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What is the best way to ensure only one instance of a Bash script is running? [duplicate]
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If the script is the same across all users, you can use a lockfile approach. If you acquire the lock, proceed else show a message and exit.
As an example:
[Terminal #1] $ lockfile -r 0 /tmp/the.lock
[Terminal #1] $
[Terminal #2] $ lockfile -r 0 /tmp/the....
Run a callback only if an attribute has changed in Rails
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Rails 5.1+
class Page < ActiveRecord::Base
before_save :do_something, if: :will_save_change_to_status_id?
private
def do_something
# ...
end
end
The commit that changed ActiveRecord::Dirty is here: https://github.com/rails/rails/commit/16ae3db5a5c6a08383b974ae...
How do you know when to use fold-left and when to use fold-right?
...ee it. It's "haskell-style pseudocode". :)
– laughing_man
Apr 21 '15 at 2:38
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Why use HttpClient for Synchronous Connection
I am building a class library to interact with an API. I need to call the API and process the XML response. I can see the benefits of using HttpClient for Asynchronous connectivity, but what I am doing is purely synchronous, so I cannot see any significant benefit over using HttpWebRequest .
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Max size of an iOS application
...whose MinimumOSVersion is less than 7.0: maximum of 80 MB for the total of all __TEXT sections in the binary.
For apps whose MinimumOSVersion is 7.x through 8.x: maximum of 60 MB per slice for the __TEXT section of each architecture slice in the binary.
For apps whose MinimumOSVersion is 9.0 or grea...
SQLAlchemy: how to filter date field?
...In fact, your query is right except for the typo: your filter is excluding all records: you should change the <= for >= and vice versa:
qry = DBSession.query(User).filter(
and_(User.birthday <= '1988-01-17', User.birthday >= '1985-01-17'))
# or same:
qry = DBSession.query(User)....
MongoDB not equal to
...b.inventory.find( { price: { $not: { $gt: 1.99 } } } )
That would select all documents where:
The price field value is less than or equal to 1.99 or the price
Field does not exist
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How can I extract the folder path from file path in Python?
....path.split(os.path.abspath(existGDBPath))
('T:\\Data\\DBDesign', 'DBDesign_93_v141b.mdb')
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javac is not recognized as an internal or external command, operable program or batch file [closed]
...nal or external command... error message.
In a nutshell, you have not installed Java correctly. Finalizing the installation of Java on Windows requires some manual steps. You must always perform these steps after installing Java, including after upgrading the JDK.
Environment variables and PATH
(...
MFC 获取当前时间的几种方法总结 - C/C++ - 清泛网 - 专注C/C++及内核技术
...ime curTime = CTime::GetCurrentTime();CString strCurTime;strCurTime.Format(_T("d d d d:d:d"), curTime...1.CTime类获取当前时间
CTime curTime = CTime::GetCurrentTime();
CString strCurTime;
strCurTime.Format(_T("d/d/d d:d:d"), curTime.GetYear(), curTime.GetMonth(), curTime.GetDay(), curTi...