This is called &quot;Parameter Expansion&quot; available in bash version 4+ . To change the case of the string stored in the variable to lower case.Eg: 

    var=HeyThere
    echo ${var,,}
    heythere

You may want to try some additional commands and check the effect : [source][1]

    ${var^}
    ${var^^}
    ${var,}
    ${var,,}




Note: &quot;Parameter Expansion&quot; is present in `man bash` .Search for it. 
  [1]: http://wiki.bash-hackers.org/syntax/pe




The introductory documentation, which I am reading ([TOC here][1]) uses the term &quot;batch&quot; ([for instance here][2]) without having defined it.



[1]: https://www.tensorflow.org/get_started/
[2]: https://www.tensorflow.org/tutorials/keras/classification

What is a batch in TensorFlow?

I was reading the es6 import statement [reference on MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import). The syntax:

    import &quot;my-module&quot;;

will import an entire module for side effects only, without importing any bindings. I am not sure what **side effects** mean. I have been using with **angular** by saying `import &quot;angular&quot;`. Angular binds to window but does not return a object. So I am not sure if this would be called as a side effect exactly.

 

es6 import for side effects meaning

Recently I came across this syntax:

    ${reportName,,}

I could not find anything by googling, so does anyone know what does those ,, mean?

What does 2 commas after variable name mean in bash?

Recently I came across this syntax:
<pre><code class="hljs language-bash">${reportName,,}
</code></pre>
I could not find anything by googling, so does anyone know what does those ,, mean?

I&#39;m trying to install [Prestissimo][1] to an Ubuntu 16.04 server, but that leads to an error:

    $ composer global require &quot;hirak/prestissimo:^0.3&quot;
    Changed current directory to /home/kramer65/.composer
    
    
      [ErrorException]
      file_put_contents(./composer.json): failed to open stream: Permission denied
    
    
    require [--dev] [--prefer-source] [--prefer-dist] [--no-progress] [--no-update] [--no-scripts] [--update-no-dev] [--update-with-dependencies] [--ignore-platform-reqs] [--prefer-stable] [--prefer-lowest] [--sort-packages] [-o|--optimize-autoloader] [-a|--classmap-authoritative] [--] [&lt;packages&gt;]...

I&#39;m logged in as user `kramer65`, so I wouldn&#39;t know why it can&#39;t write to my home folder. My normal reaction to a `permission denied` is to use `sudo`, but composer then always says:

&gt; Do not run Composer as root/super user! See https://getcomposer.org/root for details

Any idea how I can solve this?

  [1]: https://github.com/hirak/prestissimo

Composer: file_put_contents(./composer.json): failed to open stream: Permission denied

I realize this question has already been asked in some different ways, however it doesn&#39;t seem like any of the ways I&#39;ve come across have worked to fix this problem, so here it goes:

I&#39;m trying to connect to my raspberry pi 3 raspbian setup via ssh on my laptop, but although I have the correct ip address, I keep getting the error: 
        
    ssh: connect to host xxx.xxx.xx.x port 22: connection refused.

This is unusual because when I try to ping that address, it works fine. Is there anything I can try to figure out what&#39;s wrong? 

Also keep in mind I am relatively inexperienced with bash in linux, so inclusion of any specific commands with a description of what they do would be greatly appreciated.

ssh connection refused on Raspberry Pi

I&#39;m trying to compile Python 3.6 on an arm based Linux machine, 
`./configure` outputs this:

&gt; If you want a release build with all optimizations active (LTO, PGO, etc),
please run `./configure --enable-optimizations`.

what does `--enable-optimizations` do?


what does --enable-optimizations do while compiling python?

I am trying to install fuzzywuzzy onto my Anaconda distribution in 64 bit Linux. When I do this, it tries to change my `conda`, and `conda-env` to `conda-forge` channels. As follows:

I search anaconda for fuzzy wuzzy by writing:

    anaconda search -t fuzzywuzzy

This showed that the most up to date version available for anaconda on 64 bit Linux is 0.13 provided on the channel `conda-forge`.

To install, within the command line, I type:

    conda install -c conda-forge fuzzywuzzy=0.13.0


I get the following output:

    The following packages will be downloaded:
    
    package                    |            build
    ---------------------------|-----------------
    conda-env-2.6.0            |                0         1017 B  conda-forge
    python-levenshtein-0.12.0  |           py27_0         138 KB  conda-forge
    conda-4.2.13               |           py27_0         375 KB  conda-forge
    fuzzywuzzy-0.11.0          |           py27_0          15 KB  conda-forge
    ------------------------------------------------------------
                                       Total:         528 KB


    The following new packages will be INSTALLED:

        fuzzywuzzy:            0.11.0-py27_0 conda-forge
        python-levenshtein:    0.12.0-py27_0 conda-forge

    The following packages will be SUPERCEDED by a higher-priority channel:

        conda:        4.2.13-py27_0      --&gt; 4.2.13-py27_0 conda-forge 
        conda-env:    2.6.0-0            --&gt; 2.6.0-0       conda-forge 

    Proceed ([y]/n)?

I do not understand what this is telling me.

What does this mean? Am I right in thinking that this is changing my default package manager channels? Can this be reversed if I go ahead and install it? Is there any way to complete the installation without changing the default channel? Or is favouring the superceding channels something that I should be doing? 

I don&#39;t want to change my distribution just for one module, or cause further headaches.

This question: https://github.com/conda/conda/issues/2898 sounds like its telling me that I should just let it happen. What do?

(I am using anaconda version: 4.2.13 and Python 2.7.12)

What does &quot;the following packages will be superseded by a higher priority channel&quot; mean?

I am working on a Java project with gradlew. I use Ubuntu Linux as my OS. When I run &quot;gradle&quot; it runs, and gives me info. But when I run &quot;gradlew&quot;, it outputs as &quot;No command &#39;gradlew&#39; found, did you mean:
 Command &#39;gradle&#39; from package &#39;gradle&#39; (universe)
gradlew: command not found&quot;

I did my research, I have jdk, and I did sudo apt-get install gradle. I am totally clueless


Error is:
```
$ gradlew clean jpackage
bash: gradlew: command not found...
```

gradlew command not found?

I have bash installed on my W10 laptop, but one thing that is very frustrating is I can not scroll up. 

Does anyone know of a way to enable scrolling with the mouse wheel? I could not find anything after many google searches.

Context: If I compile some C++ files and get a lot of errors, I can not scroll up to see all those errors.

Windows 10 Bash (Ubuntu) - How to scroll up?

What is the shortcut to search my command history in macOS terminal? 

For how long is the history available for searching? Where is it stored?


Searching your command history on macOS terminal

I&#39;d like to know if it&#39;s possible to check if there are certain files in a certain bucket.

This is what I&#39;ve found:

https://stackoverflow.com/questions/17455782/checking-if-a-file-is-in-a-s3-bucket-using-the-s3cmd

&gt; It should fix my problem, but for some reason it keeps returning that the file doesn&#39;t exist, while it does. This solution is also a little dated and doesn&#39;t use the `doesObjectExist` method.

[Summary of all the methods that can be used in the Amazon S3 web service][1]

&gt; This gives the syntax of how to use this method, but I can&#39;t seem to make it work.

Do they expect you to make a boolean variable to save the status of the method, **or** does the function directly give you an output / throw an error?

This is the code I&#39;m currently using in my bash script:

    existBool=doesObjectExist(${BucketName}, backup_${DomainName}_${CurrentDate}.zip)
    
    if $existBool ; then
            echo &#39;No worries, the file exists.&#39;
    fi

I tested it using only the name of the file, instead of giving the full path. But since the error I&#39;m getting is a syntax error, I&#39;m probably just using it wrong.

Hopefully someone can help me out and tell me what I&#39;m doing wrong.

**!Edit**

I ended up looking for another way to do this since using `doesObjectExist` isn&#39;t the fastest or easiest.

  [1]: http://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/com/amazonaws/services/s3/AmazonS3.html#doesObjectExist-java.lang.String-java.lang.String-


AWS S3: How to check if a file exists in a bucket using bash

I get `Cannot iterate over null (null)` from the below query because `.property_history` is not present in `result` object.

How do i check for the presence of `.property_history` key before proceeding with `map(...)` ?

I tried using something like ``sold_year= `echo &quot;$content&quot; | jq &#39;if has(&quot;property_history&quot;) then 
map(select(.event_name == &quot;Sold&quot;))[0].date&#39; else null end``

**Original Query:**

    sold_year=`echo &quot;$content&quot; | jq &#39;.result.property_history | map(select(.event_name == &quot;Sold&quot;))[0].date&#39;`

**JSON:**

    {  
       &quot;result&quot;:{  
          &quot;property_history&quot;:[  
             {  
                &quot;date&quot;:&quot;01/27/2016&quot;,
                &quot;price_changed&quot;:0,
                &quot;price&quot;:899750,
                &quot;event_name&quot;:&quot;Listed&quot;,
                &quot;sqft&quot;:0
             },
             {  
                &quot;date&quot;:&quot;12/15/2015&quot;,
                &quot;price_changed&quot;:0,
                &quot;price&quot;:899750,
                &quot;event_name&quot;:&quot;Listed&quot;,
                &quot;sqft&quot;:2357
             },
             {  
                &quot;date&quot;:&quot;08/30/2004&quot;,
                &quot;price_changed&quot;:0,
                &quot;price&quot;:739000,
                &quot;event_name&quot;:&quot;Sold&quot;,
                &quot;sqft&quot;:2357
             }
          ]
       }
    }



How to check for presence of &#39;key&#39; in jq before iterating over the values

I want to setup some configuration when my container starts, for this I am using shell scripts. But my container will exits as soon as my scripts ends, I have tried with -d flag / detached mode but It will never run in detached mode.

Below is my Dockerfile

    FROM ubuntu:14.04

    ADD shell.sh /usr/local/bin/shell.sh

    RUN chmod 777 /usr/local/bin/shell.sh

    CMD /usr/local/bin/shell.sh

Below is my shell script

    #!/bin/bash
    echo Hello-docker

1. Run without any flag

        docker run hello-docker
This will print &#39;Hello-docker&#39; on my console and exits
2. Run with -itd flags

        docker run -itd hello-docker
and as below my console output, This time also will exits soon.  **:(**
[![enter image description here][1]][1]

 - The difference I saw is in COMMAND section when I run other images command section will shows &quot;/bin/bash&quot; and will continue in detached mode.

 - And when I run my image in container with shell script COMMAND section will show &quot;/bin/sh -c /usr/loca&quot;, and Exit.

 - I want to run container till I not stop it manually.

EDIT:

After adding ENTRYPOINT instruction in Dockerfile, this will not execute my shell script :(

    FROM ubuntu:14.04

    ADD shell.sh /usr/local/bin/shell.sh

    RUN chmod 777 /usr/local/bin/shell.sh

    CMD /usr/local/bin/shell.sh
    
    ENTRYPOINT /bin/bash
As per docker documentation [here][2]

CMD will be overridden when running the container with alternative arguments, so If I run docker image with some arguments as below, will not execute CMD instructions. :(

    sudo docker run -it --entrypoint=/bin/bash &lt;imagename&gt;
  [1]: https://i.stack.imgur.com/gXaRd.png
  [2]: https://docs.docker.com/engine/reference/builder/#understand-how-cmd-and-entrypoint-interact

Dockerfile CMD instruction will exit the container just after running it

Here&#39;s my docker-compose:

    version: &#39;2&#39;
    services:
      couchpotato:
        build:
            context: ./couchpotato
            dockerfile: Dockerfile
        ports:
         - 5050:5050
        volumes:
         - &quot;${PWD}/couchpotato/data:/home/CouchPotato/data/&quot;
         - &quot;${PWD}/couchpotato/config:/home/CouchPotato/config/&quot;

When I run it inside the shell, in the directory of the docker-compose.yml, I get:

    WARNING: The PWD variable is not set. Defaulting to a blank string.
and the compose starts with PWD being empty. 

I don&#39;t see any error in the file, as seen here: https://docs.docker.com/compose/environment-variables/

Docker compose won&#39;t find $PWD environment variable

As mentioned above, I need to install only the mongo shell on a RHEL instance (machine A).
I have a mongodb server on a separate instance (machine B) and need to connect to that from A to run `mongodump` and `mongorestore` commands.

I tried looking it up on the web but all I got was instructions to install the complete mongodb package.

Any help appreciated.

Install ONLY mongo shell, not mongodb

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

I&#39;m struggling to see why the following is returning a code of 1.

    echo &#39;Total&#39; | grep -c No
    0

So &quot;No&quot; doesn&#39;t exists in &quot;Total&quot;. But then looking up its return code I&#39;m seeing it as 1.

    echo $?
    1

Why is return code showing up as 1? Is there a way to get around this?




Content Type	Original Author	Original Content on Stackoverflow
Question	user1308345	View Question on Stackoverflow
Solution 1 - Linux	P....	View Answer on Stackoverflow

What does 2 commas after variable name mean in bash?

Linux Problem Overview

Linux Solutions

Solution 1 - Linux

es6 import for side effects meaning

What is a batch in TensorFlow?

Attributions