Variables set by the Korn shell or POSIX shell
The following are variables that are set by the shell.
| Item | Description |
|---|---|
| underscore (_) | Indicates initially the absolute path name of the shell or script being executed as passed in the environment. Subsequently, it is assigned the last argument of the previous command. This parameter is not set for commands that are asynchronous. This parameter is also used to hold the name of the matching MAIL file when checking for mail. |
| ERRNO | Specifies a value that is set by the most recently failed subroutine. This value is system-dependent and is intended for debugging purposes. |
| LINENO | Specifies the line number of the current line within the script or function being executed. |
| OLDPWD | Indicates the previous working directory set by the cd command. |
| OPTARG | Specifies the value of the last option argument processed by the getopts regular built-in command. |
| OPTIND | Specifies index of the last option argument processed by the getopts regular built-in command. |
| PPID | Identifies the process number of the parent of the shell. |
| PWD | Indicates the present working directory set by the cd command. |
| RANDOM | Generates a random integer, uniformly distributed between 0 and 32767. The sequence of random numbers can be initialized by assigning a numeric value to the RANDOM variable. |
| REPLY | Set by the select statement and by the read regular built-in command when no arguments are supplied. |
| SECONDS | Specifies the number of seconds since shell invocation is returned. If this variable is assigned a value, then the value returned upon reference will be the value that was assigned plus the number of seconds since the assignment. |