In an interactive session, the command interpreter accepts the shortest unambiguous abbreviation for any command. Since the interpreter is built on the Tcl language, some possible XSPEC command abbreviations might coincide with both XSPEC and Tcl commands. In this case, the interpreter will print the multiple possibilities and stop. Command abbreviations may be specified in a start-up script ($HOME/.xspec/xspec.rc), see Appendix A for details.
Inside a script, command abbreviations are not recognized. This behavior can be overridden, but we do not recommended it. However, specific abbreviations can be defined in the custom startup script.
Operating-system commands can be given from within XSPEC simply by typing the command, as at the shell prompt: however, if wild cards are needed (e.g. ls *.pha) the operating system command must be preceded by syscall. Note that system commands have precedence so an XSPEC abbreviation which corresponds to a system command will run the latter.