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Shell scripting is the easiest form of programming you can learn/do in Linux. More so, it is a required skill for system administration for automating tasks, developing new simple utilities/tools just to mention but a few.
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In this article, we will share 10 useful and practical tips for writing effective and reliable bash scripts and they include:
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1. Always Use Comments in Scripts
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This is a recommended practice which is not only applied to shell scripting but all other kinds of programming. Writing comments in a script helps you or some else going through your script understand what the different parts of the script do.
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For starters, comments are defined using the # sign.
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#TecMint is the best site for all kind of Linux articlesrn
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2. Make a Script exit When Fails
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Sometimes bash may continue to execute a script even when a certain command fails, thus affecting the rest of the script (may eventually result in logical errors). Use the line below to exit a script when a command fails:
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#let script exit if a command failsrnset -o errexit rnORrnset -ern
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3. Make a Script exit When Bash Uses Undeclared Variable
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Bash may also try to use an undeclared script which could cause a logical error. Therefore use the following line to instruct bash to exit a script when it attempts to use an undeclared variable:
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#let script exit if an unsed variable is usedrnset -o nounsetrnORrnset -urn
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4. Use Double Quotes to Reference Variables
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Using double quotes while referencing (using a value of a variable) helps to prevent word splitting (regarding whitespace) and unnecessary globbing (recognizing and expanding wildcards).
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Check out the example below:
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#!/bin/bashrn#let script exit if a command failsrnset -o errexit rnrn#let script exit if an unsed variable is usedrnset -o nounsetrnrnecho "Names without double quotes" rnechornnames="Tecmint FOSSMint Linusay"rnfor name in $names; dorn echo "$name"rndonernechornrnecho "Names with double quotes" rnechornfor name in "$names"; dorn echo "$name"rndonernrnexit 0rn
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Save the file and exit, then run it as follows:
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$ ./names.shrn
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5. Use functions in Scripts
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Except for very small scripts (with a few lines of code), always remember to use functions to modularize your code and make scripts more readable and reusable.
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The syntax for writing functions is as follows:
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function check_root(){rntcommand1; rntcommand2;rn}rnrnORrncheck_root(){rntcommand1; rntcommand2;rn}rn
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For single line code, use termination characters after each command like this:
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check_root(){ command1; command2; }rn
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6. Use = instead of == for String Comparisons
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Note that == is a synonym for =, therefore only use a single = for string comparisons, for instance:
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value1=”tecmint.com”rnvalue2=”fossmint.com”rnif [ "$value1" = "$value2" ]rn
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7. Use $(command) instead of legacy ‘command’ for Substitution
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Command substitution replaces a command with its output. Use $(command) instead of backquotes `command` for command substitution.
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This is recommended even by shellcheck tool (shows warnings and suggestions for shell scripts). For example:
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user=`echo “$UID”`rnuser=$(echo “$UID”)rn
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8. Use Read-only to Declare Static Variables
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A static variable doesn’t change; its value can not be altered once it’s defined in a script:
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readonly passwd_file=”/etc/passwd”rnreadonly group_file=”/etc/group”rn
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9. Use Uppercase Names for ENVIRONMENT Variables and Lowercase for Custom Variables
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All bash environment variables are named with uppercase letters, therefore use lowercase letters to name your custom variables to avoid variable name conflicts:
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#define custom variables using lowercase and use uppercase for env variablesrnnikto_file=”$HOME/Downloads/nikto-master/program/nikto.pl”rnperl “$nikto_file” -h “$1”rn
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10. Always Perform Debugging for Long Scripts
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If you are writing bash scripts with thousands of lines of code, finding errors may become a nightmare. To easily fix things before executing a script, perform some debugging. Master this tip by reading through the guides provided below:
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- How To Enable Shell Script Debugging Mode in Linux
- How to Perform Syntax Checking Debugging Mode in Shell Scripts
- How to Trace Execution of Commands in Shell Script with Shell Tracing
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That’s all! Do you have any other best bash scripting practices to share? If yes, then use the comment form below to do that.
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