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
Trying to learn more about the many mysteries of bash.
I have neovim installed. I have nvim aliased to vim. I have nvim configured to use my vim config.
Let's say I want to use the real vim command, though. which vim yields "/usr/local/bin/vim".
But calling /usr/local/bin/vim directly results in the error given in the title. Why is that? How can I run my vim command directly?
From the result of the file command it seems that the file in /usr/local/bin/vim is somehow broken (the system doesn't recognize it as an elf file).
The file command should identify any executable file with the file format (and other types of files). When this command returns output of data it means that it couldn't identify the file at all.
Since you found the vim executable in Cellar/vim/8.1.1000/bin/vim, you can use this file instead of file which is in /usr/local/bin/vim, or you can create the link by yourself, that should fix this error.
If you would create the link with absolute path instead of relative path, it should work.
I am very new to bash and using .sh files. I am trying to run the program aescrypt by calling it in a .sh file as follows (aescrypt is in the same directory as the .sh file) :
./aescrypt -e -p password file.txt
It throws the following error:
./aescrypt no such file or directory
Am I doing it wrong?
ps- I realy don't want to add it to the PATH variable as I will be using this on more than one computer that resets every day.
The location of the script is irrelevant. The thing that matters is the working directory of the process executing the script. The simplest solution really is to add aescrypt to a standard location like /bin or /usr/bin. If neither of those is acceptable, perhaps /usr/local/bin is an option. Otherwise, just use the full path of aescrypt in your script. Either hard code it, or if it is in the same directory as the script, try:
$(dirname $0)/aescrypt ...
(Note that hardcoding is more reliable, but less flexible. If you move the executable, the script will break. But using dirname will break if the script changes directory during execution.)
how about if you call the program like ./aescrypt.sh, thats the way to call an .sh programm througt the terminal
First off all, you have also to change the permissions of the file to make it executable, the way to make that is to write in the terminal, the command:
sudo chmod 765 aescrypt.sh
For that you have to be located where the file is
On the Windows command line and cygwin bash I can execute the following without problems:
cvs login
cvs -Q log -N -rVersion_01_00
A ruby script in the same directory contains the following:
`cvs login`;
`cvs -Q log -N -rVersion_01_00`;
When I execute the ruby script on the Windows command line I get the following error:
cvs log: warning: failed to open /cygdrive/c/Documents and Settings/za100744/.cvspass for reading: No such file or directory
If I run the script in a cygwin bash shell I get the same output I would as when I type in the commands manually.
I have no idea as to what is going wrong. The path generated by the Ruby script is wrong since it is a cygwin path but it works correctly directly on the command line. I use cvs that came as part of cygwin:
which cvs
cvs is an external : C:\cygwin\bin\cvs.exe
Ruby is the one-click installer version:
which ruby
/cygdrive/c/Ruby/bin/ruby
It seems like cvs under Ruby can not resolve /cygdrive/c to c: but works OK from the cmdline.
Perl gives me exactly the same problem.
my $str = "cvs -Q log -N -r$cvs_tag|";
open(CVS_STATUS, $str) or die "\n##ERROR##";
It looks like either CVS can't create the file, or your path is wrong. Does the file .cvspass exist? If not, this page suggests you try creating an empty .cvspass file and then run your command. e.g. do
touch ~/.cvspass
If this doesn't help, then the problem is probably path related. There are a few possibilities; $HOME not set correctly, your home dir not matching what's in \etc\passwd, etc. See this tutorial for some troubleshooting steps that should help pin down the problem.
Using a windows native compiled CVS solves the problem. It is not ideal since I have to send a cvs executable with the script for users that has cygwin CVS but its better than nothing.
We had several problems with unix-, mixed- and windows-style paths in cygwin based perl scripts and built-in tools such as rsync. E.g. rsync can't handle wind-style paths. Use the tool "cygpath.exe" to adjust them correctly. Maybe it's the cause.
I'm trying to parse a MYSQL slow query log from the command line.
Upon entering this:
set PATH=G:\xampp\perl\bin\;%PATH%
cd /d G:\xampp\mysql\scripts
perl mysqldumpslow.pl -s c -t 10
The shell returns an error can't locate strict.pm in #INC (#INC contains: .) at mysqldumpslow.pl at line 8. BEGIN failed
In the perl directory in xampp, there is only one file perl.exe.
Am I missing perl modules/libraries? What do I need to read this log file?
A workaround is to find the location of strict.pm in your perl installation and to add the directory to the PERL5LIB environment variable, or to invoke perl with the
-I/path/to/strict.pm/directory option (see perlfaq8: How do I add a directory to my include path (#INC) at runtime?).
If you find more unsatisfied dependencies, keep adding directories to PERL5LIB or with additional -I options until your program can run.
(Though eventually you will probably get tired of this and fix/reinstall perl.)
UPDATE: Looking through the 1.7.3 XAMPP distribution, all of the perl library files are located under xampp\perl\lib and xampp\perl\site\lib, so
perl -IG:/xampp/perl/lib -IG:/xampp/perl/site/lib mysqldumpslow.pl -s c -t 10
is probably all that you need to do. YMMV if you have an older XAMPP distribution.
Your Perl installation seems to have been messed up in one way or another. I am not familiar with xampp, but I have a hard time believing they bundled just the perl.exe without the rest of the distribution.
Under G:\xampp\perl, there should be subdirectories such as lib, site etc.
strict is a core pragma and its absence indicates that you do not have a proper Perl installation.
In fact, I just downloaded xampp and it does contain lib and site\lib under xampp\perl (it is missing the documentation, but that is not essential to running Perl scripts).