HP-UX Reference (11i v1 05/09) - 1 User Commands N-Z (vol 2)

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sh-posix(1) sh-posix(1)
• Setting the value of SHELL,
ENV,orPATH
• Specifying path or command names containing /
• Redirecting output (>, >|,
<>, and >>)
The restrictions above are enforced after the
.profile
and ENV files are interpreted.
When a command to be executed is found to be a shell procedure,
rsh invokes sh to execute it. Thus, the
end-user is provided with shell procedures accessible to the full power of the standard shell, while being
restricted to a limited menu of commands. This scheme assumes that the end-user does not have write and
execute permissions in the same directory.
These rules effectively give the writer of the
.profile file complete control over user actions, by per-
forming guaranteed set-up actions and leaving the user in an appropriate directory (probably not the login
directory).
The system administrator often sets up a directory of commands (usually
/usr/rbin) that can be safely
invoked by
rsh. HP-UX systems provide a restricted editor
red (see ed(1)), suitable for restricted users.
Definitions
metacharacter One of the following characters:
;&()|<>newline space tab
blank A tab or a space.
identifier A sequence of letters, digits, or underscores starting with a letter or underscore.
Identifiers are used as names for functions and named parameters.
word A sequence of characters separated by one or more nonquoted metacharacters.
command A sequence of characters in the syntax of the shell language. The shell reads each
command and carries out the desired action, either directly or by invoking separate
utilities.
special command A command that is carried out by the shell without creating a separate process.
Except for documented side effects, most special commands can be implemented as
separate utilities.
# Comment delimiter. A word beginning with # and all following characters up to a
newline are ignored.
parameter An identifier, a decimal number, or one of the characters !, #
, $, *, -, ?, @, and _.
See the "Parameter Substitution" subsection.
named parameter A parameter that can be assigned a value. See the "Parameter Substitution" subsec-
tion.
variable A parameter.
environment variable
A parameter that is known outside the local shell, usually by means of the
export
special command.
Commands
A command can be a simple command that executes an executable file, a special command that executes
within the shell, or a compound command that provides flow of control for groups of simple, special, and
compound commands.
Simple Commands
A simple command is a sequence of blank-separated words that may be preceded by a parameter assign-
ment list. (See the "Environment" subsection). The first word specifies the name of the command to be
executed. Except as specified below, the remaining words are passed as arguments to the invoked com-
mand. The command name is passed as argument 0 (see exec(2)). The value of a simple-command is its
exit status if it terminates normally, or 128+errorstatus if it terminates abnormally (see signal(5) for a list
of errorstatus values).
A pipeline is a sequence of one or more commands separated by a bar (|) and optionally preceded by an
exclamation mark (!). The standard output of each command but the last is connected by a pipe (see
pipe(2)) to the standard input of the next command. Each command is run as a separate process; the shell
waits for the last command to terminate. If ! does not precede the pipeline, the exit status of the pipeline
HP-UX 11i Version 1: September 2005 − 2 − Hewlett-Packard Company Section 1−−893