UNIX : What is /dev/null ?

/dev/null is a file where you can discard the output of the command executed.
This file is also called as Bit Bucket.

eg :

>ls -ltr > /dev/null
>

Here the output of command ls is never shown on terminal STDOUT. It is redirected to bit bucket.

Sometimes we need not display the output as well as error message of command.In this case use the following command.

> command > /dev/null 2>&1

The command output is redirected to /dev/null.Also the error output, STDERR (which is called by 2) is redirected to STDOUT (called as 1 ).That means the error will be redirected to /dev/null.

Comments

UNIX : How to ignore lines with certain names

Sometimes we need to ignore multiple lines with certain words and get the list out of the file. usually it will be a log file to read . The below grep command can be used to ignore multiple words present in a text file. Lets say the file contain $ cat list.txt apple orange apple banana papaya Now we need to ignore line with orange , banana and papaya . So we can use the below grep command. $ cat list.txt | grep -Ev "orange|banana|papaya" apple apple It will ignore lines with the words in -v part of grep.

UNIX : How to get record count from zipped file

Sometimes we may need to get records count from file . For that we can use wc -l , command with file name. In some situation the file will be in compressed format . wc -l will not directly work with zipped files . In this case we can do zcat the file and pipe the word count command with it. Example : Let say we have a file cricketData.dat.gz To get word count from the file use : zcat cricketData.dat.gz | wc -l This will give the record count.

Scala

Scala is a object oriented functional type programing language. All variables declared in scala is considered as objects.

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