There are a number of variables provided by the Korn shell that allow you to customize your working environment. Some are automatically set by the Korn shell, some have a default value if not set, while others have no value unless specifically set.
| CDPATH | search path for cd when not given a full pathname (no default) |
| COLUMNS | window width for in-line edit mode and select command lists (default 80) |
| EDITOR | pathname of the editor for in-line editing (default /bin/ ed) |
| ENV | pathname of the environment file (no default) |
| FCEDIT | default editor for the fc command |
| FPATH | search path for auto-loaded functions pathname of the history file |
| HISTFILE | pathname of the history file (default $HOME/ .sh_history) |
| HISTSIZE | number of commands to save in history file (default 128) |
| HOME | home directory |
| IFS | internal field separator (default space, tab, newline) |
| LINES | specifies column length for select lists |
| MAIL | name of mail file |
| MAILCHECK | specifies how often to check for mail (default 600 seconds) |
| MAILPATH | search path for mail files (no default) |
| OLDPWD | previous working directory |
| OPTARG | value of the last getopts option argument |
| OPTIND | index of the last getopts option argument |
| PATH | search path for commands (default /bin:/usr/bin:) |
| PPID | process id of the parent shell |
| PS1 | primary prompt string (default $, #) |
| PS2 | secondary prompt string (default >) |
| PS3 | select command prompt (default #?) |
| PS4 | debug prompt string (default +) |
| RANDOM | contains a random number |
| REPLY | contains input to read command when no variables given |
| SECONDS | contains number of seconds since Korn shell invocation |
| SHELL | pathname of shell |
| TERM | specifies your terminal type (no default) |
| TMOUT | Korn shell timeout variable (default 0) |
| VISUAL | pathname of the editor for in-line editing |