Here is a list of articles that should be saved for further reference.
2: Linux VARIABLES:
$$ = The PID number of the process executing the shell.
$? = Exit status variable.
$0 = The name of the command you used to call a program.
$1 = The first argument on the command line.
$2 = The second argument on the command line.
$n = The nth argument on the command line.
$* = All the arguments on the command line.
$# The number of command line arguments.
3: Setting default editor in bash shell.
6: Filesystem definition.
In computing, a file system (often also written as filesystem) is a method of storing and organizing computer files and the data they contain to make it easy to find and access them.
10: Replace a word or a pattern with another word or pattern in all files in a directory. Lets say we have 5 files in a directory and almost all files have a word “PRESENT-SYNTAX” and you want to replace it with “NEWSYNTAX” then we use following command. Make sure to get into the corresponding directory before running the command.
sed -i “s/PRESENT-SYNTAX/NEWSYNTAX/g” *
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