Terminal File Viewing Commands - Computer Science Hub

Terminal is an application that runs commands given by user, actually there is a special program inside Terminal called Shell – which reads in commands and execute them on Mac OS operating system.Terminal’s only job is to open windows and manage shells, while shells actually do real work of Command Execution. You can enter commands in Terminal and then Shell Program running inside terminal will execute those commands.

Commands are a kind of way to interact with Operating System and File System. These can be used for creating files/directories or checking status of processes being run by the Operating System. That’s why these can be really useful, moreover terminal commands can be used for building programming projects as well. Like you can build a Django Framework based website just from Terminal. Moreover, Terminal can be used for compiling/executing multiple files in a large Software Engineering Project. That’s why every beginner in Software Engineering should be aware about What is Terminal, How does it works and what are commands which can be used in it? Also if in case you already don’t know what is terminal then check out this article – What is Terminal in MAC OS?.
Anyway let’s get into what File Viewing Operations can be used in Mac Terminal.

File Viewing Operations Commands

Below is a table containing commands which can be used for viewing files in the file system in Mac.

File Viewing Commands	Description
cat	For viewing entire content in a file
less	For viewing text files one page at a time
head	For viewing just few first lines of a text file
tail	For viewing just last lines of a text file
nl	For viewing text files with their lines numbered

cat – File Viewing Command

For viewing entire content in a file.
cat command in general can be written as cat [options] [files]
For example – In the below picture, cat index.html command shows all of content in the HTML File.

Options for cat command

Options for cat command	Description
cat -v filename	For printing out any nonpriniting character
cat -t filename	Kind of similar to -v option, but can also print tab
cat -e filename	Similar to -v option, but also print newlines as $
cat -n filename	Prepend line number to every line
cat -b filename	Prepend line numbers to nonblank lines
cat -s filename	Squeeze each sequence of blank lines into a single blank line

cat -v filename example

cat -t filename example

cat -e filename example

cat -n filename example

cat -b filename example

cat -s filename example

less – File Viewing Command

For viewing text files one page at a time and also can be used for editing the file.
less command in general can be written as less [option][filename]
For example – In the below picture, less index.html command opens up file in an editable mode.

Options for less command

Options for less command	Description
less -c filename	Clears the screen before displaying the content in file
less -m filename	Displays the percentage of the file displayed so far in Terminal window
less -N filename	Displays line numbers

head – File Viewing Command

For viewing just few first lines of a text file.
head command in general can be written as head [option][filename]
For example – In the below picture, head index.html just shows some few first lines in index.html file.

Options for head command

Options for head command	Description
head -N filename	Print first N lines in file
head -c N filename	Print first N bytes of file

head -N filename command example

head -c N filename command example

tail – File Viewing Command

For viewing just last lines of a text file.
tail command in general can be written as tail [options][filename]
For example – In the below picture, tail index.html command shows some content of index.html file from end of file.

Options for tail command

Options for tail command	Description
tail -N filename	Prints last N lines of a file
tail -c N filename	Prints out last N bytes of a file

tail -N filename command example

tail -c N filename command example

nl – File Viewing Command

For viewing text files with their lines numbered.
nl command in general can be written as nl [options][filename]
For example – In the below picture, nl index.html command prints out content of index.html file with lines being numbered.

Options for nl command

Options for nl command	Description
nl -v N filename	Prints out lines of a file being numbered, starting with integer N
nl -i N filename	Prints out lines of a file being numbered, incrementing number of line by N each time while moving from one line to next line
nl -s S filename	Prints out lines of a file being numbered, but inserter S string inbetween number and line