Terminal Commands

• touch
  • command used to create a file in the current working directory if it does not exist and if it does exist - it changes the timestamp of the same
  • example: touch index.html

Shell Scripting

• echo
  • used to send out to message to the standard output that is terminal
  • example: echo hello_world
  • echo command can also be used to create a file
  • example: echo > index.html
• file execution
  • if the files are to be executed from their default execution then bash command should be prefixed.
  • example, to execute the hello.sh file in its default permissions mode we need to run bash hello.sh.
  • if you need to perform standalone execution then change the permission by running chmod 755 hello.sh
    • now you can execute the file just by ./hello.sh
• the interpreter line / shebang
  • each shell script file should start with the interpreter line or what is famously known as shebang
    • the reason for this being - the terminal should know what shell to execute the script in
    • example - #!/usr/bin/env bash
• variable
  • the value of a variable can be accessed using the $ symbol. See, greeting.sh for example
  • as a best practice, it is good to have variable names in uppercase.
• Branching and Looping
  • if statement
    • Refer here
  • else statement
    • Refer here
  • elif statement
    • Refer here
  • while loop
    • Refer here
  • for loop
    • Refer here
  • break / continue loop
    • Refer here
  • Environment Variables
    • These are the system defined variables which hold soem system value
    • Example: $PATH, $TERM, $MONITOR
  • Functions:
    • a function is a logical grouping of objects
    • Functions can take in parameters which can be assigned to global variable or local variable
    • See here for a sample functions program.
  • Pipes:
    • A command line technique in which multiple commands can be piped together to form a single interdependent command and execute in a silo.
    • An example of piped shell script can be found here