z/OS V1R9.0 UNIX System Services Command ... - Christian Grothoff

Quoting can override the special meanings of reserved words and aliases. For
example, in:
"time" program
the quotes around time tell the shell not to interpret time as a shell reserved word.
Instead, sh does a normal command search for a command named time.
You must always quote the following characters if you want sh to interpret them
literally:
| & ; < > ( ) $ ' " ` \
The following characters need to be quoted in certain contexts if they are to be
interpreted literally:
* ? [ # % =
~
Directory Substitution
When a word begins with an unquoted tilde ( ~), sh tries to perform directory
substitution on the word.sh obtains all characters from the tilde (~) to the first slash
(/) and uses this as a user name. sh looks for this name in the user profile, the file
that contains information on all the system’s users. If sh finds a matching name, it
replaces ~name with the name of the user’s home directory, as given in the
matching RACF user profile entry.
For example, if you specify a filename as:
~jsmith/file
sh would look up jsmith’s home directory and put that directory name in place of
the ~jsmith construct.
If you specify a ~without an accompanying name, sh replaces the ~with the current
value of your HOME variable. For example:
echo ~
displays the name of your home directory. Similarly, sh replaces the construct ~+
with the value of the PWD variable (the name of the your working directory), and
replaces the tilde hyphen (~–) with the value of OLDPWD (the name of your
previous working directory). In variable assignments, tilde expansion is also
performed after colons (:).
Parameter Substitution
The shell uses three types of parameters: positional parameters, special
parameters, and variables. A positional parameter is represented with either a single
digit (except 0) or one or more digits in braces. For example, 7 and {15} are both
valid representations of positional parameters. Positional parameters are assigned
values from the command line when you invoke sh.
A special parameter is represented with one of the following characters:
* @ # ? ! - $ 0
The values to which special parameters expand are listed in the following
paragraphs.
sh
Chapter 2. Shell command descriptions 559