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Aliases in Shell Script

              A Bash alias is essentially nothing more than a keyboard shortcut, an abbreviation, a means of avoiding typing a long command sequence. If, for example, we include alias lm="ls -l | more" in the ~/.bashrc file, then each lm typed at the command line will automatically be replaced by a ls -l | more. This can save a great deal of typing at the command line and avoid having to remember complex combinations of commands and options. Setting alias rm="rm -i" (interactive mode delete) may save a good deal of grief, since it can prevent inadvertently losing important files.

Functions in Shell Scripting

Like "real" programming languages, Bash has functions, though in a somewhat limited implementation. A function is a subroutine, a code block that implements a set of operations, a "black box" that performs a specified task. Wherever there is repetitive code, when a task repeats with only slight variations in procedure, then consider using a function.

Process Substitution

                       Piping the stdout of a command into the stdin of another is a powerful technique. But, what if you need to pipe the stdout of multiple commands? This is where process substitution comes in.

Process substitution feeds the output of a process (or processes) into the stdin of another process.

Restricted Shells

Disabled commands in restricted shells

Subshells in Shell Scripting

                      Running a shell script launches a new process, a subshell.