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Interpreted Programming Languages:
The shell

Interpreted Language (Shells, Perl, Python, WYSIWYG document editors):

• Interpreter
• Script

Shells:

• programs that offer basic command line features
• started at login (and not only)
• handle environment variables 
• start all the other processes
• Examples:
• sh, bash
• csh, tcsh

Bash

Configuration:

• global: /etc/profile, /etc/bashrc, /etc/profile.d/*.sh
• user defined: ~/.bash_profile, ~/.bashrc

Environment variables:

• defined: at login time, when a new shell starts
• inheritance: export 
• display: env, echo $NAME

Programming language features:

• variables: strings, number value by context
• assignment: NAME="aaa"
• evaluation: $NAME, ${NAME}, "  ", '  ', `  `
• separators: spaces, tabs, newlines, $IFS, ;, #
• input/output: $0, $1, ..., export, echo, >, >>, <, >&, exit
• operations:
• arithmetic ->  let NAME=$NAME+1
• string ->  NAME=$NAME+1, set - $NAME
• flow control:
• [ test ] -> [ -f /etc/profile ], [ "$NAME" = "1+1" ]
• if [ test ] ; then ... ; fi
• while [ test ] ; do ... ; done
• for NAME in $LIST ; do ... ; done