Shell Scripting is a way to take shell commands that you could use from a normal command line and string them together allowing it to be run as a program allowing for automating repetitive tasks. Bash scripting is just one shell scripting language. Be aware that shell scripting is not the same as traditional programming languages, rather it’s one type of language called scripting languages. Scripting unlike traditional programming doesn’t need to be built/compiled after being created. Scripts are also typically less complex than full-blown software applications. In this blog post, we will touch on loops in bash scripting and move on to how bash continue statements can be used in loops.
What Is A Bash Loop?
In programming a loop is used to execute a specific code block repeatedly. During loop execution, the loop iterates over the information passed to it. The same goes for bash loops which allow for specific code to loop through to perform specified tasks.
The Bash Continue Statement
The bash continue statement is used within loops to skip the current iteration of the loop before the loop starts over again. It should be noted that the bash continue statement can only be used in for, while, and until loops.
Examples
The following example scripts include a mix of loops but all include the continue statement.
Wait For File To Exist
#!/bin/bash
until [ -f file.txt ]
do
continue
done
echo "File found!"
This example waits till a file with the file name of file.txt is created and prints out a message.
Wait Until A Set Time Is Reached
#!/bin/bash
target_time=$(date -d "12:00" +%s)
until [ $(date +%s) -ge "$target_time" ]
do
sleep 1
continue
done
echo "Target time reached!"
This example waits for noon and then prints out a message.
Wait For The Ping To Fail
#!/bin/bash
while true; do
if ping -c 1 google.com > /dev/null
then
continue
else
echo "Ping Failed check internet connectivity"
fi
sleep 10
done
This example is a ping check that when fails prints out a message.
Did you notice this is also used nested loop? Although the original loop is a while loop there is a nested if loop inside it. From this point onward the rest of the examples have at least one nested loop.
List Files In the Correct Directory
#!/bin/bash
for f in $(ls); do
if [ ! -f $f ]; then
continue
fi
echo "File located: $f"
done
This example uses the ls command in the current directory and using the test command prints out the names of files.
Disk Usage Warning
#!/bin/bash
for dir in /home/*
do
if [ ! -d "$dir" ]
then
continue
fi
disk_usage=$(du -sh $dir | cut -f1)
if [ ${disk_usage%G} -gt 80 ]
then
echo "Disk usage for $dir is high: $disk_usage"
fi
done
This example waits for disk usage to reach 80% and then prints out a warning.
Conclusion
When bash scripting loops are invaluable for automating repetitive tasks. The bash continue statement can only be used in loops. The continue statement skips the current iteration of the loop. The next iteration of the loop will then kick off and run through again testing the specified conditions.
If you creating a bash script with loops the continue statement may be just what you need to allow for better loop control.
Additional Links
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Embracing a lifelong passion for technology since childhood, CJ delved into the intricate workings of systems, captivated by the desire to understand the unknown. This innate curiosity led to his discovery of Linux, a revelation that resonated deeply. With more than 7 years of on the job experience, he’s honed his technical skills as a Geek and Senior Linux Systems Administrator.
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