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Static Job Specification Synopsis
Tractor Job files are typically represented as TCL scripts using special job definition operators recognized by the Tractor job parser. This format was first introduced for the Alfred system, and Tractor remains compatible with nearly all Alfred constructs.
Tractor also supports an evolving set of JSON job specification formats, described in a separate document.
Tractor job input scripts (in alfscript format) are composed of expressions using the following Tcl operators:
Job [options] Task {title} [options] RemoteCmd {launch_expr} [options] Cmd {launch_expr} [options] Instance {task_title_to_reference} Iterate varname -from n -to m -by i -template {script} [options] Assign varname {value_string}
See the Operator Details for detailed descriptions of options and operator syntax.
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- launch expressions are tokenized and passed directly to execvp(2); hence semi-colon separated command sequences, command pipelines, environment variable references, and filename meta-characters (e.g. *,?,[]) are not directly supported (instead use an appropriate sub-shell).
- Tractor (and Alfred) will do tilde-expansion, as in csh
- single-quotes have no special meaning (i.e. they don't group words together), use braces - {} - for grouping.
- only one tokenizing pass is made through each argument string.
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Cmd {find ~bob -type f -name preview.* -exec /bin/rm \{\} ;}
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Given the restrictions just described above on Cmd launch expressions there are nonetheless occasions when shell constructs, such as command pipelines or run-time filename expansion, can be very useful. In these situations, a simple solution is to launch an appropriate shell as the Cmd, passing the pipeline expression to the shell via command-line arguments:
Cmd {/bin/sh -e "cd /tmp/frames; ls -1 | xargs -I+ cp + /DDR"}
Script authors should read the documentation for their shell of choice to understand the implications of various invocation options. For example, you must decide whether the user's .cshrc or .profile should be executed when the dispatcher launches a command like the above.
Another approach is to use the Cmd -msg option to pass arbitrary expressions to a launched shell. This is essentially equivalent to the above approach, but not as compact; however, it does allow for persistent reuse of the shell, if that's desired. Consider the following examples which send mail, which can sometimes be handy at the end of job. Recall that the -s option to Mail looks for the next "word" as the subject, so spaces need to be escaped (using csh(1) syntax this time):
Cmd {/bin/csh -fc "/usr/sbin/Mail -s 'job done' jean < ~/errlog"}
Cmd {/bin/csh -fet} -msg {/usr/sbin/Mail -s 'job done' jean < ~/errlog}
Often the simplest solution for complex expressions is to write a short shell script in your favorite language and launch the script from Tractor:
Cmd {myscript}
If a remote server is required, the run-time host selection can be passed to the script as an argument:
Cmd {myscript %h} -service {someServerType}
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