`

Listing 2-36

Printing line ranges in a file

When you pass sed the -i argument, it will make the changes to the file

itself rather than create a modified copy (Listing 2-37).

sed -i '1d' log.txt

Listing 2-37

Making changes to the original file

This rich utility can do a whole lot more. Use the man sed command to find

additional ways to use sed.

Job Control

As you become proficient in bash, you’ll start to build complex scripts that

take an hour to complete or must run continuously. Not all scripts need to execute

in the foreground, blocking execution of other things. Instead, you may want to

run certain scripts as background jobs, either because they take a while to

complete or because their runtime output isn’t interesting and you care only about

the end result.

Commands that you run in a terminal occupy that terminal until the command

is finished. These commands are considered foreground jobs. In Chapter 1, we

used the ampersand character (&) to send a command to the background. This

command then becomes a background job that allows us to unblock the execution

of other commands.

Managing Background and Foreground Jobs

To practice working with foreground and background jobs, let’s run a

command directly in the terminal and send it to the background:

$ sleep 100 &

Notice that we can continue working on the terminal while this sleep

command runs for 100 seconds. You can verify the spawned process is running by

using the ps command:

$ ps -ef | grep sleep

user 1827 1752 cons0 19:02:29 /usr/bin/sleep

Now that this job is in the background, we can use the jobs command to see

what jobs are currently running (Listing 2-38).

$ jobs

[1]+ Running sleep 100 &

Listing 2-38

Listing jobs

The output shows that the sleep command is in Running state and that its

job ID is 1.

Black Hat Bash (Early Access) © 2023 by Dolev Farhi and Nick Aleks