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DESCRIPTION
The external machid commands return a true or false value. Machid is not a command itself but refers to a set of commands. These commands are used to identify the hardware you are using. They are usually used in shell scripts to provide portability. If the machid command you use has a return value of zero (0), you are using the hardware described by the command name . The following example is a typical shell script coding:
if vax | # If on a vax computer, |
then cd /usr/lib/vax | # change directories to vax one |
else cd /usr/lib/other | # else change dir to other one |
fi | # end the if conditional. |
COMMAND FORMAT
Following is the general format of each machid command.
pdp11 | True if on a DEC PDP-11/45 or PDP-11/70 computer. |
u3b | True if on an AT&T 3B20 computer. |
u3b2 | True if on an AT&T 3B2 computer. |
u3b5 | True if on an AT&T 3B5 computer. |
u3b15 | True if on an AT&T 3B15 computer. |
sun | True if on a Sun Microsystems computer. |
sun3 | True if on a Sun model 3 computer. |
sun4 | True if on a Sun model 4 (SPARC ) computer. |
vax | True if on a DEC VAX-11/750 or VAX-11/780 computer. |
u370 | True if on an IBM System/370 computer. |
NOTE:
Not all vendors implement all of the commands. Usually the vendor only implements the more common hardware types and one for the vendor s own hardware.
RELATED COMMANDS
Refer to the test command described in Module 135.
RELATED FILES
The machid commands do no return output, they simply provide return codes.
RETURN CODES
The machid commands return a true (zero) value if you are on the type of machine the command describes. If you are NOT on the machine described by the command name, then a false (nonzero) value is returned.
APPLICATIONS
These commands are used in shell scripts to provide portability across different types of hardware. Shell scripts can be coded to handle different hardware device paths, different command formats, and various other system dependencies. The machid commands are useful in a make file to control how a program is compiled. In some cases the uname command, described in Module 148, can be used to perform the same task. If uname is used, the test command must be used to check for specific strings being returned.
TYPICAL OPERATION
In this activity you use the machid commands to display what type of system you are using. Begin at the shell prompt.
cj> for CMDTYPE in u3b2 u3b5 vax do if $CMDTYPE then echo You are using a $CMDTYPE machine! fi done
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