I/O Redirection

There are always three default "files" open, stdin (the keyboard), stdout (the screen), and stderr (error messages output to the screen). These, and any other open files, can be redirected. Redirection simply means capturing output from a file, command, program, script, or even code block within a script  and sending it as input to another file, command, program, or script.

Here Documents

              A here document is a special-purpose code block. It uses a form of I/O redirection to feed a command list to an interactive program or a command, such as ftp, cat, or the ex text editor.

Regular Expressions in Shell Scripting

            To fully utilize the power of shell scripting, you need to master Regular Expressions. Certain commands and utilities commonly used in scripts, such as grep, expr, sed and awk, interpret and use REs. As of version 3, Bash has acquired its own RE-match operator: =~.

Miscellaneous Commands

                Some of the Miscellaneous Commands for linux users

Math Commands in Linux

                   Math Commands in Linux for Reference of LInux users