Special Parameters

[nixpulvis]

Section 2.5.2 Special Parameters of the POSIX standard defines a list of special characters we should interpret:

• ? - Expands to the decimal exit status of the most recent pipeline.
• - - Expands to the current option flags.
• $ - Expands to the decimal process ID of the invoked shell.
  In a subshell (see Shell Execution Environment ), '$' shall expand to the same value as that of the current shell.
• ! - Expands to the decimal process ID of the most recent background command (see Lists) executed from the current shell.
• 0 - Expands to the name of the shell or shell script.
• # - Expands to the decimal number of positional parameters.
• • @ - Expands to the positional parameters, starting from one, initially producing one field for each positional parameter that is set.
• * - Expands to the positional parameters, starting from one, initially producing one field for each positional parameter that is set. Read more in 2.5.2.