Shell test conditions and exit codes

Tutorials – Shell Scripting

Article from Issue 222/2019
Author(s):

The Bash shell uses different criteria to make decisions. Learn how to teach your shell scripts to make the right choice.

In the previous installment of this series [1], I  described how to add different possible courses of action to a script, so that the script can choose by itself which action to execute while running. In this issue, I will explain how to teach a script to choose which of the available actions to execute.

Often, the real decision-making challenge lies not in figuring out whether your shell script needs a while loop or some nested if statements but rather in determining the conditions that will tell your script when it should stop that loop or which branch of that "if" statement to execute. The main Bash tools for this purpose are a big set of test operators (see the descriptions online [2] [3] [4]) and their corresponding syntax, which can evaluate whether some condition is true or false. By contrast, exit status codes [5] are the traces that built-in commands, or whole scripts, leave behind to communicate their achievements.

In this article you will learn through examples and working code:

[...]

Use Express-Checkout link below to read the full article (PDF).

Buy this article as PDF

Express-Checkout as PDF
Price $2.95
(incl. VAT)

Buy Linux Magazine

SINGLE ISSUES
Print Issues
Digital Issues
 
SUBSCRIPTIONS
Print Subs
Digisubs
 
TABLET & SMARTPHONE APPS
Get it on Google Play

US / Canada

Get it on Google Play

UK / Australia

Related content

  • Bash scripting

    A few scripting tricks will help you save time by automating common tasks.

    more »
  • Batsh

    Batsh kills two birds with one stone: Programs written in this language can be compiled both as Linux Bash scripts and Windows batch files.

    more »
  • SHC: Bash Script Compiler

    The Bash Shell Script Compiler converts shell scripts directly into binaries. Compiling your scripts provides protection against accidental changes, but you will have to contend with some quirks.

    more »
  • PHP-CLI

    PHP is not just for websites. Command-line PHP scripting has been around for more than 10 years, which makes the language and its comprehensive libraries eminently suitable for the toolbox of any administrator who manages web servers.

    more »
  • Bash 4

    Despite the Bourne-again shell's biblical age and high level of maturity, developers continue to work on it. We take a look at the latest Bash release.

    more »
comments powered by Disqus

Visit Our Shop

Trial Subscription

Digital Subscription

Subscribe

Direct Download

Read full article as PDF:

Price $2.95

GPU Computing

News

Tag Cloud

Administration Community Desktop Events Hardware Linux Linux Pro Magazine Mobile Programming Software Ubuntu Web Development Windows free software open source