Standard functions library for bash shell
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README.md

Standard functions library for bash

Even though no POSIX-compatible shell is likely to win any performance awards, the capabilities of modern shells - especailly bash-4 and above - now allow significant power and flexibility. However, many shell-scripts remain afterthoughts, quickly thrown together without any consideration of- or adherence to- any particular standards. Due to the lack of any widely adopted standard functions, many scripts either lack even the most basic of error- handling techniques, or spend much time re-implmenting boiler-plate code. This library is intended to live in /usr/local/lib, and either be included in any scripts which wish to make use of the standardised functions - or even sourced from ~/.bashrc in order to speed individual script execution.

Orientation

stdlib.sh requires at least bash-2.02 (for [[ ... ]] in-process conditional evaluation), and several functions use the =~ regular-expression match operator introduced in bash-3. If bash-4 features such as associative arrays are available, then the environment variable STDLIB_HAVE_BASH_4 is set on load - see below.

Invoking a script which employs stdlib.sh with the DEBUG environment variable set may produce additional diagnostic output. Explicitly setting DEBUG=2 will additionally output stdlib.sh internal diagnostic information.

A template.sh file is now provided with all of the necessary components needed to use stdlib.shalready included, making getting started much simpler and quicker. The suggested configuration is to edit with vi or vim with set modeline in ~/.vimrc, to allow for code-folding and so easier editing.

Coding Standards

All scripts should, following the interpreter line at the very top of the file, include the stdlib.sh loader code from the top of /usr/local/lib/stdlib.sh. stdlib will only execute itself if its functions aren't already initialised. On load, stdlib.sh invokes set -u which causes bash to abort execution if a run-time attempt is made to address an unbound variable. Because of this, any third-party scripts should be sourced before stdlib.sh is loaded - however, since the unbound-variable checking is perfomed at run-time only, any functions in sourced scripts may still trigger an unbound variable error on execution.

Only global variables (in ALLCAPS, by convention) should be defined outside of any function, and should follow the stdlib.sh inclusion code. The main-loop of the script's function should be contained within a main() function, which should in turn call other functions as appropriate. All other variables should be declared 'local' within the function in which they are used. Other useful declarations are:

  • local -i : Define an integer variable, which accepts only numbers, defaults to value 0, and will never return a value of true in response to test -z;

  • local -u : Define an upper-case variable, where any assigned value is automatically converted to upper-case;

  • local -l : Define a lower-case variable, where any assigned value is automatically converted to lower-case;

  • local -a : Define an array variable;

  • local -A : Define an associative array;

For top-level global values outside of functions, declare can be used in place of local. Top-level variables must stil be exported in order to be visible to sub-shells.

stdlib.sh is designed on the principal that successful function execution elicits a return-code of zero, whilst non-zero indicates an error. Calling exit (or die) is generally avoided in functions, leaving the caller to decide on the severity of a failure. Code considered unreachable, if ever executed, should return a canary value of 255. Only values between 0 and 255 are valid return-codes - returning a negative value, sometimes seen in code written by Java programmers particularly, will actually return 256 less the absolute value of the return code.

It is suggested that all variables be enclosed within braces, and also double-quoted unless defined as a numeric value with local -i or declare -i. The exception to this is where a variable is used in place of a command, where braces should be omitted in order to differentiate commands from values.

local string="text"
output "${string:-}"

local -i rc=0
return ${rc}

declare DEBUG_RM="echo rm"
$DEBUG_RM "${files[@]}"

Functions

Function Description
output() An alias for echo, used to indicate user-visible output
respond() An alias for echo, used to indicate response feedback
std::cleanup() Remove any temporary files created by the mktemp functions or added by std::garbagecollect
std::usage-message() Provide custom help-text where ${std_USAGE} is not sufficient
std::usage() Output help text from ${std_USAGE} or std::usage-message()
std::wrap() Format text to wrap to the width of the console at a word-end - N.B. May require 'export COLUMNS'
std::log() Output text to console, file, or syslog
std::colour() Optionally determine intended text colour from string prefix, and return text with ANSI escapes
die() Output text in a standardised format and exit with a failure code
error() Output text in a standardised format
warn() Output text in a standardised format
note() Output text in a standardised format
notice() Output text in a standardised format
info() Output text in a standardised format
debug() Output text in a standardised format
symerror() errno: Provide symbol name (such as 'EERROR') for specified code
errsymbol() errno: Provide code for specified symbol
strerror() errno: Provide description string for most recent or specified code
std::garbagecollect() Add additional files for automatic removal on exit
std::mktemp() OS-neutral standard mktemp(1) replacement, with garbage collection
std::emktemp() Enhanced mktemp(1) replacemnt with improved syntax
std::push() Push() implementation - see Martin Väth's original here
std::readlink() Basic OS-neutral readlink(1) stand-in
std::inherit Document the use of global variables
std::define() Improved HEREDOC support, without the need to invoke cat
std::formatlist() Return an English-formatted list with Oxford comma
std::vcmp() Compare two specified versions, or output a list of versions and succeed if the list was sorted
std::requires() Declare script command requirements/dependencies
std::capture() Capture the output- or error- stream of a command
std::ensure() Exit with a specified error message if a command fails
std::silence() Execute a command and drop all output (e.g. >/dev/null 2>&1)
std::wordsplit() Return each whitespace-separated element from the (quoted) input, without unexpected globbing
std::findfile() Given an application name, file name, and default directory find a likely data file
std::getfilesection() Retrieve a single section from a Windows-style .ini file with square-bracketed section titles
std::parseargs() Allow functions to accept named parameters with only minor code-changes
std::configure() Export variables containing the standard system paths as used by configure scripts
std::http::squash() Map HTTP response codes (100-599) down to shell return codes (0-255) by squashing unused values
std::http::expand() Map shell return codes (0-255) back up to HTTP response codes (100-599)

Configuration Files

The example file stdlib-colour.map may be copied to /etc/stdlib/colour.map or /etc/stdlib.colour.map (or similar locations beneath /usr/local/etc, or even ~/.stdlib/colour.map or ~/.stdlib.colour.map - see std::findfile() for details of how this flexibility can easily be achieved in your own scripts), or an alternate location may be specified by setting the environment variable STDLIB_COLOUR_MAP to the full path to the map file. stdlib-colour.map documents the available colour options.

The colour mappings from stdlib-colour.map are used when stdlib.sh is sourced with the environment variable STDLIB_WANT_COLOUR set - for backwards- compatibility, colourised output is disabled by default.