Programming
Process
This list is not linear, at any point it may be necessary to go back to a previous step.
- understanding
- research the problem
- specification
- platform, inputs, outputs, interface, size, speed, etc.
- design/development
- decide on data representation, structure, algorithms, etc. before coding
- prototyping
- incomplete coding just sufficient to verify design
- implementation
- complete coding
- documentation
- description of usage, design, coding, etc.
- necessary for users, maintainers, other programmers, and yourself
- testing
- in house
- alpha: work in progress, limited set of outside testers
- beta: feature complete, larger set of outside testers
- release candidate: ready for release if no major bugs are found
- release
- good enough for distribution
- maintenance
- bug fixes, enhancements, occasional redesign
- end of life
- no longer worth maintaining
Design Hints
- reuse existing components
- outline your solution before coding
- code the smallest possible increment, test and debug, save with a different name
- anticipate error conditions and deal with them gracefully
- strive for simplicity and clarity
- document your code
Shell Control Flow
- procedural
- no objects, threads, first-class functions, etc.
- selection
- chooses between alternative actions
- iteration
- repeats an action
- call
- transfers control to another part of the program, then returns
Shell Data Types
Primative
- character
- ASCII, Unicode
- numeric
- integer
- floating point in ksh, zsh
- stored as character strings
Composite
- array
- ordered, indexed, used for random access
- integer indexes
- associative arrays (character indexes) in ksh, bash, zsh
- string
- similar to an array of characters
Shell Script Execution
- interpreted
- not compiled, runs in shell process
- slow
- dynamic
- declarations not required, automatic memory management
- weak typing
- operations can convert types
- variable values stored as strings
- executing a shell script
bash script.bash arg(s) # runs in subshellsource script.bash arg(s) # runs in current shell. script.bash arg(s) # runs in current shellchmod a+x script.bash # make executable./script.bash arg(s) # runs in subshell