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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.
Special Variables
| 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) |
| ERRNO | error number returned by most recently failed system call (system dependent) |
| 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 the command history file (default 128) |
| HOME | home directory |
| IFS | internal field separator (default space, tab, newline) |
| LINES | specifies column length for select lists |
| 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 the input to the read command when no variables are 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 |
One-dimensional arrays are supported by the Korn shell. On most systems, arrays can have a maximum of 512 elements. Array subscripts start at 0 and go up to 511. Any variable can become an array by simply referring to it with a subscript.
Array Variable Assignment Format
| variable[0]=value variable[1]=value ... variable[n]=value | |
| set –A variable value0 value1 ... valuen | |
| typeset variable[0]=value variable[1]=value ... variable[n]=value | assign values to array variable elements |
| set +A variable value0 value1 ... valuen | reassign values to array variable elements |
| typeset –attributes variable[0]=value variable[1]=value ... variable[n]=value | assign attributes and values to array variable elements |
| typeset –attributes variable | assign attributes to array variable |
| typeset +attributes variable | remove attributes from array variable (except readonly) |
Array Variable Evaluation
| ${array}, $array | array element zero |
| ${array[n]} | array element n |
| ${array[*]}, ${array[@]} | all elements of an array |
| ${#array[*]}, ${#array[@]} | number of array elements |
| ${#array[n]} | length of array element n |
| $(command) | replace with the standard output of command |
| $((arithmetic-expression) | replace with the result of arithmetic-expression |
| $(<file) | replace with the contents of file |
| `command` | replace with the standard output of command (provided for compatibility with the Bourne shell) |
| ~ | replace with $HOME |
| ~user | replace with the home directory of user |
| ~– | replace with $OLDPWD (previous directory) |
| ~+ | replace with $PWD (current directory) |
Quotes are used when assigning values containing whitespace or special characters, to delimit variables, and to assign command output. They also improve readability by separating arguments from commands.
| '...' | remove the special meaning of enclosed characters except ' |
| "..." | remove the special meaning of enclosed characters except $, ', and \ |
| \c | remove the special meaning of character c |
| `command` | replace with the standard output of command (provided for compatibility with the Bourne shell) |
In-line editing provides the ability to edit the current or previous commands before executing them. There are three in-line editing modes available: emacs, gmacs, and vi. The emacs and gmacs modes are basically the same, except for the way Ctl-t is handled. The in-line editing mode is specified by setting the EDITOR or VISUAL variables, or with the set –o command. The editing window width is specified by the COLUMNS variable. For lines longer than the window width, a mark is displayed to notify position. The marks >, <, and * specify that the line extends to the right, left, or both sides of the window.
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