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

sh
$(command)
as in:
ed $(grep –f –l function $(find . –name ’*.c’))
This command uses find to search the current directory and its subdirectories to
find all files, the names of which end in .c. It then uses grep –f to search each such
file for those that contain the string function. Finally, it calls ed to edit each such
file.
There is a historical inconsistency in the backquoting syntax. A backslash (\) within
a backquoted command is interpreted differently depending on its context.
Backslashes are interpreted literally unless they precede a dollar sign ($), grave
accent (`), or another backslash (\). In these cases, the leading backslash
becomes an escape character to force the literal interpretation of the $, `, or \.
Consequently, the command:
echo ’\$x’
issued at system level produces the output:
\$x
whereas the same command nested in a backquoted syntax:
echo `echo ’\$x’`
produces the output:
$x
We recommend the $(command) syntax for command substitutions.
sh performs command substitutions as if a new copy of the shell is invoked to run
the command. This affects the behavior of $− (standing for the list of options passed
to the shell). If a command substitution contains $−, the expansion of $− does not
include the –i option, since the command is being run by a non-interactive shell.
File Descriptors and Redirection
The shell sometimes refers to files using file descriptors. A file descriptor is a
number in the range 0 to 9. It may have any number of digits. For example, the file
descriptors 001 and 01 are identical to file descriptor 1. Various operations (for
example, exec) can associate a file descriptor with a particular file.
Some file descriptors are set up at the time the shell starts up. These are the
standard input/output streams:
v Standard input (file descriptor 0)
v Standard output (file descriptor 1)
v Standard error (file descriptor 2)
Commands running under the shell can use these descriptors and streams too.
When a command runs under the shell, the streams are normally associated with
your terminal. However, you can redirect these file descriptors to associate them
with other files (so that I/O on the stream takes place on the associated file instead
of your terminal). In fact, the shell lets you redirect the I/O streams associated with
file descriptors 0 through 9, using the following command-line constructs.
564 z/OS V1R9.0 UNIX System Services Command Reference