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172 lines
8.6 KiB
Markdown
172 lines
8.6 KiB
Markdown
[This document is formatted with GitHub-Flavored Markdown. ]: #
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[For better viewing, including hyperlinks, read it online at ]: #
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[https://github.com/kvz/bash3boilerplate/blob/HEAD/FAQ.md ]: #
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## Contents
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- [What is a CLI](#what-is-a-cli)?
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- [How do I incorporate BASH3 Boilerplate into my own project](#how-do-i-incorporate-bash3-boilerplate-into-my-own-project)?
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- [How do I add a command-line flag](#how-do-i-add-a-command-line-flag)?
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- [How do I access the value of a command-line argument](#how-do-i-access-the-value-of-a-command-line-argument)?
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- [What is a magic variable](#what-is-a-magic-variable)?
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- [How do I submit an issue report](#how-do-i-submit-an-issue-report)?
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- [How can I contribute to this project](#how-can-i-contribute-to-this-project)?
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- [Why are you typing BASH in all caps](#why-are-you-typing-bash-in-all-caps)?
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- [You are saying you are portable, but why won't b3bp code run in dash / busybox / posh / ksh / mksh / zsh](#you-are-saying-you-are-portable-but-why-wont-b3bp-code-run-in-dash--busybox--posh--ksh--mksh--zsh)?
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- [How do I do Operating System detection](#how-do-i-do-operating-system-detection)?
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- [How do I access a potentially unset (environment) variable](#how-do-i-access-a-potentially-unset-environment-variable)?
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- [How can I detect or trap CTRL-C and other signals](#how-can-i-detect-or-trap-ctrl-c-and-other-signals)?
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- [How can I get the PID of my running script](how-can-i-get-the-pid-of-my-running-script)?
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<!--more-->
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# Frequently Asked Questions
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## What is a CLI?
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A "CLI" is a [command-line interface](https://en.wikipedia.org/wiki/Command-line_interface).
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## How do I incorporate BASH3 Boilerplate into my own project?
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You can incorporate BASH3 Boilerplate into your project in one of two ways:
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1. Copy the desired portions of [`main.sh`](http://bash3boilerplate.sh/main.sh) into your own script.
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1. Download [`main.sh`](http://bash3boilerplate.sh/main.sh) and start pressing the delete-key to remove unwanted things
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Once the `main.sh` has been tailor-made for your project, you can either append your own script in the same file, or source it in the following ways:
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1. Copy [`main.sh`](http://bash3boilerplate.sh/main.sh) into the same directory as your script and then edit and embed it into your script using Bash's `source` include feature, e.g.:
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```bash
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#!/usr/bin/env bash
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source main.sh
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```
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1. Source [`main.sh`](http://bash3boilerplate.sh/main.sh) in your script or at the command line:
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```bash
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#!/usr/bin/env bash
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source main.sh
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```
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## How do I add a command-line flag?
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1. Copy the line from the `main.sh` [read block](https://github.com/kvz/bash3boilerplate/blob/v2.1.0/main.sh#L109-L115) that most resembles the desired behavior and paste the line into the same block.
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1. Edit the single-character (e.g., `-d`) and, if present, the multi-character (e.g., `--debug`) versions of the flag in the copied line.
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1. Omit the `[arg]` text in the copied line, if the desired flag takes no arguments.
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1. Omit or edit the text after `Default=` to set or not set default values, respectively.
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1. Omit the `Required.` text, if the flag is optional.
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## How do I access the value of a command-line argument?
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To find out the value of an argument, append the corresponding single-character flag to the text `$arg_`. For example, if the [read block]
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contains the line
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```bash
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-t --temp [arg] Location of tempfile. Default="/tmp/bar"
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```
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then you can evaluate the corresponding argument and assign it to a variable as follows:
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```bash
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__temp_file_name="${arg_t}"
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```
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## What is a magic variable?
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The [magic variables](https://github.com/kvz/bash3boilerplate/blob/v2.1.0/main.sh#L26-L28) in `main.sh` are special in that they have a different value, depending on your environment. You can use `${__file}` to get a reference to your current script, and `${__dir}` to get a reference to the directory it lives in. This is not to be confused with the location of the calling script that might be sourcing the `${__file}`, which is accessible via `${0}`, or the current directory of the administrator running the script, accessible via `$(pwd)`.
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## How do I submit an issue report?
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Please visit our [Issues](https://github.com/kvz/bash3boilerplate/issues) page.
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## How can I contribute to this project?
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Please fork this repository. After that, create a branch containing your suggested changes and submit a pull request based on the main branch
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of <https://github.com/kvz/bash3boilerplate/>. We are always more than happy to accept your contributions!
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## Why are you typing BASH in all caps?
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As an acronym, Bash stands for Bourne-again shell, and is usually written with one uppercase.
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This project's name, however, is "BASH3 Boilerplate". It is a reference to
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"[HTML5 Boilerplate](https://html5boilerplate.com/)", which was founded to serve a similar purpose,
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only for crafting webpages.
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Somewhat inconsistent – but true to Unix ancestry – the abbreviation for our project is "b3bp".
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## You are saying you are portable, but why won't b3bp code run in dash / busybox / posh / ksh / mksh / zsh?
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When we say _portable_, we mean across Bash versions. Bash is widespread and most systems
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offer at least version 3 of it. Make sure you have that available and b3bp will work for you.
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We run automated tests to make sure that it will. Here is some proof for the following platforms:
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- [Linux](https://travis-ci.org/kvz/bash3boilerplate/jobs/109804166#L91-L94) `GNU bash, version 4.2.25(1)-release (x86_64-pc-linux-gnu)`
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- [OSX](https://travis-ci.org/kvz/bash3boilerplate/jobs/109804167#L2453-L2455) `GNU bash, version 3.2.51(1)-release (x86_64-apple-darwin13)`
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This portability, however, does not mean that we try to be compatible with
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KornShell, Zsh, posh, yash, dash, or other shells. We allow syntax that would explode if
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you pasted it in anything but Bash 3 and up.
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## How do I do Operating System detection?
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We used to offer a magic `__os` variable, but we quickly [discovered](https://github.com/kvz/bash3boilerplate/issues/38) that it would be hard
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to create a satisfactory abstraction that is not only correct, but also covers enough use-cases,
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while still having a relatively small footprint in `main.sh`.
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For simple OS detection, we recommend using the `${OSTYPE}` variable available in Bash as
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is demoed in [this stackoverflow post](http://stackoverflow.com/a/8597411/151666):
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```bash
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if [[ "${OSTYPE}" = "linux-gnu" ]]; then
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echo "GNU Linux"
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elif [[ "${OSTYPE}" = "darwin"* ]]; then
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echo "Mac OSX"
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elif [[ "${OSTYPE}" = "cygwin" ]]; then
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echo "POSIX compatibility layer and Linux environment emulation for Windows"
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elif [[ "${OSTYPE}" = "msys" ]]; then
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echo "Lightweight shell and GNU utilities compiled for Windows (part of MinGW)"
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elif [[ "${OSTYPE}" = "win32" ]]; then
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echo "I'm not sure this can happen."
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elif [[ "${OSTYPE}" = "freebsd"* ]]; then
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echo "..."
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else
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echo "Unknown."
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fi
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```
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## How do I access a potentially unset (environment) variable?
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The set -o nounset line in `main.sh` causes error termination when an unset environment variables is detected as unbound. There are multiple ways to avoid this.
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Some code to illustrate:
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```bash
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# method 1
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echo ${NAME1:-Damian} # echos Damian, $NAME1 is still unset
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# method 2
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echo ${NAME2:=Damian} # echos Damian, $NAME2 is set to Damian
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# method 3
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NAME3=${NAME3:-Damian}; echo ${NAME3} # echos Damian, $NAME3 is set to Damian
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```
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This subject is briefly touched on as well in the [Safety and Portability section under point 5](README.md#safety-and-portability). b3bp currently uses [method 1](https://github.com/kvz/bash3boilerplate/blob/v2.1.0/main.sh#L252) when we want to access a variable that could be undeclared, and [method 3](https://github.com/kvz/bash3boilerplate/blob/v2.1.0/main.sh#L31) when we also want to set a default to an undeclared variable, because we feel it is more readable than method 2. We feel `:=` is easily overlooked, and not very beginner friendly. Method 3 seems more explicit in that regard in our humble opinion.
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## How can I detect or trap Ctrl-C and other signals?
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You can trap [Unix signals](https://en.wikipedia.org/wiki/Unix_signal) like [Ctrl-C](https://en.wikipedia.org/wiki/Control-C) with code similar to:
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```bash
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# trap ctrl-c and call ctrl_c()
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trap ctrl_c INT
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function ctrl_c() {
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echo "** Trapped CTRL-C"
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}
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```
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See http://mywiki.wooledge.org/SignalTrap for a list of signals, examples, and an in depth discussion.
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## How can I get the PID of my running script?
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The PID of a running script is contained in the `${$}` variable. This is _not_ the pid of any subshells. With Bash 4 you can get the PID of your subshell with `${BASHPID}`. For a comprehensive list of Bash built in variables see, e.g., http://www.tldp.org/LDP/abs/html/internalvariables.html
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