Scripting : useful content commands

This week, we will review the commands which handle content.

They are useful when you need to display the content of files or variables easily in a Terminal.

Command	Description
echo	Displays a simple text string on the screen
printf	Displays text with precise formatting
cat	Displays the entire content of a file
head	Displays the first lines of a file
tail	Displays the last lines of a file
less	Allows interactive viewing of a file’s content
more	Displays the content of a file page by page
zcat	Displays the content of a gzip-compressed file

echo

echo is a basic command to display a text or a variable in the Terminal.

For instance, if you would like to display the current user type:

echo $USER

You can also display any other message to the Terminal and in addition redirect the result to a file like below:

echo "Welcome to Haiku!" >welcome.txt

This command is not a well known command - compared to echo - but when you need to display a message in a specific format, this is the one to use:)

In case you want to display a welcome message to the current user, in a Terminal type:

printf "Hello %s! \n" $USER

The "%s" will indicate to display a string variable which is contained in the "$USER" variable.

You can also decide to display information like Name and Age with a specific width and align to the left:

This commands stands for "concatenate".

It's needed when you want to display the content of a file like below:

cat /boot/home/config/settings/boot/UserSetupEnvironment.sample

In case the content of the file is higher than the height of the Terminal, you can use the "more" command at the end:

cat /boot/home/config/settings/boot/UserSetupEnvironment.sample | more

In that case, the file will be displayed on a page by page basis.

You can also decide to use the cat command to concatenate 2 files into one:

cat welcome.txt welcome.txt >new_welcome.txt

In the above example, the content of the file "welcome.txt" is displayed twice and the result is put inside the new file "new_welcome.txt".

You can also use the "cat" command with the "-n" option to display the line numbers:

cat -n new_welcome.txt

This is a nice and simple command to display the first lines of a file.

If you need to display the first 5 lines of the system log file, type in a Terminal:

head -n 5 /var/log/syslog

The tail command is the opposite of the head one: it will display the last 10 lines of a file.

In case you need to display the last lines of the system log file, type:

tail -f /var/log/syslog

The "-f" option - which means follow - will allow to continue the display when new lines are created like below:

A really useful command:)

The less command allows interactive viewing of a file’s content.

You can move forward or backward in the file and search for content with the "/" character.

The percentage of the content of the file is displayed at the bottom line:

And when you reach the end of the file, the below status is displayed:

In case you search for the word "file", type "/file", and the results will be highlighted as below:

You can quit the display with the "q" character.

more is supposed to be a page by page display like less, but the file will be loaded completely (where less will load the file on the fly).

The display of a page will be like below:

Not sure if both less and more are different, because when you check for the help on more:

more --help

It indicates "less" commands:

In case you would like to read the content of a gzip file, the zcat command is quite useful.

Let's archive the previous "welcome.txt" file into gzip format:

gzip welcome.txt

Now let's verify if the zcat can read the content of this archived message:

zcat welcome.txt.gz

Yes!

It's working as expected.

Any other content command you would like to share?

If so, you can put a comment below.