I am using the 2003 textbook - http://www.amazon.com/Unix-Shell-Programming-3rd-Edition/dp/0672324903
My OS is linux L-ubuntu 13 which is not based on POSIX (I think)
It says that I can store who | wc -l in a file called nu and then execute nu. But, before that I need to make this file executable by using chmod +x file(s). This does not work. How do I make the nu "command" work ? I know I can do it by naming nu as nu.sh and then doing bash nu.sh, but I want to try this way also.
To execute a file that is not in the PATH, you must give a properly qualified directory name. While giving the name of the file in the current directory is sufficient as an argument to a program, in order to execute a shell script or other executable file, you must give at least a relative path. For example, if the file is in your home directory, which is also the working directory, any of the following are acceptable:
./nu
~/nu
/home/username/nu
However, simply nu will only attempt to search the PATH, which probably includes places such as /bin, /usr/bin, and so on.
Related
About a year ago, I created a couple text files called "compile" and "pull." When I go into a cygwin prompt and type those names and hit enter (basically use them as a command), the cygwin terminal runs what is in those text files. For instance here is the contents of one:
git checkout master
git checkout -- .
I don't even remember how I did this. I'm pretty sure this is not a bash script.
I do remember that I had to not just create the file in notepad but also perform some linux command line operation on it, in order to use it. Once I did that I could basically use the file as a command.
In *nix, you have to make a file executable in order to be able to run it:
chmod u+x file
You also need to add the path to the file to the PATH variable
PATH=$PATH:/path/to/the/file
or, add . to always scan the current directory for commands (it's considered unsecure, though):
PATH=$PATH:.
I have a Tcl script that works on Windows. When I run it and pass in file names when prompted, usually with a relative directory path. On Windows the script will take absolute OR relative directory paths ... it works, no problems at all.
On Linux it will NOT work in the same way. It will only work if I spell out the full file path, e.g. /home/gxuser/input/test.txt ... It will NOT take relative directory paths like ./input/test.txt
By "work" I mean it should OPEN the file ... It is there and the permissions are fine.
On Linux the program fails with the following error:
couldn't open "./input/test.txt": no such file or directory
while executing
"open $upload r"
The offending line in the code is:
set infile [open $upload r]
What am I doing wrong? I presume, I have overlooked some nuance of the Tcl language, and assumed it should recognize relative paths.
Relevant information:
% puts $tcl_version
8.4
% info patchlevel
8.4.19
% uname -a
Linux gxengine 2.6.32-60-generic #122-Ubuntu SMP
It is possible that a function you call is changing the current working directory. There is no way to tell which one that could be without inspecting the code, but you can check if this is the case by displaying [pwd] before calling open.
Another way things could go wrong is by the script being started in different ways from Unix and Windows - e.g. by shortcut on Windows and from the command line off the PATH on Unix.
Where you have filenames passed in by the user and you can't be sure that code you call won't cd under your feet, you're advised to process the filenames into absolute filenames as soon as possible in your script, possibly even before any package require or source calls.
This is actually easy to do.
set absoluteFilename [file normalize $userProvidedFilename]
As long as this is done before the first cd (or chdir()/SetCurrentDirectory() at the C/C++ level) future changes of directory will not break the path. The script must be prepared to work with absolute filenames, but that's easily done.
You can turn a relative path into an absolute path with respect to any arbitrary directory with file join:
set filename [file join [file normalize $arbitraryLocation] $relativeFilename]
(The file join is smarter than just inserting a directory separator.)
I want to add a small script to the linux PATH so I don't have to actually run it where it's physically placed on disk.
The script is quite simple is about giving apt-get access through a proxy I made it like this:
#!/bin/bash
array=( $# )
len=${#array[#]}
_args=${array[#]:1:$len}
sudo http_proxy="http://user:password#server:port" apt-get $_args
Then I saved this as apt-proxy.sh, set it to +x (chmod) and everything is working fine when I am in the directory where this file is placed.
My question is : how to add this apt-proxy to PATH so I can actually call it as if it where the real apt-get ? [from anywhere]
Looking for command line only solutions, if you know how to do by GUI its nice, but not what I am looking for.
Try this:
Save the script as apt-proxy (without the .sh extension) in some directory, like ~/bin.
Add ~/bin to your PATH, typing export PATH=$PATH:~/bin
If you need it permanently, add that last line in your ~/.bashrc. If you're using zsh, then add it to ~/.zshrc instead.
Then you can just run apt-proxy with your arguments and it will run anywhere.
Note that if you export the PATH variable in a specific window it won't update in other bash instances.
You want to define that directory to the path variable, not the actual binary e.g.
PATH=$MYDIR:$PATH
where MYDIR is defined as the directory containing your binary e.g.
PATH=/Users/username/bin:$PATH
You should put this in your startup script e.g. .bashrc such that it runs each time a shell process is invoked.
Note that order is important, and the PATH is evaluated such that if a script matching your name is found in an earlier entry in the path variable, then that's the one you'll execute. So you could name your script as apt-get and put it earlier in the path. I wouldn't do that since it's confusing. You may want to investigate shell aliases instead.
I note also that you say it works fine from your current directory. If by that you mean you have the current directory in your path (.) then that's a potential security risk. Someone could put some trojan variant of a common utility (e.g. ls) in a directory, then get you to cd to that directory and run it inadvertently.
As a final step, after following the solution form proposed by #jlhonora (https://stackoverflow.com/a/20054809/6311511), change the permissions of the files in the folder "~/bin". You can use this:
chmod -R 755 ~/bin
make an alias to the executable into the ~/.bash_profile file and then use it from anywhere or you can source the directory containing the executables you need run from anywhere and that will do the trick for you.
adding to #jlhonora
your changes in ~./bashrc or ~./zshrc won't reflect until you do
source ~./zshrc or source ./bashrc , or restart your pc
Here is my problem,
In Windows I am making a zip file in which there is a text .sh file which is supposed to be executed in Linux.
The user on the other end opens the zip file in Linux and tries to execute the .sh file but the execute permission is gone. So the user has to do it manually ( like explained here:add execute permission.
How can I in Windows make the .sh executable and add it to a zip file so that when the zip file opens in linux the .sh file still retains its execute permission ( so that user doesn't have to do it manually)
As far as I know the permission system in Linux is set up in such a way to prevent exactly what you are trying to accomplish.
I think the best you can do is to give your Linux user a custom unzip one-liner to run on the prompt:
unzip zip_name.zip && chmod +x script_name.sh
If there are multiple scripts that you need to give execute permission to, write a grant_perms.sh as follows:
#!/bin/bash
# file: grant_perms.sh
chmod +x script_1.sh
chmod +x script_2.sh
...
chmod +x script_n.sh
(You can put the scripts all on one line for chmod, but I found separate lines easier to work with in vim and with shell script commands.)
And now your unzip one-liner becomes:
unzip zip_name.zip && source grant_perms.sh
Note that since you are using source to run grant_perms.sh, it doesn't need execute permission
The ZIP file format does allow to store the permission bits, but Windows programs normally ignore it.
The zip utility on Cygwin however does preserve the x bit, just like it does on Linux.
If you do not want to use Cygwin, you can take a source code and tweak it so that all *.sh files get the executable bit set.
Or write a script like explained here
This is possible using the Info-Zip open-source Zip utilities. If unzip is run with the -X parameter, it will attempt to preserve the original permissions. If the source filesystem was NTFS and the destination is a Unix one, it will attempt to translate from one to the other. I do not have a Windows system available right now to test the translation, so you will have to experiment with which group needs to be awarded execute permissions. It'll be something like "Users" or "Any user"
Use my windows command line utility zip_exec.zip to set the executable flag for linux/unix and mac (tested on files created with Windows Explorer and 7zip). The cpp source is also available. I searched the internet a lot before making my own utility. It can be modified to set any file attribute.
This is not possible. Linux permissions and windows permissions do not translate. They are machine specific. It would be a security hole to allow permissions to be set on files before they even arrive on the target system.
I have a file called x.sh that I want to execute. If I run:
x.sh
then I get:
x.sh: command not found
If I run:
./x.sh
then it runs correctly. Why do I have to type in ./ first?
Because the current directory is not into the PATH environment variable by default, and executables without a path qualification are searched only inside the directory specified by PATH. You can change this behavior by adding . to the end of PATH, but it's not common practice, you'll just get used to this UNIXism.
The idea behind this is that, if executables were searched first inside the current directory, a malicious user could put inside his home directory an executable named e.g. ls or grep or some other commonly used command, tricking the administrator to use it, maybe with superuser powers. On the other hand, this problem is not much felt if you put . at the end of PATH, since in that case the system directories are searched first.
But: our malicious user could still create his dangerous scripts named as common typos of often used commands, e.g. sl for ls (protip: bind it to Steam Locomotive and you won't be tricked anyway :D).
So you see that it's still better to be safe that, if you type an executable name without a path qualification, you are sure you're running something from system directories (and thus supposedly safe).
Because the current directory is normally not included in the default PATH, for security reasons: by NOT looking in the current directory all kinds of nastiness that could be caused by planting a malicious program with the name of a legitimate utility can be avoided. As an example, imagine someone manages to plant a script called ls in your directory, and that script executes rm *.
If you wish to include the current directory in your path, and you're using bash as your default shell, you can add the path via your ~/.bashrc file.
export PATH=$PATH:.
Based on the explanation above, the risk posed by rogue programs is reduced by looking in . last, so all well known legitimate programs will be found before . is checked.
You could also modify the systemwide settings via /etc/profile but that's probably not a good idea.
Because current directory is not in PATH (unlike cmd in Windows). It is a security feature so that malicious scripts in your current directory are not accidentally run.
Though it is not advisable, to satisfy curiosity, you can add . to the PATH and then you will see that x.sh will work.
If you don't explicitly specify a directory then the shell searches through the directories listed in your $PATH for the named executable. If your $PATH does not include . then the current directory is not searched.
$ echo $PATH
/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin
This is on purpose. If the current directory were searched then the command you type could potentially change based on what directory you're in. This would allow a malicious user to place a binary named ls or cp into directories you frequent and trick you into running a different program.
$ cat /tmp/ls
rm -rf ~/*
$ cd /tmp
$ ls
*kaboom*
I strongly recommend you not add . to your $PATH. You will quickly get used to typing ./, it's no big deal.
You can't execute your file by typing simply
x.sh
because the present working directory isn't in your $PATH. To see your present working directory, type
$ pwd
To see your $PATH, type
$ echo $PATH
To add the current directory to your $PATH for this session, type
$ PATH=$PATH:.
To add it permanently, edit the file .profile in your home directory.