The ZSYSTEM command creates a child of the current process.
The format of the ZSYSTEM command is:
ZSY[STEM][:tvexpr] [expr][,...]]
The optional truth-valued expression immediately following the command is a command postconditional that controls whether or not GT.M executes the command.
The optional expression specifies the command passed to the shell; after processing the command, the shell returns control to GT.M. The maximum length for the optional expression is 4K bytes.
An indirection operator and an expression atom evaluating to a list of one or more ZSYSTEM arguments form a legal argument for a ZSYSTEM.
The ZSYSTEM command creates a new process and passes its argument to a shell for execution. The new process executes in the same directory as the initiating process using the shell specified by the SHELL environment variable, or if that is not defined, the default shell (typically Bourne). The new process has the same operating system environment, such as environment variables and input/output devices, as the initiating process. The initiating process pauses until the new process completes before continuing execution. After control returns to GT.M, $ZSYSTEM contains the return status of the forked process.
A ZSYSTEM with a null argument creates a shell with the standard input and output devices. When the shell exits, control is returned to GT.M. For an interactive process, both stdin and stdout are generally the user's terminal, in which case the shell prompts for input until provided with an exit command. A ZSYSTEM with no arguments must be followed by two (2) spaces before any following command on the same line and is equivalent to a ZSYSTEM with a single null string argument.
If a ZSYSTEM command has multiple arguments, it starts a new process for each argument, one at a time. ZSYSTEM waits for one process to complete before starting the next one.
A ZSYSTEM command within a TP transaction, violates the property of Isolation. Consequently because of the way that GT.M implements transaction processing, a ZSYSTEM within a transaction may suffer an indefinite number of restarts ("live lock").
An indirection operator and an expression atom evaluating to a list of one or more ZSYSTEM arguments form a legal argument for a ZSYSTEM.
![[Note]](images/note.jpg) |
Note |
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PIPE devices are frequently a better alternative to ZSYSTEM commands as they have timeouts, can perform controlled co-processing, easily return more information and are more efficient where you need multiple operations. |
Example:
GTM>zsystem "ls *.m"
This uses ZSYSTEM to fork a process that then performs the ls command with *.m as an argument to ls. Once the command completes, the forked process terminates.
GTM>zsystem "echo 'hello world'" hello world
This examples show a possible use of quoting with ZSYSTEM to run the echo command.
Example:
GTM>zsystem $
This ZSYSTEM has no argument so the forked process prompts for input.