so it gives special meaning to one of them.
Sometimes, is slightly annoying that you cannot search for some/prog relative to PATH, but I don't see a saner solution to this.
When the script is not in the Path its required to do so. For more info read http://www.tldp.org/LDP/Bash-Beginners-Guide/html/sect_02_01.html
All has great answer on the question, and yes this is only applicable when running it on the current directory not unless you include the absolute path. See my samples below.
Also, the (dot-slash) made sense to me when I've the command on the child folder tmp2 (/tmp/tmp2) and it uses (double dot-slash).
SAMPLE:
[fifiip-172-31-17-12 tmp]$ ./StackO.sh
Hello Stack Overflow
[fifi#ip-172-31-17-12 tmp]$ /tmp/StackO.sh
Hello Stack Overflow
[fifi#ip-172-31-17-12 tmp]$ mkdir tmp2
[fifi#ip-172-31-17-12 tmp]$ cd tmp2/
[fifi#ip-172-31-17-12 tmp2]$ ../StackO.sh
Hello Stack Overflow
If some of my libraries locate out of default directory lib, could I indicate the require path to compile successfully without lib directory nor shards.yml.
Yes, change the CRYSTAL_PATH environment variable. By default it's $CRYSTAL_ROOT/src:lib (the src directory of the installation, and then the relative lib directory). Just add :some_other_dir at the end of that.
Example: CRYSTAL_PATH=$CRYSTAL_ROOT/src:lib:~/my_lib_dir
It didn't work as mentioned in another answer, this won't work CRYSTAL_PATH=$CRYSTAL_ROOT/src:lib:~/my_lib_dir.
Because in my case the CRYSTAL_ROOT was blank.
The solution was to execute crystal env and copy from there whatever paths it has for CRYSTAL_PATH and then re-set it as CRYSTAL_PATH=whatever-paths-you-just-copied:~/my_lib_dir
When I build, it succeeds with no errors. However, when I run from the IDE, I get an error (my image fails to load because it cannot find the directory).
However, if I go into the folder and run the program(.exe) it finds the image directory perfectly.
mTextures.Load(Textures::Background, "../GFX/Background.png");
^the line of code giving the directory.
I assume this is a problem with a setting I didn't enter correctly in my compiler?
I am using Code::Blocks on Windows.
Your debugger's current directory (i.e. the current directory used when you execute the application from within codeblock) is probably incorrect. Check your project settings, and fix the current directory to your target directory (the one which contains the executable itself).
Specific instructions are here.
It's because you're using a relative path in your file name:
"../GFX/Background.png"
the .. is saying "go up one directory form the current directory". If you want to be able to run your program anywhere, use an absolute path, something like:
"/home/me/GFX/Background.png"
Add the full path where the image exist with double slash.
mTextures.Load(Textures::Background, "C:\\Program Files\\..\\..\\GFX\\Background.png");
I'm (slowly!) working my way through the Django tutorial, and I've reached the point in Part 2 where I'm supposed to set the template_dir. I'm on a Mac (at work) where my user profile resides on a server, and I can't figure out how to set the path.
The tutorial files are in a folder called "tutorialshell", inside a folder called "Django," which is a first-level file inside my user folder "mattshepherd". That folder is the native folder when I launch the Terminal, for instance: it always starts me inside "mattshepherd".
I've tried
"~/Django/tutorialshell/templates"
and
"home/Django/tutorialshell/templates"
with no luck so far. I imagine there's some trick to doing this, as the files I'm trying to link to are on the network drive in my user folder, not on my local hard drive. Advice?
You want the absolute, not relative path. If you go to ~/Django/tutorialshell/templates in your terminal and then type pwd, it will tell you the full path to that folder. That's the value you should enter for the path.
Also: I assume you're actually talking about TEMPLATE_DIRS? If so, keep in mind that it's a list of paths, so it should look like:
TEMPLATE_DIRS = (
"/path/to/Django/tutorialshell/templates", # don't forget that trailing comma!
)
/Users/mattshepherd/Django/tutorialshell/templates
Please keep in mind that there is a LIST of template directories as mentioned by Jordan. The above location should work. In mac the user home directories are located at /Users/ + yourusername
It might be /home/ if /Users/ does not work.
As others have said you need the absolute path. But i would really suggest you to use relative path. It will make your code much more flexible. There are many ways to do it, this is what i usually do:
import os
ROOT = os.path.abspath(os.path.dirname(__file__))
then for the templates just do:
os.path.join(ROOT, 'templates')
You said you are using a Mac but you can make your code even more flexible by replacing "//" with "/" in the case you are using windows.
This is workig:
I have my exe in the same directory as Images folder;
Main:
|-Images
|-cross_ball
|-frame.bmp
|-game.exe
I'm refering to frame.bmp in my game.exe.
This path is workig good: "Images\\cross_ball\\frame.bmp"
This is not working:
Exe is in bin folder. bin folder is in the same folder as Images folder;
Main:
|-Images
|-cross_ball
|-frame.bmp
|-bin
|-game.exe
This path is not working: "..\\Images\\cross_ball\\frame.bmp"
If "Images\cross_ball\frame.bmp" is working, then your app's current directory isn't the Images directory like you think it is. It must be one dir up for that to work. That would also explain why moving the exe to the bin directory fails.
Are you starting your app from a shortcut or in a debugger? Shortcuts and debuggers specify the app's current directory, which isn't necessarily the same directory the exe is in.
As an experiment, replace each \ by \\ and test again.
Back slash is generally used for escape sequences like '\n'.
By putting two of them together, the run time ought to change them into one.
"Images\\cross_ball\\frame.bmp"
It appears that your logic is fine. Are you sure your process hasn't changed the current working directory - i.e. Main/bin/ might not be your working directory when you go to make this change in the executable.