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Helper functions commonly used when writing shell (for instance, Bash) scripts.
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README.md
bash-common-helpers.sh bash_ini_parser now contains BSD-3-Clause license Apr 5, 2015

README.md

Bash Common Helpers

This repository contains Bash utility functions I use in my Bash (and Zsh) scripts regularly. These functions are provided through a small library called bash-common-helpers. The library saves the trouble to redefine commonly used helper functions every time you write a shell script – be it a simple, quickly written script or a more elaborate utility. Especially in the first case, the library may save a great part of the development time.

Overview

The library currently provides the following helper functions:

Script Initialization

  • cmn_init – supposed to be called at the beginning of every script. Makes scripts more robust by setting various shell options.
  • cmn_assert_running_as_root – makes sure that the script is run as root.

Printing to the Screen

  • cmn_echo_info – prints informative message in green letters.
  • cmn_echo_important – prints message of higher importance in yellow letters.
  • cmn_echo_warn – prints warning in red letters.

Error Handling

  • cmn_die – writes message in red letters to standard error and exits.

Availability of Commands and Files

  • cmn_assert_command_is_available – makes sure that the given command is available.
  • cmn_assert_file_exists – makes sure that the given regular file exists.
  • cmn_assert_file_does_not_exist – makes sure that the given file does not exist.

User Interaction

  • cmn_ask_to_continue – asks the user whether to continue or not.
  • cmn_ask_for_password – prompts the user for a password. Instead of echoing the entered characters, asterisks (*) are printed.
  • cmn_ask_for_password_twice – asks the user for her password twice and checks if both inputs match.

File Utilities

  • cmn_replace_in_files – replaces given string in files. The function uses perl to provide a robust implementation.

Parsing INI Files

  • cmn_parse_ini_file – parses INI file using Ruediger Meier's "simple INI file parser".
  • cmn_assert_ini_variables_exist – makes sure that the given INI variables exist and provides feedback to the user if not.

Note prefix cmn_ which is supposed to avoid clashes with the names of functions defined in your script or in any other included script.

Installation

In a nutshell: just make a clone of this repository on your harddisk and load the library by sourcing it.

For instance, go to directory ~/local/lib and clone the repository there. In this case, the library files will end up in directory ~/local/lib/bash-common-helpers.

Now, you have to source the main library file in your scripts. This basically reads and executes the commands in the library files in your script's context and thus makes all the library helper functions available to your script.

Using an Environment Variable

I prefer to set an environment variable that refers to the library path and to use that variable to source the library file in my scripts. This way, when I move the library on my hard disk, I do not have to adapt all my scripts but the environment variable only.

To set the environment variable, add the following line to your .bashrc, .zshrc, or whatever rcfile file you are using:

export BASH_COMMON_HELPERS_LIB="~/local/lib/bash-common-helpers/bash-common-helpers.sh"

Then, use the following header in your scripts:

#!/bin/bash

# BEGIN: Read functions from bash-common-helpers library.
if [[ -z "${BASH_COMMON_HELPERS_LIB}" ]]; then
  echo "Required environment variable is not set: BASH_COMMON_HELPERS_LIB"
  exit 1
fi
if [[ ! -f "${BASH_COMMON_HELPERS_LIB}" ]]; then
  echo "Required file does not exist: ${BASH_COMMON_HELPERS_LIB}"
  exit 2
fi
source "${BASH_COMMON_HELPERS_LIB}"
cmn_init || exit 3
# END: Read functions from bash-common-helpers library.

# Your actual script starts here.
cmn_echo_info "Could source lib file successfully."

Using Path to Library Directly

Of course, you can omit the above environment variable and refer to the library directly:

#!/bin/bash

# BEGIN: Read functions from bash-common-helpers library.
BASH_COMMON_HELPERS_LIB="~/local/lib/bash-common-helpers/bash-common-helpers.sh"
if [[ ! -f "${BASH_COMMON_HELPERS_LIB}" ]]; then
  echo "Required file does not exist: ${BASH_COMMON_HELPERS_LIB}"
  exit 1
fi
source "${BASH_COMMON_HELPERS_LIB}"
cmn_init || exit 2
# END: Read functions from bash-common-helpers library.

# Your actual script starts here.
cmn_echo_info "Could source lib file successfully."

Documentation

For the documentation of the library, please refer to the source code: each function in the library has an explaining comment which is written above it. That comment contains the purpose of the function as well as an example which shows how to call the function.

Credits

Many functions have their roots in various web pages, blog posts, and lastly in answers provided by the phenomenal Stack Exchange Q&A communities. Whenever possible, I refer to the most relevant source in the documentation of the functions.

Function cmn_parse_ini_file uses Ruediger Meier's "simple INI file parser" which is available at GitHub. Actually, the library includes that parser for reasons of convenience.

Last but not least, the library contains valuable knowledge and experience of coworkers who showed my one or two tricks.

License

Released under the MIT License (MIT) – see file LICENSE in this software's repository.

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