Enhanced Korn shell (ksh93)

$ myvar=( x=1 y=2 ) 
$ print "${myvar.x}" 
1

$ numbers=( zero one two three ) 
$ print ${numbers[0]} ${numbers[3]} 
zero three   

$ greeting="hello"
$ typeset -n welcome=greeting     # establishes the reference 	
$ welcome="hi there"              # overrides previous value 	
$ print $greeting 	
hi there   

• ${!varname} is the name of the variable itself.
• ${!varname[@]} names the indexes for the varname array.
• ${param:offset} is a substring of param, starting at offset.
• ${param:offset:num} is a substring of param, starting at offset, for num number of characters.
• ${@:offset} indicates all positional parameters starting at offset.
• ${@:offset:num} indicates num positional parameters starting at offset.
• ${param/pattern/repl} evaluates to param, with the first occurrence of pattern replaced by repl.
• ${param//pattern/repl} evaluates to param, with every occurrence of pattern replaced by repl.
• ${param/#pattern/repl} if param begins with pattern, then param is replaced by repl.
• ${param/%pattern/repl} if param ends with pattern, then param is replaced by repl.

• The varname.get function is invoked every time varname is referenced. If the special variable .sh.value is set within this function, then the value of varname is changed to this value. A simple example is the time of day:

  $ function time.get 
  > { 
  >     .sh.value=$(date +%r) 
  > } 
  $ print $time 
  09:15:58 AM 
  $ print $time    # it will change in a few seconds 
  09:16:04 AM

• The varname.set function is invoked every time varname is set. The .sh.value variable is given the value that was assigned. The value assigned to varname is the value of .sh.value when the function completes. For example:

  $ function adder.set 
  > { 
  >   let .sh.value="
  $ {.sh.value} + 1" 
  > } 
  $ adder=0 
  $ echo $adder 
  1 
  $ adder=$adder 
  $ echo $adder 
  2  

• The varname.unset function is executed every time varname is unset. The variable is not actually unset unless it is unset within the function itself; otherwise it retains its value.

Within all discipline functions, the special variable .sh.name is set to the name of the variable, while .sh.subscript is set to the value of the variables subscript, if applicable.

• If the command to be executed is not found, the return value is set to 127.
• If the command to be executed is found, but not executable, the return value is 126.
• If the command is executed, but is terminated by a signal, the return value is 256 plus the signal number.

• The builtin command lists all available built-in commands.
• The printf command works in a similar manner as the printf() C library routine. See the printf command.
• The disown blocks the shell from sending a SIGHUP to the specified command.
• The getconf command works in the same way as the stand-alone command /usr/bin/getconf. See the getconf command.
• The read built-in command has the following flags:
  • read -d {char} allows you to specify a character delimiter instead of the default newline.
  • read -t {seconds} allows you to specify a time limit, in seconds, after which the read command will time out. If read times out, it will return FALSE.
• The exec built-in command has the following flags:
  • exec -a {name} {cmd} specifies that argument 0 of cmd be replaced with name.
  • exec -c {cmd} tells exec to clear the environment before executing cmd.
• The kill built-in command has the following flags:
  • kill -n {signum} is used for specifying a signal number to send to a process, while kill -s {signame} is used to specify a signal name.
  • kill -l, with no arguments, lists all signal names but not their numbers.
• The whence built-in command has the following flags:
  • The -a flag displays all matches, not only the first one found.
  • The -f flag tells whence not to search for any functions.
• An escape character sequence is used for use by the print and echo commands. The Esc (Escape) key can be represented by the sequence \E.
• All regular built-in commands recognize the -? flag, which shows the syntax for the specified command.
• The getopts built-in requires optstring to contain a leading + to allow options beginning with a + symbol.

To enable the auditing feature in the enhanced Korn shell, complete the following steps:

• To enable the auditing feature in the ksh93u command, the /etc/ksh_audit file must have an output filename an identification value for the user. For example, /tmp/ksh_auditfile;205;0.
• You can configure the auditing feature to generate a detailed record for every executable command. You can use the record to monitor, track, and audit activities for one or more users on a system, including the system administrators.
• To enable the auditing feature in the ksh93 command, the file /etc/ksh_audit must be created and configured by specifying the location of the audit_log file and an identification value for the user. You can separate the identification values by using a semicolon.

For example, the text /tmp/ksh_auditfile;0;100;205 in the /etc/ksh_audit file refers to the location of the log file (/tmp/ksh_auditfile), and the user identification values which are, 0 (root), 100, and 205 respectively.

• With Korn shell ksh93, you cannot export functions using the typeset -fx built-in command.
• With Korn shell ksh93, you cannot export an alias using the alias -x built-in command.
• With Korn shell ksh93, a dollar sign followed by a single quote ($') is interpreted as an ANSI C string. You must quote the dollar sign (\"$\"') to get the old (ksh) behavior.
• Argument parsing logic for Korn shell ksh93 built-in commands has been changed. The undocumented combinations of argument parsing to Korn shell ksh built-in commands do not work in Korn shell ksh93. For example, typeset -4i works similar to typeset -i4 in Korn shell ksh, but does not work in Korn shell ksh93.
• With Korn shell ksh93, command substitution and arithmetic expansion is performed on special environment variables PS1, PS3, and ENV while expanding. Therefore, you must escape the grave symbol (`) and the dollar sign and opening parenthesis symbols ($() using a backslash (\) to retain the old behavior. For example, Korn shell ksh literally assigns x=$'name\toperator' as $name\toperator; Korn shell ksh93 expands \t and assigns it as name<\t expanded>operator. To preserve the Korn shell ksh behavior, you must quote $. For example, x="$"'name\toperator'.
• The ERRNO variable has been removed in Korn shell ksh93.
• In Korn shell ksh93, file names are not expanded for non-interactive shells after the redirection symbol.
• With Korn shell ksh93, you must use the -t option of the alias command to display tracked aliases. The tracked alias feature is now obsolete, so the displayed aliases might not be tracked.
• With Korn shell ksh93, in emacs mode, Ctrl+T swaps the current and previous character. With ksh, Ctrl+T swaps the current and next character.
• Korn shell ksh93 does not allow unbalanced parentheses within ${name operator value}. For example, ${name-(} needs an escape such as ${name-\(} to work in both versions.
• With Korn shell ksh93, the kill -l command lists only the signal names, not their numerical values.