Section 1.1: The wc Command

The wc command is used to count lines, words, or bytes within a file. For example, to count the lines in a file named test.txt, you would execute:

wc -l test.txt

To count the words in the same file, use:

wc -w test.txt

For byte count, the command is:

wc -c test.txt

Additionally, the -m flag can be used to get an accurate byte count.

Section 1.2: Opening Files and Directories

The open command allows users to access files, directories, and applications. To open a specific file, simply run:

open filename

If you wish to open the current directory, use:

open .

Section 1.3: Changing Passwords

The passwd command is utilized for modifying a user’s password. When executed, it prompts for the current password and the new password you wish to set. Superusers can also change another user's password using:

passwd username

Section 1.4: Modifying File Permissions with chmod

The chmod command enables users to alter file permissions. To change permissions, the command format is as follows:

• a for all
• u for user
• g for group
• o for others

You can add permissions using + or remove them using -. Permission types include:

• r — read
• w — write
• x — execute

For instance, to grant read permission to all users for a file named filename, use:

chmod a+r filename

To revoke read permission from both the group and others, the command would be:

chmod og-r filename

Permissions can also be set numerically. Each number corresponds to permission levels:

• 0 — no permissions
• 1 — execute
• 2 — write
• 3 — write and execute
• 4 — read
• 5 — read and execute
• 6 — read and write
• 7 — read, write, and execute

To set full permissions for everyone, you would run:

chmod 777 filename

Section 1.5: Changing File Ownership

To change the owner of a file or directory, the chown command is utilized. The syntax is:

chown newuser filename

For example, to transfer ownership of test.txt to a user named user, you would execute:

chown user test.txt

To change ownership recursively, add the -R flag:

chown -R newuser directoryname

You can also assign ownership to a group using:

chown :groupname filename

For instance, to change the owner of test.txt to bob in the users group, use:

chown bob:users test.txt

Section 1.6: Modifying Groups with chgrp

The chgrp command allows you to change the group ownership of a file. The command format is:

chgrp newgroup filename