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The /usr/xpg4/bin/sh utility is a standards compliant shell. This utility provides all the functionality of /usr/bin/ksh, except in cases discussed below where differences in behavior exist. See Arithmetic Expansions section for details.
/usr/bin/ksh is a command and programming language that executes commands read from a terminal or a file. rksh is a restricted version of the command interpreter ksh; it is used to set up login names and execution environments whose capabilities are more controlled than those of the standard shell. See Invocation below for the meaning of arguments to the shell.
Definitions
; & ( ) < > NEWLINE SPACE TAB
A blank is a TAB or a SPACE. An identifier is a sequence of letters, digits, or underscores starting with a letter or underscore. Identifiers are used as names for functions and variables. A word is a sequence of characters separated by one or more non-quoted metacharacters.
A command is 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. A special-command is 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.