What are the special dollar sign shell variables

Question

In Bash  there appear to be several variables which hold special  consistently-meaning values  For instance     myprogram  amp   echo      will return the PID of the process which backgrounded myprogram  I know of others  such as    which I think is the current TTY  Are there others

User · Answer

Take care with some of the examples   0 may include some leading path as well as the name of the program  Eg save this two line script as   mytry sh and the execute it      bin bash  echo  parameter 0 -- gt   0    exit 0   Output   parameter 0 -- gt    mytry sh   This is on a current  year 2016  version of Bash  via Slackware 14 2

User · Answer

To help understand what do      0 and  1        n do  I use this script      bin bash  for   i 0  i lt      i      do   echo  parameter  i -- gt     i   done   Running it returns a representative output       myparams sh  hello   how are you   i am fine  parameter 0 -- gt  myparams sh parameter 1 -- gt  hello parameter 2 -- gt  how are you parameter 3 -- gt  i am fine

User · Answer

1   2   3      are the positional parameters       is an array-like construct of all positional parameters    1   2   3            is the IFS expansion of all positional parameters   1  2  3         is the number of positional parameters   - current options set for the shell     pid of the current shell  not subshell      most recent parameter  or the abs path of the command to start the current shell immediately after startup    IFS is the  input  field separator     is the most recent foreground pipeline exit status     is the PID of the most recent background command   0 is the name of the shell or shell script    Most of the above can be found under Special Parameters in the Bash Reference Manual  There are all the environment variables set by the shell   For a comprehensive index  please see the Reference Manual Variable Index

User · Answer

last argument of last command    number of arguments passed to current script         list of arguments passed to script as string   delimited list   off the top of my head  Google for bash special variables

[bash] What are the special dollar sign shell variables?

Examples related to bash

Examples related to environment-variables

Examples related to dollar-sign