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How to check if a variable is set in Bash?
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(Usually) The right way
if [ -z ${var+x} ]; then echo "var is unset"; else echo "var is set to '$var'"; fi
where ${var+x} is a parameter expansion which evaluates to nothing if var is unset, and substitutes the string x otherw...
Vim users, where do you rest your right hand? [closed]
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I think that jkl; is actually the more appropriate usage for vi. For one, h and l really don't matter that much. w, e, and b are significantly more useful for horizontal navigation. As a bonus, ; is easy to get at if the language requires it. Having ...
MPICH vs OpenMPI
...xtensive optimizations that make it the preferred implementation in nearly all cases.
Feature Support from the Latest MPI Standard
An orthogonal axis to hardware/platform support is coverage of the MPI standard. Here MPICH is usually far and away superior. MPICH has been the first implementation...
Downcasting in Java
Upcasting is allowed in Java, however downcasting gives a compile error.
11 Answers
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How to change past commit to include a missed file?
...s that the case even if I am the only user of the remote repo? Wouldn't it allow me to do git push -f if I am sure the upstream didn't change?
– kolrie
Jan 16 '13 at 22:48
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Android screen size HDPI, LDPI, MDPI [duplicate]
I have a background that I need fit in all screen sizes. I have three folders, hdpi , ldpi and mdpi for drawables, but in the emulator there isn't any referense to what resolution hdpi is and what mdpi and ldpi are.
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How to avoid overflow in expr. A * B - C * D
...e their types are: signed long long int A, B, C, D;
Each number can be really big (not overflowing its type). While A*B could cause overflow, at same time expression A*B - C*D can be really small. How can I compute it correctly?
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Why do I need to override the equals and hashCode methods in Java?
...hich will prevent your class from functioning properly in conjunction with all hash-based collections, including HashMap, HashSet, and Hashtable.
Let's try to understand it with an example of what would happen if we override equals() without overriding hashCode() and attempt to use a Map.
Say we ha...
MongoDB: How to query for records where field is null or not set?
...ount({sent_at: {$exists: false}})
If its there and null, or not there at all:
db.emails.count({sent_at: null})
Refer here for querying and null
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Create a dictionary with list comprehension
...(key)) for key in keys)
In simple cases you don't need a comprehension at all...
But if you already have iterable(s) of keys and/or values, just call the dict built-in directly:
1) consumed from any iterable yielding pairs of keys/vals
dict(pairs)
2) "zip'ped" from two separate iterables of keys/v...