In `bash`&lt;sup&gt;(1)&lt;/sup&gt;, `read` has a `-t` option where you can specify a timeout. From the manpage:

&gt; `read [-ers] [-u fd] [-t timeout] [-a aname] [-p prompt] [-n nchars] [-d delim] [name ...]`
&gt;
&gt; `-t timeout: ` cause read to time out and return failure if a complete line of input is not read within timeout seconds.  This option has no effect  if read is not reading input from the terminal or a pipe.

Transcript below (without hitting ENTER):

    $ date ; read -t 10 -p &quot;Hit ENTER or wait ten seconds&quot; ; echo ; date
    Tue Feb 28 22:29:15 WAST 2012
    Hit ENTER or wait ten seconds
    Tue Feb 28 22:29:25 WAST 2012

Another, hitting ENTER after a couple of seconds:

    $ date ; read -t 10 -p &quot;Hit ENTER or wait ten seconds&quot; ; date
    Tue Feb 28 22:30:17 WAST 2012
    Hit ENTER or wait ten seconds
    Tue Feb 28 22:30:19 WAST 2012

And another, hitting CTRL-C:

    $ date ; read -t 10 -p &quot;Hit ENTER or wait ten seconds&quot; ; echo ; date
    Tue Feb 28 22:30:29 WAST 2012
    Hit ENTER or wait ten seconds

---

&lt;sup&gt;(1)&lt;/sup&gt; If you&#39;re doing this in a script, make ***sure*** that it&#39;s a `bash` one. You can do that by adding a shebang line at the start such as one of the following:

```none
#!/usr/bin/env bash
#!/bin/bash
```


The `read` builtin has a timeout.

    read -t 10

will do it

Building on the thoughtful answers above, the return value from the read is useful to distinguish between an empty  response from the user (for example &quot;Press Enter&quot; for the default action) and a timeout.

    read -t 5 -p &quot;Prompt &quot; RESP
    if [[ $? -gt 128 ]] ; then
        echo -e &quot;\nTimeout&quot;
    else
        echo &quot;Response = \&quot;$RESP\&quot;&quot;  # adding quotes so empty strings are obvious
    fi

Another useful tidbit is that the `-p &quot;prompt &quot;` is written to stderr (not stdout) so if you&#39;re redirecting stderr, the prompt will not be displayed. An example of this would be logging an execution trace to a log file for later analysis. To use `read -p Prompt` in this case you can redirect stderr to the user for just the read statement.

    set -x
    exec 2&gt;logfile
    read -t 5 -p &quot;Prompt &quot; RESP 2&gt;/dev/tty
 

From the [bash reference manual](http://www.gnu.org/software/bash/manual/bashref.html) :

 &gt; `read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] `*`[-t timeout]`*` [-u fd] [name ...]`

I have two lists

    first = list(a = 1, b = 2, c = 3)
    second = list(a = 2, b = 3, c = 4)

I want to merge these two lists so the final product is 

    $a
    [1] 1 2
    
    $b
    [1] 2 3
    
    $c
    [1] 3 4

Is there a simple function to do this? 

Merge Two Lists in R

I&#39;m using rails 3.2 and devise 2.0 and I&#39;m quite new to Rails.

# Requirements #

I&#39;d like to achieve the following:

 - have 2 or more &quot;user&quot; models, eg. Member, Customer, Admin
 - all models share some required fields (eg. email and password)
 - each model may have some unique fields (eg. company for Customer only)
 - some fields may be shared but not have the same validation (eg. name is required for Customer but optional for Member)
 - all fields must be filled during the registration process, so the forms are different
 - the login form should be unique

# Possible solutions #

I googled and searched StackOverflow for quite a long time, but nothing seems right to me (I&#39;m a Java guy, sorry :) and now I&#39;m quite confused. Two solutions came up:

## Single devise user ##

That&#39;s the most frequent answer. Just create the default devise User and create relations between Member--&gt;User and Customer--&gt;User.
My concern here is how can I achieve a customized registration process for each model? I tried different things but all ended as a mess!

## Multiple devise users ##

This solves the custom registration process, and seems right to me, but the unique login form is a blocker. I found an answer on SO (&lt;https://stackoverflow.com/questions/7254734/devise-login-from-two-model&gt;) which suggests to override Devise::Models::Authenticatable.find_for_authentication(conditions).
That seems complicated (?) and since I&#39;m new to rails, I&#39;d like to know if that could work?

Thanks for your advice!

devise and multiple &quot;user&quot; models

I can ask the user to press &lt;kbd&gt;Enter&lt;/kbd&gt; by using `read`, and have him wait by calling `sleep`. But I&#160;can’t think of a way of doing both at the same time. I&#160;would like the user to be given the choice:

*Press &lt;kbd&gt;Ctrl&lt;/kbd&gt;+&lt;kbd&gt;C&lt;/kbd&gt; to Cancel, &lt;kbd&gt;Enter&lt;/kbd&gt;&#160;to continue or just wait 10&#160;seconds*

How can I&#160;do that?

How to use Bash read with a timeout?

I can ask the user to press <kbd>Enter</kbd> by using <code>read</code>, and have him wait by calling <code>sleep</code>. But I can’t think of a way of doing both at the same time. I would like the user to be given the choice:
Press <kbd>Ctrl</kbd>+<kbd>C</kbd> to Cancel, <kbd>Enter</kbd> to continue or just wait 10 seconds
How can I do that?

I know how to write a multi-line command in a Bash script, but how can I add a comment for each line in a multiline command?

    CommandName InputFiles      \ # This is the comment for the 1st line
                --option1 arg1  \ # This is the comment for the 2nd line
                --option2 arg2    # This is the comment for the 3nd line

But unfortunately, the comment after continuation character `\` will break the command.



How to put a line comment for a multi-line command

    foo=&quot;/sdf/here/jfds&quot;
    bar=&quot;${foo##*/}&quot;

Can anyone explain how the &quot;`${foo##*/}`&quot; expression works? I understand it will return the string after the last forward slash (i.e. jfds). However, I have no idea how it does or what this type of expression is called?

Expression after last specific character

So far I&#39;ve been able to find out how to add a line at the beginning of a file but that&#39;s not exactly what I want. I&#39;ll show it with an example:

**File content**

    some text at the beginning

**Result**

    &lt;added text&gt; some text at the beginning

It&#39;s similar but I don&#39;t want to create any new line with it...

I would like to do this with `sed` if possible.


How to insert a text at the beginning of a file?

I would like to get only the value of a MySQL query result in a bash script. For example the running the following command:

    mysql -uroot -ppwd -e &quot;SELECT id FROM nagios.host WHERE name=&#39;$host&#39;&quot;

returns:

    +----+
    | id |
    +----+
    | 0  |
    +----+
How can I fetch the value returned in my bash script?

How to fetch field from MySQL query result in bash

I&#39;m looking for the best way to duplicate the Linux &#39;watch&#39; command on Mac&amp;nbsp;OS&amp;nbsp;X. I&#39;d like to run a command every few seconds to pattern match on the contents of an output file using &#39;tail&#39; and &#39;sed&#39;.

What&#39;s my best option on a Mac, and can it be done without downloading software?






OS X Bash, &#39;watch&#39; command

I need to do it for more predictable benchmarking.

How to purge disk I/O caches on Linux?

In *scatter* and *gather* (i.e. `readv` and `writev`), Linux reads into multiple buffers and writes from multiple buffers.

If say, I have a vector of 3 buffers, I can use `readv`, OR I can use a single buffer, which is of combined size of 3 buffers and do `fread`.

Hence, I am confused: For which cases should scatter/gather be used and when should a single large buffer be used?

Linux: When to use scatter/gather IO (readv, writev) vs a large buffer with fread

I&#39;m getting `IOError: [Errno 13] Permission denied` and I don&#39;t know what is wrong wit this code.

I&#39;m trying to read a file given an absolute path (meaning only `file.asm`),

and a relative path (meaning `/.../file.asm`), and I want the program to write the file to whatever path is given - if it is absolute, it should write it to the current dir; otherwise, to the path given.

the code:

    #call to main function
    if __name__ == &#39;__main__&#39;:
	    assem(sys.argv[1])


    import sys
    
    def assem(myFile):
	    from myParser import Parser
	    import code
	    from symbolTable import SymbolTable
	
	    table=SymbolTable()
	
	    # max size of each word
	    WORD_SIZE = 16
	    # rom address to save to
	    rom_addrs = 0
	    # variable address to save to
	    var_addrs = 16
	
	    # new addition
	    if (myFile[-4:] == &quot;.asm&quot;):
	        newFile = myFile[:4]+&quot;.hack&quot;

        output = open(newFile, &#39;w&#39;) &lt;==== ERROR

the error given:

    IOError: [Errno 13] Permission denied: &#39;/Use.hack&#39;

the way I execute the code : 

    python assembler.py Users/***/Desktop/University/Add.asm 



What am I doing wrong here?


Python - IOError: [Errno 13] Permission denied:

When a file is created (`FileSystemWatcher_Created`) in one directory I copy it to another. But When I create a big (&gt;10MB) file it fails to copy the file, because it starts copying already, when the file is not yet finished creating...  
This causes **Cannot copy the file, because it&#39;s used by another process** to be raised. ;(  
Any help?


    class Program
    {
        static void Main(string[] args)
        {
            string path = @&quot;D:\levan\FolderListenerTest\ListenedFolder&quot;;
            FileSystemWatcher listener; 
            listener = new FileSystemWatcher(path);
            listener.Created += new FileSystemEventHandler(listener_Created);
            listener.EnableRaisingEvents = true;
    
            while (Console.ReadLine() != &quot;exit&quot;) ;
        }
    
        public static void listener_Created(object sender, FileSystemEventArgs e)
        {
            Console.WriteLine
                    (
                        &quot;File Created:\n&quot;
                       + &quot;ChangeType: &quot; + e.ChangeType
                       + &quot;\nName: &quot; + e.Name
                       + &quot;\nFullPath: &quot; + e.FullPath
                    );
            File.Copy(e.FullPath, @&quot;D:\levan\FolderListenerTest\CopiedFilesFolder\&quot; + e.Name);
            Console.Read();
        }
    }

Wait Until File Is Completely Written

I was a little confused by this expression:


    gcc -c -g program.c &gt;&amp; compiler.txt

I know `&amp;&gt;filename` will redirect both stdout and stderr to file `filename`.  But in this case the ampersand is after the greater than sign.  It looks like its of the form `M&gt;&amp;N`, where `M` and `N` are file descriptors.

In the snippet above, does `M=1` and `N=&#39;compiler.txt&#39;`?  How exactly is this different from:

    gcc -c -g program.c &gt; compiler.txt     (ampersand removed)

My understanding is that each open file is associated with a file descriptor greater than 2.  Is this correct?

If so, is a file name interchangeable with its file descriptor as the target of redirection?

What does &gt;&amp; mean?

Do PHP sessions timeout by default - ie without any coding on my part would a user eventually be &quot;logged out&quot; after some time of inactivity?



PHP sessions default timeout

Why would this work

    timeout 10s echo &quot;foo bar&quot; # foo bar
but this wouldn&#39;t

    function echoFooBar {
      echo &quot;foo bar&quot;
    }

    echoFooBar # foo bar

    timeout 10s echoFooBar # timeout: failed to run command `echoFooBar&#39;: No such file or directory

and how can I make it work?

Execute a shell function with timeout

In a Bash script, I would like to do something like:

    app1 &amp;
    pidApp1=$!
    app2 &amp;
    pidApp2=$1
    
    timeout 60 wait $pidApp1 $pidApp2
    kill -9 $pidApp1 $pidApp2

I.e., launch two applications in the background, and give them 60 seconds to complete their work. Then, if they don&#39;t finish within that interval, kill them.

Unfortunately, the above does not work, since `timeout` is an executable, while `wait` is a shell command. I tried changing it to:

    timeout 60 bash -c wait $pidApp1 $pidApp2

But this still does not work, since `wait` can only be called on a PID launched within the same shell.

Any ideas?

Bash: wait with timeout

&gt; **Possible Duplicate:**  
&gt; [Bash script that kills a child process after a given timeout](https://stackoverflow.com/questions/5161193/bash-script-that-kills-a-child-process-after-a-given-timeout)  

&lt;!-- End of automatically inserted text --&gt;

Is there a way to write a shell script that would execute a certain command for 15 seconds, then kill the command?

I have tried sleep, wait and ping but maybe I am using them wrong.

How to run a process with a timeout in Bash?

I am calling a series of links using the [`file_get_contents()`](http://php.net/file_get_contents) method in a loop. Each link may take more than 15 minutes to process. Now, I worry about whether PHP&#39;s `file_get_contents()` has a timeout period?

If yes, it will time out with a call and move to next link. I don&#39;t want to call the next link without the prior one finishing.

So, please tell me whether `file_get_contents()` has a timeout period. The file which contains the `file_get_contents()` is set to [`set_time_limit()`](http://php.net/set_time_limit) to zero (unlimited).

Content Type	Original Author	Original Content on Stackoverflow
Question	qdii	View Question on Stackoverflow
Solution 1 - Bash	paxdiablo	View Answer on Stackoverflow
Solution 2 - Bash	Johannes Weiss	View Answer on Stackoverflow
Solution 3 - Bash	user2070305	View Answer on Stackoverflow
Solution 4 - Bash	Benoit	View Answer on Stackoverflow

How to use Bash read with a timeout?

Bash Problem Overview

Bash Solutions

Solution 1 - Bash

Solution 2 - Bash

Solution 3 - Bash

Solution 4 - Bash

devise and multiple "user" models

Merge Two Lists in R

Attributions