(RHCSA) Create Simple Shell Scripts

This is part of the independent and unofficial RHCSA Exam Study Guide series providing free 🤑 resources to prepare for the exam.

This post covers the objectives under the section:

“CREATE SIMPLE SHELL SCRIPTS”

It contains two main parts:

• Resources: with links to learn and practice for each objective.
• Cheatsheet: containing some examples of commands and actions performed in each objective (when applied).

📚 Resources:

• 📌 What is Bash Scripting?

• 📌 Bash Scripting Tutorial - 1. What is a Bash Script?

CONDITIONALLY EXECUTE CODE (USE OF: IF, TEST, [], ETC.)

• 📌 RHCSA v8 Practice Session: Conditionally execute code (use of: if, test, [], etc.)

• 📌 Bash Scripting Tutorial - 5. If Statements

USE LOOPING CONSTRUCTS (FOR, ETC.) TO PROCESS FILE, COMMAND LINE INPUT

• 📌 RHCSA v8 Practice Session: Use looping constructs (for, etc.) to process file, command line input

• 📌 Bash Scripting Tutorial - 6. Loops

PROCESS SCRIPT INPUTS ($1, $2, ETC.)

• 📌 RHCSA v8 Practice Session: Process script inputs ($1, $2, etc.)

• 📌 Bash Scripting Tutorial - 2. Variables

• 📌 Bash Scripting Tutorial - 3. User Input

• 📌 Bash Scripting Tutorial - 7. Functions

PROCESSING OUTPUT OF SHELL COMMANDS WITHIN A SCRIPT

• 📌 RHCSA v8 Practice Session: Processing output of shell commands within a script

• 📌 Command substitution

• 📌 3.5.4 Command Substitution

PROCESSING SHELL COMMAND EXIT CODES

• 📌 RHCSA v8 Practice Session: Processing shell command exit codes

• 📌 Bash Exit Command and Exit Codes

• 📌 Understanding Exit Codes and Using them in Bash scripts

📑 Cheatsheet:

CONDITIONALLY EXECUTE CODE

#!/bin/bash

if [ "$(uname)" == "Linux" ]
then 
    echo "OK"
else 
    echo "nah"
fi

#!/bin/bash

if test "$(uname)" == "Linux"
then 
    echo "OK"
else 
    echo "nah"
fi

USE LOOPING CONSTRUCTS (FOR, ETC.) TO PROCESS FILE, COMMAND LINE INPUT

#!/bin/bash

ls "$1" > files.tmp

while read filename
do
    echo "$(basename $filename | cut -d '.' -f 1)"
done < files.tmp

rm files.tmp

PROCESS SCRIPT INPUTS ($1,$2, ETC.)

#!/bin/bash

COUNTER=1

if [ "$#" -gt 0 ]
then
    for i in "$@"
    do
        echo "Argument $COUNTER is $i"
        ((COUNTER++))
    done
else
    echo "No arguments passed to the script."
fi

PROCESSING OUTPUT OF SHELL COMMANDS WITHIN A SCRIPT

#!/bin/bash

for i in $(find . -maxdepth 1 -type f)
do      
    echo "filename is: $(echo $i | cut -c 3-)"
done    

PROCESSING SHELL COMMAND EXIT CODES

#!/bin/bash

date | grep Sun

if [[ $? -eq 0 ]]
then
    echo "Go to the beach, it's sunday" 
    exit 0
else
    echo "Please get back to work"
    exit 1
fi

Next:

(RHCSA) Operate Running Systems

…or back to Red Hat Certified System Administrator (RHCSA) Exam Study Guide

Useful links & references:

• Red Hat Enterprise Linux Documentation

• Enable Sysadmin (a blog from Red Hat)

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