BASH TIPS

File Discreptor:

File input and output are accomplished by integer handles that track all open files for a given process. These numeric values are known as file descriptors. The best known file descriptors are stdin, stdout and stderr, with file descriptor numbers 0, 1 and 2, respectively. These numbers and respective devices are reserved.

Redirection:

<: redirect input 
>: redirect output

Before a command is executed, its input and output may be redirected using a special notation interpreted by the shell.

Pipelines(|):

The output of each command in the pipeline is connected via a pipe to the input of the next command.

String Manipulation

see reference

Bath Math

See reference

Use "\" to make a command lay cross several lines in script