File and Folder Management Quiz

### File and Folder Management

• ls command is used to list files and directories. To get a more detailed information, use ls -l.
• touch command is used to create an empty file.
• mkdir dirname is used to create a directory.
• cd dirname is used to change the working directory.
• cd.. is used to navigate one level up in the directory structure.
• cd ../../.. navigates three levels up in the directory structure.
• mkdir -p temp1/temp2/temp3 is used to create a complete directory structure, including intermediate directories.

### File Editing with vi

• vi editor is used to edit files.
• To enter insert mode, press esc followed by i.
• To save and quit the file, press esc followed by :wq!.
• To quit without saving, press esc followed by :q!.
• :%s/current-string/new-string/g is used to replace all instances of a string in a file.
• 4s/linux/windows/g replaces all instances of "linux" to "windows" in the 4th line.
• 2,4s/linux/windows/g replaces all instances of "linux" to "windows" from the 2nd to 4th line.
• 2,$s/linux/windows/g replaces all instances of "linux" to "windows" from the 2nd line to the end of the file.
• :set nu enables line numbers in vi
• :set nonu disables line numbers in vi.
• :line_number moves the cursor to the specified line number.
• dd deletes the current line in vi.

File Copying and Moving

• cp is used to copy files and directories.
• cp file1 file2 copies file1 to file2.
• cp test1 temp1/temp2/temp3/ copies test1 file to the specific directory path.
• cp -r dir1 dir2 copies directory dir1 to dir2, including all subdirectories and files.
• cp test1 file1 test3 temp copies multiple files or directories to a destination directory.
• mv is used to rename or move files and directories.
• mv file1 file2 renames file1 to file2.
• mv file1 dir2/ moves file1 to directory dir2.
• mv file1 file2 file3 dir1 moves multiple files to a directory.

File Permissions and Ownership

• chmod is used to change the permissions of a file or directory.
• chmod 777 filename changes the permissions of the file to read, write, and execute for owner, group, and others.
• chmod -R 777 dir recursively changes the permissions of all files and directories within the specified directory.
• chown newowner filename changes the owner of the file to newowner.
• chown newowner:groupname filename changes the owner and group of the file.

File Size and Disk Usage

• df -h displays the disk usage of the mounted file systems.
• du -sh filename displays the size of a file in human-readable format.
• du -sh * displays the size of all files and directories in the current directory.

Basic Output and Redirection

• echo "hi how r u" prints the string to the terminal.
• echo -e "hi\nhow r u" prints the string with newline character.
• > redirects the output of a command to a file.
• ls -lrt > log redirects the output of ls -lrt command to log file.
• >> appends the output of a command to the end of a file.
• echo "this is linux class" >> log appends the string this is linux class to the log file.

File Counting and Content Manipulation

• wc command is used to count lines, words and characters in a file.
• wc -l log counts the number of lines in the log file.
• wc -w log counts the number of words in the log file.
• wc -c log counts the number of characters in the log file.
• head command is used to display the first n lines of a file.
• head -3 filename displays the first 3 lines of the file.
• head filename displays the first 10 lines of the file.
• tail command is used to display the last n lines of a file.
• tail -3 filename displays the last 3 lines of the file.
• tail filename displays the last 10 lines of the file.
• | (pipe) passes the output of one command as input to another command.
• ls -lrt | wc -l counts the number of files and directories in the current directory.
• head -4 log | tail -1 displays the 4th line of the file.
• head -99 file | tail -1 displays the 99th line of the file.
• head -7 file | tail -3 displays the 4th to 7th line of the file.
• head -99 log | tail -1 | wc -w counts the number of words in the 99th line of the file.
• tail -2 log | head -1 displays the 2nd last line of the file.

Pattern Searching with grep

• grep is used to search for patterns in files.
• grep "pattern" filenamesearches for the specified pattern in the file.
• grep -w "string" filename searches for the exact word specified.
• grep -i "Linux" test_1 searches case-insensitively for "Linux" in the file.
• grep -e "linux" -e "windows" test_1 searches for either "linux" or "windows".
• egrep command can also be used to search for multiple patterns.
• grep -R -l "linux" * lists the filenames which contain "linux".
• grep -v "linux" test_1 prints lines that don't contain "linux".
• grep "^pattern" filename lists lines starting with "pattern".
• grep "s$" test_1 lists lines ending with "s".
• grep -c "linux" test_1 counts the number of lines containing "linux".

### Replacing Strings with sed

• sed is used to replace strings in files.
• sed 's/linux/unix/g' filename replaces "linux" with "unix" in the file.
• sed -i 's/linux/unix/g' test_1 replaces "linux" with "unix" in the file and saves the changes.
• sed '4s/linux/unix/g' replaces "linux" with "unix" in the 4th line.
• sed '2,6s/linux/unix/g' replaces "linux" with "unix" from the 2nd to 6th line.
• sed '$s/linux/unix/g' replaces "linux" with "unix" in the last line
• sed '4d' test_1 deletes the 4th line of the file.
• sed '$d' test_1 deletes the last line of the file.
• sed '2,6d' test_1 deletes lines from the 2nd to 6th line.
• sed '1d;3d' test_1 deletes the 1st and 3rd line.
• sed -n '3p' test_1 prints the 3rd line.
• sed -n '$p' test_1 prints the last line.
• sed -n '2,6p' test_1 prints lines from the 2nd to 6th line.

Column and Row Based File Cutting

• cut is used to cut files column-wise.
• cut -d " " -f1 data prints the first column.
• cut -d " " -f1,3 data prints the 1st and 3rd column.
• cut -d " " -f3-6 data prints the 3rd to 6th column.
• awk is used to cut files row-wise and column-wise.
• awk -F " " '{print $1}' data prints the first column.
• awk -F " " '{print $NF}' data prints the last column.
• awk -F " " '{print $(NF-1)}' data prints the second last column.

### File Searching with find

• find is used to search for files.
• find . -iname "filename" searches for "filename" case-insensitively.
• find . -type f -mtime +90 lists files modified more than 90 days ago.
• find . -type d -mtime +90 lists directories modified more than 90 days ago.
• find . -mtime +90 lists both files and directories modified more than 90 days ago.
• find . -type d -mtime -90 lists directories modified within 90 days.
• find . -type f -mmin -50 lists files modified within 50 minutes.
• find . -type f -mmin +50 lists files modified 50 minutes ago.
• find . -type f -perm 777 lists files with permissions 777.
• find . -type f -empty lists empty files.
• find . -maxdepth 1 -iname "test1" restricts the search to the first-level directory.
• xargs is used to pass the output of one command as arguments to another command.
• find . -type f -mtime +90 | xargs rm -rf deletes all files modified more than 90 days ago.

### Symbolic Links and Hard Links

• ln is used to create symbolic links and hard links.
• ln -s /home/ec2-user/file1 link1 creates a symbolic link to file1.
• ln /home/ec2-user/file1 hard1 creates a hard link to file1.
• Deleting the actual file breaks a symbolic link but not a hard link.

Process Management

• ps is used to list currently running processes.
• ps -ef | grep "processname" checks if a specific process is running.
• kill -9 PID force-stops a process.
• sleep command can be used to pause execution for a specified duration.
• sudo service name stop stops a service gracefully.
• sudo service name start starts a service.
• sudo service name restart restarts a service.
• sudo systemctl stop name stops a systemd service.

Permissions and Access Control

• umask sets default permissions for newly created files and directories.
• umask 000 sets full permissions (read, write, and execute) for the owner, group, and others.
• umask 777 sets no permissions for the owner, group, and others.
• su username switches to another user or superuser.
• sudo executes a command with root privileges.
• sudo useradd ABC adds a new user ABC.
• sudo passwd ABC sets password for user ABC.
• sudo su - logs in as root user from ec2-user.
• Edit /etc/sudoers.d/90-cloud-init-users to grant sudo permissions to specific users.

Displaying File Content

• more displays the content of a file page by page.
• less also displays content page by page but allows scrolling up and down.

System Date and Time

• date prints current system date and time.
• date +%m prints the current month.

Deleting Duplicate Lines

• uniq prints only unique lines from the input, removing duplicate lines.

Assigment for practice

• Write a command to list files larger than 1 MB.
• Use the -exec option in the find command to delete files larger than 10 MB.
• Write the steps to kill all processes started by a specific user.
• Write the steps to kill all processes with a specific name.
• Write a command to display 99th to 103th line of a file.
• Find all files and directories in the current directory that have been modified within the last 3 days and recursively change their permissions to 755.