Bash maintains a number of variables including `BASH_SOURCE` which is an array of source file pathnames.

`${}` acts as a kind of quoting for variables.

`$()` acts as a kind of quoting for commands but they&#39;re run in their own context.

`dirname` gives you the path portion of the provided argument.

`cd` changes the current directory.

`pwd` gives the current path.

`&amp;&amp;` is a logical `and` but is used in this instance for its side effect of running commands one after another.

In summary, that command gets the script&#39;s source file pathname, strips it to just the path portion, `cd`s to that path, then uses `pwd` to return the (effectively) full path of the script. This is assigned to `DIR`. After all of that, the context is unwound so you end up back in the directory you started at but with an environment variable `DIR` containing the script&#39;s path.

How do I install RubyGems on my Mac?

I tried to run `$ gem install rubygems-update` with no luck . It returns

    ERROR:  While executing gem ... (Gem::FilePermissionError)
        You don&#39;t have write permissions for the /Library/Ruby/Gems/2.0.0 directory.

Any help would be great. Thanks

How do I install ruby gems on Mac

I use [History][1] package to redirect invalid URL to 404 page on my react component.

I use `.replace` instead of `.push` simply because I don&#39;t want the browser to record any invalid url I have visited.

Have I missed the point here? And is there a trade-off between choosing one or the other for my purpose?

Can someone explain to me? thanks in advance ;)


  [1]: https://github.com/mjackson/history

What is the trade off between history push and replace?

I need to get the path of the script. I can do that using `pwd` if I am already in the same directory, I searched online and I found this 

`DIR=&quot;$( cd &quot;$( dirname &quot;${BASH_SOURCE[0]}&quot; )&quot; &amp;&amp; pwd )&quot;` 

But I don&#39;t know how to use that.



DIR=&quot;$( cd &quot;$( dirname &quot;${BASH_SOURCE[0]}&quot; )&quot; &amp;&amp; pwd )&quot; How does that work?

I need to get the path of the script. I can do that using <code>pwd</code> if I am already in the same directory, I searched online and I found this
<code>DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" &#x26;&#x26; pwd )"</code>
But I don't know how to use that.

I have a Bash script that creates a *.tar.gz* file, encrypts, and then sends it to a drive. However, I cannot open the *.tar.gz* file afterwards. Here is my process...

Bash script that encrypts.

```lang-none
#!/bin/sh

# Tar the automysqlbackup directory
tar -zcf &quot;red-backup-$(date &#39;+%Y-%m-%d&#39;).tar.gz&quot; /var/lib/automysqlbackup/

# Encrypt the tar file
openssl aes-256-cbc -a -salt -in &quot;red-backup-$(date &#39;+%Y-%m-%d&#39;).tar.gz&quot; -out &quot;red-backup-$(date &#39;+%Y-%m-%d&#39;).tar.gz.enc&quot; -pass &#39;pass:MySecretPWD&#39;

# Remove the original tar file
rm -rf &quot;red-backup-$(date &#39;+%Y-%m-%d&#39;).tar.gz&quot;

# Upload to Google Drive
gdrive upload --file &quot;red-backup-$(date &#39;+%Y-%m-%d&#39;).tar.gz.enc&quot; -p &quot;jofhriout849uioejfoiu09&quot;
```

Then I download the file and use

```lang-none
sudo openssl aes-256-cbc -e -in red-backup-2016-09-22.tar.gz.enc -out red-backup-2016-09-22.tar.gz
```

I then enter the passphrase for my file twice and I now get a file called

```lang-none
red-backup-2016-09-22.tar.gz
```

When I then try

```lang-none
sudo tar -zxvf red-backup-2016-09-22.tar.gz
```

I get

```lang-none
gzip: stdin: not in gzip format
tar: Child returned status 1
tar: Error is not recoverable: exiting now
```

I have also tried renaming the file .tar and also tried

```lang-none
sudo tar xvf red-backup-2016-09-22.tar.gz
```

and

```lang-none
sudo tar xvf red-backup-2016-09-22.tar

tar: This does not look like a tar archive
tar: Skipping to next header
tar: Exiting with failure status due to previous errors
```

Where am I going wrong?





gzip: stdin: not in gzip format tar: Child returned status 1 tar: Error is not recoverable: exiting now

I&#39;m trying to call native machine-language code. Here&#39;s what I have so far (it gets a bus error):

    char prog[] = {&#39;\xc3&#39;}; // x86 ret instruction

    int main()
    {
        typedef double (*dfunc)();

        dfunc d = (dfunc)(&amp;prog[0]);
        (*d)();
        return 0;
    }

It does correctly call the function and it gets to the ret instruction.  But when it tries to execute the ret instruction, it has a SIGBUS error.  Is it because I&#39;m executing code on a page that is not cleared for execution or something like that?

So what am I doing wrong here? 

How to call machine code stored in char array?

I&#39;m using arch linux and I&#39;ve installed Anaconda as per the instruction on the Anaconda site. When I&#39;m attempting to run `conda info --envs
` I get the following error:

&gt; bash: /home/lukasz/anaconda3/bin/conda:
&gt; /opt/anaconda1anaconda2anaconda3/bin/python: bad interpreter: No such
&gt; file or directory

I&#39;ve tried looking for the directory `/opt/anaconda1anaconda2anaconda3/bin/python:` but it simply doesn&#39;t exist. 

Furthermore, when I run python from the terminal it runs as normal with the following displayed at the top

    Python 3.5.2 |Anaconda custom (64-bit)| (default, Jul  2 2016, 17:53:06) 
    [GCC 4.4.7 20120313 (Red Hat 4.4.7-1)] on linux
    Type &quot;help&quot;, &quot;copyright&quot;, &quot;credits&quot; or &quot;license&quot; for more information.

for completeness my `.bashrc` file resembles:

    #
    # ~/.bashrc
    #

    # If not running interactively, don&#39;t do anything
    [[ $- != *i* ]] &amp;&amp; return

    alias ls=&#39;ls --color=auto&#39;
    PS1=&#39;[\u@\h \W]\$ &#39;

    # added by Anaconda3 4.0.0 installer
    export PATH=&quot;/home/lukasz/anaconda3/bin:$PATH&quot;

    # python startup for up keys
    export PYTHONSTARTUP=$HOME/.pythonstartup

I&#39;ve tried following [this](https://stackoverflow.com/questions/35246386/conda-command-not-found) and making the the appropriate changes but nothing, I&#39;ve also attempted to do [this](https://stackoverflow.com/questions/33946829/conda-command-not-found-path-is-in-bashrc) but there really isn&#39;t a solution posted. 

I would like to try to fix this without having to remove Anaconda and reinstalling it.

conda command will prompt error: &quot;Bad Interpreter: No such file or directory&quot;

I&#39;m working with QT and embedded devices and in many documentation items ( [like here][1]) they are talking about sysroots. I&#39;ve searched the web but I couldn&#39;t find anything about what a sysroot is. I have a cross-compiler-toolchain though. What&#39;s a sysroot and how do I create one ?


  [1]: http://doc.qt.io/QtQuick2DRenderer/qtquick2drenderer-installation-guide.html

What is a sysroot exactly and how do I create one ?


I have a boto3 client :

    boto3.client(&#39;kms&#39;)

But it happens on new machines, They open and close dynamically. 


        if endpoint is None:
            if region_name is None:
                # Raise a more specific error message that will give
                # better guidance to the user what needs to happen.
                raise NoRegionError()


Why is this happening? and why only part of the time?



boto3 client NoRegionError: You must specify a region error only sometimes

I am making a NW.js app on Mac, and want to run the app in dev mode by double-clicking on an icon. First step, I&#39;m trying to make my shell script work.

Using VSCode on Windows (I wanted to gain time), I have created a `run-nw` file at the root of my project, containing this:

    #!/bin/bash
    
    cd &quot;src&quot;
    npm install
    
    cd ..
    ./tools/nwjs-sdk-v0.17.3-osx-x64/nwjs.app/Contents/MacOS/nwjs &quot;src&quot; &amp;

but I get this output:

    $ sh ./run-nw
    
    : command not found  
    : No such file or directory  
    : command not found  
    : No such file or directory  
    
    Usage: npm &lt;command&gt;
    
    where &lt;command&gt; is one of:  (snip commands list)
    
    (snip npm help)
    
    npm@3.10.3 /usr/local/lib/node_modules/npm  
    : command not found  
    : No such file or directory  
    : command not found

I really don&#39;t understand:

* it seems that it takes empty lines as commands. In my editor (VSCode) I have tried to replace `\r\n` with `\n` (in case the `\r` creates problems) but it changes nothing.
* it seems that it doesn&#39;t find the folders (with or without the `dirname` instruction), or maybe it doesn&#39;t know about the `cd` command ?
* it seems that it doesn&#39;t understand the `install` argument to `npm`
* the part that really weirds me out, is that it still runs the app (if I did a `npm install` manually)...

Not able to make it work properly, and suspecting something weird with the file itself, I created a new one directly on the Mac, using vim this time. I entered the exact same instructions, and... now it works without any issue.  
A diff on the two files reveals exactly zero difference.

What can be the difference? What can make the first script not work? How can I find out?


## Update

Following the accepted answer&#39;s recommendations, after the wrong line endings came back, I checked multiple things. It turns out that since I copied my `~/.gitconfig` from my Windows machine, I had `autocrlf=true`, so every time I modified the bash file under Windows, it re-set the line endings to `\r\n`.  
So, in addition to running `dos2unix` (which you will have to install using Homebrew on a Mac), if you&#39;re using Git, check your config.


Are shell scripts sensitive to encoding and line endings?

When using Psql in Linux, if the result of my SQL query contains many columns or long strings of data, it will wrap the initial view and only once I scroll to the side will it stop wrapping and show each row on a separate line.

I&#39;ve tried various [`\pset` options][1] such as `format unaligned`, `format aligned`, `format wrapped`, `columns 0`, `columns 1000`, but none seemed to *fully* stop wrapping unless I generate static output to a file.

How can I set it to never wrap the output while still being scrollable and showing the result using the default ascii table format?


  [1]: https://www.postgresql.org/docs/9.2/static/app-psql.html

Disable wrapping in Psql output

I have written a script to retrieve certain value from `file.json`. It works if I provide the value to jq `select`, but the variable doesn&#39;t seem to work (or I don&#39;t know how to use it).

    #!/bin/sh

    #this works ***
    projectID=$(cat file.json | jq -r &#39;.resource[] | select(.username==&quot;myemail@hotmail.com&quot;) | .id&#39;)
    echo &quot;$projectID&quot;

    EMAILID=myemail@hotmail.com

    #this does not work *** no value is printed
    projectID=$(cat file.json | jq -r &#39;.resource[] | select(.username==&quot;$EMAILID&quot;) | .id&#39;)
    echo &quot;$projectID&quot;

Passing bash variable to jq

How do I print the environment variable just being set?

    NAME=sam echo &quot;$NAME&quot; # empty

You can see here using `eval` it works. Is this the way?

    NAME=sam eval &#39;echo $NAME&#39; # =&gt; sam

How to print / echo environment variables?

I&#39;d like to write a shell script which checks if a certain file, `archived_sensor_data.json`, exists, and if so, deletes it. Following http://www.cyberciti.biz/tips/find-out-if-file-exists-with-conditional-expressions.html, I&#39;ve tried the following:

    [-e archived_sensor_data.json] &amp;&amp; rm archived_sensor_data.json

However, this throws an error

    [-e: command not found

when I try to run the resulting `test_controller` script using the `./test_controller` command. What is wrong with the code?

How to check if a file exists in a shell script

I am writing a shell script in OSX(unix) environment. I have a file called `test.properties` with the following content:

`cat test.properties` gets the following output:

    //This file is intended for 
    //blah blah purposes
    123

Using `cat` command, how can I get only the last line of the file ?

How to get the last line of a file using cat command

right now I am using a shell script in ansible that would be much more readable if it was on multiple lines


    - name: iterate user groups
      shell: groupmod -o -g {{ item[&#39;guid&#39;] }} {{ item[&#39;username&#39;] }} ....more stuff to do
      with_items: &quot;{{ users }}&quot;


Just not sure how to allow multiline script in Ansible shell module 

How to do multiline shell script in Ansible

I have a sample `sh` script on my Linux environment, which basically run&#39;s the `ssh-agent` for the current shell, adds a key to it and runs two git commands:

    #!/bin/bash
    eval &quot;$(ssh-agent -s)&quot;
    ssh-add /home/duvdevan/.ssh/id_rsa
    
    git -C /var/www/duvdevan/ reset --hard origin/master
    git -C /var/www/duvdevan/ pull origin master

Script actually works fine, but every time I run it I get a new process so I think it might become a performance issue and I might end up having useless processes out there.

An example of the output:

    Agent pid 12109
    Identity added: /home/duvdevan/.ssh/custom_rsa (rsa w/o comment)

Also, along with all this, is it possible to find an existing `ssh-agent` process and add my keys into it?

How to check if ssh-agent is already running in bash?

I need to create a shell script wherein I will unzip a password protected zip file. I know the password, and need to automate the unzip process.

How can I achieve this using Unix shell scripting?

unzip password protected zip in unix

Default shell in my mac was bash.  
I have tried to change it into ZSH by command `chsh -s /bin/zsh`.

Now when I am trying to check the shell type, I am getting different responses.

### COMMAND-1
 input : `echo $SHELL`  
output : `/bin/zsh`

### COMMAND-2
input : `ps $o`  
output : `7655 ttys002    0:00.03 -bash`


### COMMAND-3
input : `ps -p $$ | awk &#39;$1 == PP {print $4}&#39; PP=$$`  
output : `-bash`


I am not sure which shell I am using.
Do I need to do something additional to change my shell into **ZSH**.


Which shell I am using in mac

I am trying to install `Docker CE` on `RHEL` using this [link][1]. This is my RHEL version:

    Red Hat Enterprise Linux Server release 7.3 (Maipo)

When I execute this:

    sudo yum -y install docker-ce

I am getting this error:

    Error: Package: docker-ce-17.06.0.ce-1.el7.centos.x86_64 (docker-ce-stable)
               Requires: container-selinux &gt;= 2.9
     You could try using --skip-broken to work around the problem
     You could try running: rpm -Va --nofiles --nodigest

I tried using `--skip-broken` and `rpm -Va --nofiles --nodigest` but again getting the same error. Please let me know how to resolve this issue and install Docker CE in RHEL 7.3.

  [1]: https://stackoverflow.com/questions/42981114/install-docker-ce-17-03-on-rhel7


Docker CE on RHEL - Requires: container-selinux &gt;= 2.9

I have a terminal connected to an external machine through ssh and have a process running in it. 
Is it possible move the execution to the background, so that I can close the ssh connection without the need to kill it? If so how?



Content Type	Original Author	Original Content on Stackoverflow
Question	Anirudh	View Question on Stackoverflow
Solution 1 - Linux	Ouroborus	View Answer on Stackoverflow

DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )" How does that work?

Linux Problem Overview

Linux Solutions

Solution 1 - Linux

What is the trade off between history push and replace?

How do I install ruby gems on Mac

Attributions