HP-UX Reference (11i v3 07/02) - 1 User Commands A-M (vol 1)

k
ksh(1) ksh(1)
command in the replaced text, other than any that are in the process of being replaced, is tested for addi-
tional aliases. If the last character of the alias value is a blank, the word following the alias is also checked
for alias substitution.
Aliases can be used to redefine special built-in commands, but cannot be used to redefine the keywords
listed above. Aliases can be created, listed, and exported with the
alias command and can be removed
with the
unalias command. Exported aliases remain in effect for subshells but must be reinitialized for
separate invocations of the shell (see Invoking ksh below).
Aliasing is performed when scripts are read, not while they are executed. Therefore, for it to take effect,
alias must be executed before the command referring to the alias is read.
Aliases are frequently used as a shorthand for full path names. An option to the aliasing facility allows the
value of the alias to be automatically set to the full path name of the corresponding command. These
aliases are called tracked aliases. The value of a tracked alias is defined the first time the identifier is
read and becomes undefined each time the
PATH variable is reset. These aliases remain tracked so that
the next reference redefines the value. Several tracked aliases are compiled into the shell. The
-h option
of the
set command converts each command name that is an identifier into a tracked alias.
The following exported aliases are compiled into the shell but can be unset or redefined:
autoload=’typeset -fu’
false=’let 0’
functions=’typeset -f’
hash=’alias -t -’
history=’fc -l’
integer=’typeset -i’
nohup=’nohup ’
r=’fc -e -’
stop=’kill -STOP’
suspend=’kill -STOP $$’
true=’:’
type=’whence -v’
Tilde Substitution
After alias substitution is performed, each word is checked to see if it begins with an unquoted
˜. If it does,
the word up to a
/ is checked to see if it matches a user name in the
/etc/passwd file. If a match is
found, the
˜ and the matched login name are replaced by the login directory of the matched user. This is
called a tilde substitution. If no match is found, the original text is left unchanged. A
˜, alone or before a
/, is replaced by the value of the HOME parameter. A ˜ followed by a +
or - is replaced by the value of
the parameter
PWD and OLDPWD, respectively. In addition, tilde substitution is attempted when the value
of a parameter assignment begins with a ˜.
Command Substitution
The standard output from a command enclosed in parenthesis preceded by a dollar sign ($(command
))or
a pair of back single quotes (accent grave) (
‘command‘) can be used as part or all of a word; trailing new-
lines are removed. In the second (archaic) form, the string between the quotes is processed for special quot-
ing characters before the command is executed (see Quoting below). The command substitution $(cat
file)
can be replaced by the equivalent but faster $(<file).
Command substitution of most special commands (built-ins) that do not perform I/O redirection are carried
out without creating a separate process. However, command substitution of a function creates a separate
process to execute the function and all commands (built-in or otherwise) in that function.
An arithmetic expression enclosed in double parentheses preceded by a dollar sign ($((expression)))is
replaced by the value of the arithmetic expression within the double parentheses (see Arithmetic Evalua-
tion below for a description of arithmetic expressions).
Parameter Substitution
A parameter is an identifier, one or more digits, or any of the characters *, @, #, ?, -, $, and !.A
named parameter (a parameter denoted by an identifier) has a value and zero or more attributes. Named
parameters can be assigned values and attributes by using the
typeset special command. Attributes
supported by ksh are described later with the typeset special command. Exported parameters pass
values and attributes to the environment.
HP-UX 11i Version 3: February 2007 − 3 − Hewlett-Packard Company 491