How to check if environment variable is set using shell script?

If you are wondering how can we check whether an environment variable is set or not in the system, here are few methods :

1. Manually

a. Run “set” command on the shell prompt, it will list out all the variables set in the system :

# set

b. Run “echo” command on the shell to print the value of the environment variable :

# echo $<environment variable>

2. Through Shell Script

Let say we intent to check whether environment variable “envVar” is set or not?

a. Method 1 – checking if “envVar” is set to “” (no value) :

if [ "$envVar" == "" ]

then

echo “envVar is not set”

else

echo “envVar is set”

b.Method 2 – checking if “envVar” is non NULL :

if [ -n "$envVar" ]

then

echo “envVar has non NULL value, it is set.”

else

echo “envVar has NULL value, it is not set.”

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Exploring Node.js Internals

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While running a code after building it using glibc, if you get this error : glibc detected : double free or corruption (fasttop) To fix this error export " MALLOC_CHECK_" environment variable : export MALLOC_CHECK_=0 Then, try running the program. It worked in my case.

Hibernate Object Conversations

Session methods to use for object conversations Save() A new instance being attached to the session. An insert will be scheduled. Update() Call Update to make a transient object persistent again. It will force a SQL update on the transient object. This is because Hibernate does not know whether the object is dirty or not and to be safe by default schedules an update. This method will throw an exception, if the entity is already registered with the session. - NonUniqueObjectException is thrown. saveOrUpdate() Either a save or an update will be called based on whether the identifier exists or not. No identifier - save is called, else update is called. Or for a better understanding, if the object is transient, then a save is called, if the object is persistent, then an update is called. Reattaching an unmodified instance - If you know for sure that an object is not modified and you just want to make it persistent again - Session.lock(item, LockMode.No

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