Reading & Editing Files

cat — print file contents

cat (concatenate) prints a file to the terminal.

$ cat notes.txt
Remember to water the plants.

It can print several files in sequence:

$ cat part1.txt part2.txt

Useful flags:

$ cat -n notes.txt
     1  Remember to water the plants.

cat is fine for short files. For anything longer, use less.

Graphical alternative: any text editor or file viewer opens a file with a double-click.

less — page through files

less displays a file one screen at a time. It does not flood the terminal the way cat does with long files.

$ less /var/log/syslog

(On Fedora the log lives in the journal instead — journalctl in Chapter 14 reads it, and sudo dnf install rsyslog adds the file. On Ubuntu the file is there from the start.)

While in less:

less also reads from a pipe, which is the most common way to use it. (A pipe, |, sends one command’s output into the next command — it gets a full treatment in Chapter 13.)

$ ps aux | less

head — show the start

head shows the first ten lines by default.

$ head /var/log/syslog

Use -n for a different count:

$ head -n 3 notes.txt
line1
line2
line3

head -c limits by bytes instead of lines:

$ head -c 100 file.bin > first100.bin

tail — show the end

tail shows the last ten lines by default.

$ tail /var/log/syslog

Use -n for a different count:

$ tail -n 5 notes.txt

The -f flag (follow) keeps the file open and prints new lines as they are appended. This is invaluable for watching logs live:

$ tail -f /var/log/syslog

Press Ctrl+C to stop following.

Graphical alternative: GNOME Logs or your file viewer can show the same information, but tail -f is often faster.

nano — the beginner-friendly editor

nano is a small text editor that runs in the terminal. It shows its key bindings at the bottom of the screen, which makes it ideal for newcomers.

$ nano notes.txt

Key bindings (the ^ means the Ctrl key):

The basic workflow: type nano file, edit, press Ctrl+O then Enter to save, then Ctrl+X to exit.

Default status: nano is preinstalled on Ubuntu desktops. On Fedora and Arch it usually needs installing first: sudo dnf install nano / sudo pacman -S nano. If nano is missing, vim-tiny or vi are present on most systems as a fallback.

echo — print text

echo prints its arguments to the terminal.

$ echo hello
hello

echo is mostly used in scripts and with shell features, for example to write to a file:

$ echo "Hello world" > greeting.txt
$ cat greeting.txt
Hello world

$ echo -n "no newline here"

echo with -e interprets escape sequences like \t (tab):

$ echo -e "col1\tcol2"
col1	col2