tasker

'tasker' is a simple build tool which uses a native bash DSL. It is perfect for small Java projects when you can't be bothered setting up Maven, small c/c++ projects when you don't want to brush up on makefiles (again).

Elements of a 'tasker' script

task block (required) defines a task

task build_it
    ...
endtask

doc section (not required) - adds a short description of the task,

task build_it
    doc "Task to build the thing"
endtask

depends section (not required) - lists tasks to be done before this one,

task build_it
    depends clean_up generate_files
endtask

met block (not required) - test if this task needs to be run, and that the execution was successful after running. The following example checks if the build directory already exists before trying to create it. A task will fail if the 'met' block doesn't pass after executing the 'meet' block. The statements can be on multiple lines, the return value from the last statement determines if the task has been met or not (but the extra semicolon is required if it's all on one line).

task make_build_directory
    met() { test -d build; }
    ...
endtask

meet block (not required) - contains commands to complete the task

task make_build_directory
    meet() {
        mkdir build
    }
endtask

Example

In the following example;

• The run-and-clean task just requires that the tasks run and clean are executed.
• The build task creates an executable shell script. It only runs if an executable script named 'message.sh' doesn't already exist. It also verifies that the script exists after running.
• The run task requires that the build task has run, then runs the 'message.sh' shell script.
• The cleanup task deletes 'message.sh' if it hasn't already been deleted, then checks that it has gone afterwards.

. tasker.sh

task run-and-clean
    doc "Task to build and run 'hello'"
    depends run clean
endtask

task build
    doc "Create shell script"
    met() { test -x message.sh; }
    meet() {
        echo "#!/bin/bash" > message.sh
        echo "echo Hello" >> message.sh
        chmod +x message.sh
    }
endtask

task run
    doc "Run the shell script"
    depends build
    meet() {
        ./message.sh
    }
endtask

task clean
    doc "Cleanup"
    met() { test ! -f message.sh; }
    meet() {
        rm message.sh
    }
endtask

The output looks like this,

Johns-Mac:tasker jdoxey$ ./example.sh run-and-clean
tasker: [run-and-clean] No met block, checking dependencies...
tasker:  |   [run] No met block, checking dependencies...
tasker:  |    |   [build] Not met, checking dependencies...
tasker:  |    |   [build] ...no dependencies, doing meet...
tasker:  |    |   [build] ...all done, verifying...
tasker:  |    |   [build] ...satisfied met, nice.
tasker:  |   [run] ...dependencies sorted, doing meet...
Hello
tasker:  |   [run] ...all done, verifying...
tasker:  |   [run] ...no met to verify, all done.
tasker:  |   [clean] Not met, checking dependencies...
tasker:  |   [clean] ...no dependencies, doing meet...
tasker:  |   [clean] ...all done, verifying...
tasker:  |   [clean] ...satisfied met, nice.
tasker: [run-and-clean] ...dependencies sorted, doing meet...
tasker: [run-and-clean] ...no meet, verifying...
tasker: [run-and-clean] ...no met to verify, all done.

Bash cheat sheet

Bash can be a bit strange, below are some notes which help me remember the weird bits.

• You can test values in bash with,
  • test - check for files, compare strings, (and some awkward integer comparisons). For example test -x script.sh checks that an executable file called "script.sh" exists. Check man test for details.
  • [ expression ] - single square bracket expressions are the same as using the 'test' command. E.g. test -f file.txt is the same as [ -f file.txt ]. (I usually find test ... more readable than this shorthand).
  • [[ expression ]] - double square brackets are a bash built-in. They are similar to test and single square brackets except you can also do regex matching with '=~', and you can combine expressions with && and ||. For documentation, see 'man bash' and search for '[[ expression ]]'.
  • ((expression)) - double round brackets are for arithmetic (numeric) expressions. Check man bash and look for the ARITHMETIC EVALUATION section.
  • (commands) - commands in single round brackets are executed in a sub-shell, they are NOT usually used for testing conditions.
• In bash, a 0 return value is a SUCCESS, any non-zero value is an ERROR. One mnemonic goes, "In bash there is one way to succeed, and many ways to fail".

ToDo

• Print 'doc' descriptions when you type 'help' (or '-h' or '--help' or '-help')
• Be able to designate a 'default' task (chosen if you don't specify a target)
• Dial down logging (with option to turn it back up)