`chmod a+x` *modifies* the argument&#39;s mode while `chmod 755` *sets* it. Try both variants on something that has full or no permissions and you will notice the difference.

Yes - different

`chmod a+x` will add the exec bits to the file but will not touch other bits. For example file might be still unreadable to `others` and `group`.

`chmod 755` will always make the file with perms `755` no matter what initial permissions were.

This may or may not matter for your script.

Indeed there is.

`chmod a+x` is relative to the current state and just sets the `x` flag. So a 640 file becomes 751 (or 750?), a 644 file becomes 755.

`chmod 755`, however, sets the mask as written: `rwxr-xr-x`, no matter how it was before. It is equivalent to `chmod u=rwx,go=rx`.



I have Python 3 installed on Cygwin. However, I am unable to install Python 3 packages via `pip`. Is there a way to do this?

Installing Pip-3.2 on Cygwin

I don&#39;t understand the connection between generics and arrays.

I can create array reference with generic type:

    private E[] elements; //GOOD

But can&#39;t create array object with generic type:

    elements = new E[10]; //ERROR

But it works:

    elements = (E[]) new Object[10]; //GOOD

How to create a generic array?

This may sound silly, but I have a file/ script that need to run and in order to do it I must change it to become executable. I would want to use either `chmod a+x` or `chmod 755`. But is there a difference between using `chmod a+x` and `chmod 755`?


Difference between using &quot;chmod a+x&quot; and &quot;chmod 755&quot;

<p>This may sound silly, but I have a file/ script that need to run and in order to do it I must change it to become executable. I would want to use either <code>chmod a+x</code> or <code>chmod 755</code>. But is there a difference between using <code>chmod a+x</code> and <code>chmod 755</code>?</p>


I&#39;m currently using tmux with xterm-256color $TERM variable. When in bash under tmux, pressing home/end would insert tilde characters (~). Outside of tmux the home/end keys work fine. 

Using cat and tput, I could see that there was a mismatch between the generated and expected sequences:

    $ cat -v # pressing home, then end
    ^[[1~^[[4~
    $ tput khome | cat -v; echo
    ^[OH
    $ tput kend | cat -v; echo
    ^[OF

To fix this, I decided to add the following to my .bashrc:

    if [[ -n &quot;$TMUX&quot; ]]; then
        bind &#39;&quot;\e[1~&quot;:&quot;\eOH&quot;&#39;
        bind &#39;&quot;\e[4~&quot;:&quot;\eOF&quot;&#39;
    fi

That fixed the problem for bash, however in other readline programs, such as within a REPL such as ipython, it still inserts a tilde for home/end. 

Why exactly is this a problem in the first place? Why is the generated sequence different when I&#39;m inside tmux vs outside it? How can fix this so that it&#39;s not an issue in any programs?

Home/End keys do not work in tmux

I have a simple BASH command that looks like

    for i in `seq 2`; do echo $i; done; &gt; out.dat

When this runs the output of `seq 2` is output to the terminal and nothing is output to the data file (out.dat)

I am expecting standard out to be redirected to out.dat like it does simply running the command `seq 2 &gt; out.dat`



Redirecting output of bash for loop

I&#39;m trying to find a line in a file and replace the next line with a specific value. I tried sed, but it seems to not like the \n. How else can this be done?

The file looks like this:

    &lt;key&gt;ConnectionString&lt;/key&gt;
    &lt;string&gt;anything_could_be_here&lt;/string&gt;

And I&#39;d like to change it to this

    &lt;key&gt;ConnectionString&lt;/key&gt;
    &lt;string&gt;changed_value&lt;/string&gt;

Here&#39;s what I tried:

    sed -i &#39;&#39; &quot;s/&lt;key&gt;ConnectionString&lt;\/key&gt;\n&lt;string&gt;&lt;\/string&gt;/&lt;key&gt;ConnectionString&lt;\/key&gt;\n&lt;string&gt;replaced_text&lt;\/string&gt;/g&quot; /path/to/file

find matching text and replace next line

I have the following command in the part of a backup shell script:

    tar -cjf site1.bz2 /var/www/site1/

When I list the contents of the archive, I get:

    tar -tf site1.bz2
    var/www/site1/style.css
    var/www/site1/index.html
    var/www/site1/page2.html
    var/www/site1/page3.html
    var/www/site1/images/img1.png
    var/www/site1/images/img2.png
    var/www/site1/subdir/index.html

But I would like to remove the part `/var/www/site1` from directory and file names within the archive, in order to simplify extraction and avoid useless constant directory structure. Never know, in case I would extract backuped websites in a place where web data weren&#39;t stored under `/var/www`.

For the example above, I would like to have :

    tar -tf site1.bz2
    style.css
    index.html
    page2.html
    page3.html
    images/img1.png
    images/img2.png
    subdir/index.html

So, that when I extract, files are extracted in the current directory and I don&#39;t need to move extracted files afterwards, and so that sub-directory structures is preserved.

There are already many questions about tar and backuping in `stackoverflow` and at other places on the web, but most of them ask for dropping the entire sub-directory structure (flattening), or just add or remove the initial / in the names (I don&#39;t know what it changes exactly when extracting), but no more.

After having read some of the solutions found here and there as well as the manual, I tried :

    tar -cjf site1.bz2 -C . /var/www/site1/
    tar -cjf site1.bz2 -C / /var/www/site1/
    tar -cjf site1.bz2 -C /var/www/site1/ /var/www/site1/
    tar -cjf site1.bz2 --strip-components=3 /var/www/site1/

But none of them worked the way I want. Some do nothing, some others don&#39;t archive sub-directories anymore.

It&#39;s inside a backup shell script launched by a Cron, so I don&#39;t know well, which user runs it, what is the path and the current directory, so always writing absolute path is required for everything, and would prefer not changing current directory to avoid breaking something further in the script (because it doesn&#39;t only backup websites, but also databases, then send all that to FTP etc.)

How to achieve this?

Have I just misunderstood how the option -C works?



Tar a directory, but don&#39;t store full absolute paths in the archive

I’m following in [Generating SSH Keys][1], it says

&gt; ```sudo apt-get install xclip```
&gt;
 Downloads and installs xclip. If you don&#39;t have `apt-get`, you might need to use another installer (like `yum`)  
&gt;
&gt; ```xclip -sel clip &lt; ~/.ssh/id_rsa.pub```
&gt;
  Copies the contents of the id_rsa.pub file to your clipboard

But after I run`xclip -sel clip &lt; ~/.ssh/id_rsa.pub` I get `Error: Can&#39;t open display: (null)`
What is the problem? I googled around but found nothing about it

  [1]: https://help.github.com/articles/generating-ssh-keys#platform-linux

Error: Can&#39;t open display: (null) when using Xclip to copy ssh public key

In my bash script I do:

    mkdir product;

When I run the script more than once I get:

    mkdir: product: File exists

In the console.

So I am looking to only run mkdir if the dir doesn&#39;t exist.  Is this possible?

Only mkdir if it does not exist

What is the difference between assigning to a variable like `var=foo` and using let like `let var=foo`? Or cases like `var=${var}bar` and `let var+=bar`? What are the advantages and disadvantages of each approach?

Bash: let statement vs assignment

When I did `which groovy`, I got the below output:

    /usr/local/bin/groovy

So I went ahead and created a `helloworld.groovy` with the below content

    #!/usr/local/bin/groovy
    println &quot;hello world&quot;

After that I did `chmod +x helloworld.groovy` and attempted to run the file with `./hellworld.groovy` and sadly, I got this error `./helloworld.groovy: line 2: print: command not found`

I could get rid of the error by changing to

    #!/usr/bin/env groovy
    println &quot;hello world&quot;

Why would the first method cause the error?


Running Groovy script from the command line

Hi I have searched various forums and here as well, I could find some answers for Linux and Mac but not able to find solution for Unix and specially Korn Shell.

How to get process name (command name) from process id (pid)

Below reference I found from SO 
[This one ][1]
[And this one also][2]

I tried below command

  [1]: https://stackoverflow.com/questions/4189717/get-process-name-by-pid
  [2]: https://stackoverflow.com/questions/15545341/process-name-from-its-pid-in-linux

    ps -eaf | awk &#39;{ print substr($0, index($0, $9)) }&#39;

Above command is failing at a point where TIME is given rather than Month and Date (because in this case there will be only 8 columns in string)

Any suggestion would help.

How to get pid given the process name

In Bash, we can set an environment variable for a single command this way:

    FOO=bar somecommand

What if we want to *unset* a variable for a single command?

Unset an environment variable for a single command

How would I change all files to 644 and all folders to 755 using `chmod` from the `linux` command prompt? (Terminal)



Change all files and folders permissions of a directory to 644/755

why doesn&#39;t this work I am trying to change all files to 644 abd all -d to 755:

    find . -type f -exec chmod 644 {} ;

**i get: find: missing argument to `-exec&#39;**
 thanks

find . -type f -exec chmod 644 {} ;

The code bases I work with are checked out from Git repositories onto my Linux machine. Since our production code is written to be deployed on Linux, I do all the testing on my Linux machine but like to use Windows for everyday usage, including code editing/authoring. 

For that purpose, I have created a **Samba share** of the folder (my home folder) where I checkout the code to, like this:

    [wgrover]
        path = /home/wgrover
        available = yes
        valid users = wgrover
        read only = no
        browsable = yes
        public = yes
        writable = yes

However, when I edit a file from the samba share `\\linux-box\wgrover` in Windows, **the file permission in Linux keeps changing to `755` even though it was `644` before editing**. 

This keeps showing up in my `git diff` like this:

    diff --git a/debian/maggie.nginx.conf b/debian/maggie.nginx.conf
    old mode 100644
    new mode 100755
    index 7cda506..7eab574

It is possible to set a `create mask` in smb.conf but that will also not  &quot;preserve&quot; the original file permissions. I can ignore file mode changes in git by setting `fileMode = false` in `.gitconfig` but that also ignores the problem.

***Is there any way to preserve the file permissions when they are modified from linux?***

preserving file permissions for samba shares when file is edited

I have a folder in my subdomain which is created through WHM so the owner of that subdomain is not the owner of main domain. 

I want to change the owner of one of the folders of subdomain to domain owner. I tried this, but when I check with `winscp` it shows owner as 500.

  
      chown users:user /home/xyz/somnething/photo/

I&#39;ve tried to change from winscp also, but there is no option for winscp, so I&#39;ve logged in as root using putty and ran the command from above, but it doesn&#39;t help and I am unable to upload any file to subdomain from the main domain, as it returns error &quot;permission denied&quot;.


    $ ls -l /home/xyz/somnething/photo/
    total 8 
    drwxr-xr-x 2 sujit sujit 4096 Feb 21 23:39 ./ 
    drwxr-x--- 5 rohan nobody 4096 Feb 22 02:28 ../ 

I want to give the ownership of rohan to sujit to have rights to upload file from sujit domain to subdomain rohan

**Update:**

Now it is changing owner to 500 

changing the owner of folder in linux

Running bash on windows 10, the simple syntax below works when I SSH to my webserver, but not when I exit out and am on my local machine. It doesn&#39;t give me an error, but I can see permissions are unchanged. I have to checked that I am set up as an administrator on my computer. Is this an error or is this just a consequence of the local operating system being windows? IF the later, it makes me question the value of using bash on windows if common operations such as this won&#39;t work. 

    $chmod 644 filename 

 

Content Type	Original Author	Original Content on Stackoverflow
Question	user2579439	View Question on Stackoverflow
Solution 1 - Linux	filmor	View Answer on Stackoverflow
Solution 2 - Linux	akostadinov	View Answer on Stackoverflow
Solution 3 - Linux	glglgl	View Answer on Stackoverflow

Difference between using "chmod a+x" and "chmod 755"

Linux Problem Overview

Linux Solutions

Solution 1 - Linux

Solution 2 - Linux

Solution 3 - Linux

How to create a generic array?

Installing Pip-3.2 on Cygwin

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