What You Need to Know
- Copy, move, and delete files and directories individually.
- Recursively copy and delete multiple files and directories.
- Use simple and extended wildcard patterns in commands.
- Search for files using
findby type, size, and time. - Work with
tar,cpio, anddd.
Copying Files and Directories
cp
cp copies files and directories.
cp source dest # copy a file
cp file1 file2 dir/ # copy multiple files into a directory
cp -r dir1/ dir2/ # recursively copy a directory
cp -p file dest # preserve permissions, owner, timestamps
cp -a dir1/ dir2/ # archive mode: recursive + preserve all attributes (= -dR --preserve=all)
cp -i file dest # prompt before overwriting
cp -u file dest # copy only if source is newer than dest
cp -v file dest # verbose output
cp -l file dest # create a hard link instead of copying
cp -s file dest # create a symbolic link instead of copying
-r (or -R) copies directories recursively. Without it cp will error on a directory.
-a combines -dR --preserve=all: preserves symbolic links, permissions, timestamps, and owner. Use it for full backups.
Moving and Renaming
mv
mv moves files and directories, and renames them.
mv file newname # rename a file
mv file dir/ # move a file into a directory
mv dir1/ dir2/ # move or rename a directory
mv -i file dest # prompt before overwriting
mv -u file dest # move only if source is newer than dest
mv -v file dest # verbose output
mv is atomic within a single filesystem: the file simply gets a new name in the directory tree. Across different filesystems, mv copies the file and removes the original.
Removing Files and Directories
rm
rm file # remove a file
rm file1 file2 # remove multiple files
rm -r dir/ # recursively remove a directory and its contents
rm -f file # force remove without prompt (ignores non-existent files)
rm -rf dir/ # recursive and forced (be careful!)
rm -i file # prompt for each file
rm -v file # verbose output
rmdir
rmdir removes only empty directories.
rmdir dir/ # remove an empty directory
rmdir -p a/b/c # remove a chain of empty directories
If a directory contains even one file, rmdir will error. For non-empty directories use rm -r.
Creating Files and Directories
mkdir
mkdir dir # create a directory
mkdir -p a/b/c # create the full directory chain (-p doesn't error on existing ones)
mkdir -m 755 dir # create a directory with specified permissions
touch
touch creates an empty file or updates the timestamps of an existing one.
touch file # create a file or update atime/mtime to current time
touch -t 202312311230 file # set a specific time (YYYYMMDDhhmm)
touch -d "2023-12-31" file # set a date in readable format
touch -a file # update only atime
touch -m file # update only mtime
Listing Directory Contents
ls
ls # list files in current directory
ls -l # long listing
ls -a # show hidden files (starting with .)
ls -la # long listing with hidden files
ls -lh # sizes in human-readable format (K, M, G)
ls -lt # sort by modification time
ls -lr # reverse sort order
ls -R # recursive listing
ls -i # show inode numbers
ls -d dir/ # show info about the directory itself, not its contents
Globbing and Patterns
File globbing is the shell expanding patterns before passing arguments to a command.
Basic Wildcards
| Character | Meaning |
|---|---|
* | any sequence of characters (including empty) |
? | exactly one character |
[abc] | one character from the set |
[a-z] | one character from the range |
[!abc] | one character not in the set |
[^abc] | same (shell-dependent) |
Examples
ls *.txt # all files with .txt extension
ls file?.log # file1.log, file2.log, but not file10.log
ls report[0-9].pdf # report0.pdf ... report9.pdf
ls [!.]* 2>/dev/null # files not starting with a dot (like ls without -a)
cp *.conf /etc/bak/ # copy all .conf files
rm temp* # remove everything starting with temp
Extended Globbing (extglob)
In bash, extended globbing is enabled with shopt -s extglob:
| Pattern | Meaning |
|---|---|
?(pattern) | zero or one match |
*(pattern) | zero or more matches |
+(pattern) | one or more matches |
@(pattern) | exactly one match |
!(pattern) | anything except the match |
shopt -s extglob
ls !(*.bak) # all files except .bak
Searching with find
find searches the directory hierarchy using various criteria.
Syntax
find [path] [criteria] [action]
By Name and Type
find / -name "*.log" # by name (case-sensitive)
find / -iname "*.log" # by name (case-insensitive)
find / -type f # regular files only
find / -type d # directories only
find / -type l # symbolic links only
find / -name "*.conf" -type f # name + type
By Size
find / -size +100M # larger than 100 megabytes
find / -size -10k # smaller than 10 kilobytes
find / -size 1G # exactly 1 gigabyte
find / -size 100b # exactly 100 bytes
find . -size 0b # empty files (0 bytes)
find . -empty # empty files and directories (shorter)
Size suffixes: c (bytes), k (kilobytes), M (megabytes), G (gigabytes).
By Time
find / -mtime -7 # modified less than 7 days ago
find / -mtime +30 # modified more than 30 days ago
find / -atime -1 # accessed less than 1 day ago
find / -ctime -2 # status changed less than 2 days ago
find / -mmin -60 # modified less than 60 minutes ago
find / -newer /etc/passwd # newer than the specified file
By Permissions and Owner
find / -perm 755 # exact permissions 755
find / -perm -644 # at least permissions 644 (all specified bits set)
find / -perm /111 # at least one of the specified bits set
find / -user username # files owned by user
find / -group groupname # files owned by group
find / -nouser # files with no owner in the system
Actions
find / -name "*.tmp" -delete # delete found files
find / -name "*.sh" -exec chmod +x {} \; # run a command for each file
find / -name "*.log" -exec cp {} /backup/ \; # copy each file
find / -name "core" -exec rm -f {} + # + groups files (more efficient than \;)
find / -name "*.txt" | xargs grep "pattern" # pass results to xargs
{} is replaced by the found filename. \; terminates -exec. + at the end groups arguments like xargs and is faster.
Logical Operators
find / -name "*.log" -and -size +10M # both conditions (AND is default)
find / -name "*.bak" -or -name "*.tmp" # either condition
find / -not -name "*.conf" # negation
find / \( -name "a" -or -name "b" \) # grouping
Identifying File Types
file
file determines a file’s type by examining its content, not its extension.
file document.pdf # PDF document, version 1.4
file script.sh # POSIX shell script
file /bin/ls # ELF 64-bit LSB executable
file image.jpg # JPEG image data
file archive.tar.gz # gzip compressed data
file reads signatures from /etc/magic and /usr/share/misc/magic.
Archiving: tar and cpio
tar
tar (Tape ARchive) creates archives from files and directories.
Creating an Archive
tar -cf archive.tar dir/ # create archive
tar -czf archive.tar.gz dir/ # create + compress with gzip
tar -cjf archive.tar.bz2 dir/ # create + compress with bzip2
tar -cJf archive.tar.xz dir/ # create + compress with xz
tar -cvf archive.tar dir/ # create with verbose output
Viewing Contents
tar -tf archive.tar # list files in archive
tar -tvf archive.tar # detailed listing
Extracting
tar -xf archive.tar # extract to current directory
tar -xzf archive.tar.gz # extract .tar.gz
tar -xjf archive.tar.bz2 # extract .tar.bz2
tar -xf archive.tar -C /dest/ # extract to specified directory
tar -xf archive.tar file.txt # extract only one file
tar Flags (memorize)
| Flag | Meaning |
|---|---|
-c | create |
-x | extract |
-t | list |
-f | file (archive name) |
-z | gzip |
-j | bzip2 |
-J | xz |
-v | verbose |
-C | change directory (extraction target) |
-p | preserve permissions |
--exclude | exclude file/directory |
-f is almost always required. The filename follows immediately after -f.
cpio
cpio (copy in/out) works with a file list from stdin.
# Create archive
find . -name "*.conf" | cpio -ov > backup.cpio
# View contents
cpio -tv < backup.cpio
# Extract
cpio -idv < backup.cpio
# Extract to another directory
(mkdir -p /dest && cd /dest && cpio -idv < /path/backup.cpio)
cpio modes:
-o(out) — create archive-i(in) — extract-p(pass-through) — copy without creating an archive
Copying Data: dd
dd copies data byte by byte. Works with block devices and files.
# Create a disk image
dd if=/dev/sda of=/backup/disk.img
# Restore an image
dd if=/backup/disk.img of=/dev/sda
# Create a partition image
dd if=/dev/sda1 of=partition.img
# Create a file of a given size (filled with zeros)
dd if=/dev/zero of=test.img bs=1M count=100
# Create a file with random data
dd if=/dev/urandom of=random.bin bs=1M count=10
# Create a bootable USB
dd if=linux.iso of=/dev/sdb bs=4M status=progress
# Convert case
dd if=input.txt of=output.txt conv=ucase
dd parameters:
| Parameter | Meaning |
|---|---|
if= | input file (source) |
of= | output file (destination) |
bs= | block size |
count= | number of blocks |
skip= | skip blocks at start of input |
seek= | skip blocks at start of output |
conv= | conversion (ucase, lcase, notrunc, sync…) |
status=progress | show progress |
File Compression
gzip and gunzip
gzip compresses files, replacing the original with .gz.
gzip file.txt # creates file.txt.gz, removes file.txt
gzip -k file.txt # keep the original file
gzip -d file.txt.gz # decompress (= gunzip)
gzip -1 file.txt # fast compression (weak)
gzip -9 file.txt # maximum compression (slow)
gzip -l file.txt.gz # show archive info
gunzip file.txt.gz # decompress
zcat file.txt.gz # read without decompressing
bzip2 and bunzip2
bzip2 gives better compression than gzip but is slower.
bzip2 file.txt # creates file.txt.bz2, removes file.txt
bzip2 -k file.txt # keep the original file
bzip2 -d file.txt.bz2 # decompress (= bunzip2)
bzip2 -1 file.txt # fast compression
bzip2 -9 file.txt # maximum compression
bunzip2 file.txt.bz2 # decompress
bzcat file.txt.bz2 # read without decompressing
xz
xz provides the best compression of the three, but is the slowest.
xz file.txt # creates file.txt.xz
xz -d file.txt.xz # decompress
xz -k file.txt # keep original
xzcat file.txt.xz # read without decompressing
Exam Quick Reference
# cp
cp -r src/ dst/ # recursive copy
cp -a src/ dst/ # archive mode (preserves everything)
cp -i *.txt /backup/ # copy with prompt
# find — most common patterns
find /home -name "*.txt" -type f
find /var -size +50M -mtime -7
find / -perm -4000 -type f # find SUID files
find . -name "*.tmp" -delete
find . -name "*.sh" -exec chmod +x {} \;
# tar — remember order: operation, then modifiers, then -f
tar -czf backup.tar.gz /home/user/
tar -xzf backup.tar.gz -C /restore/
tar -tf archive.tar
# dd — disk copying
dd if=/dev/sda of=disk.img bs=4M status=progress
# gzip/bzip2
gzip -k largefile.log # compress, keeping original
tar -czf backup.tar.gz dir/ # most often used through tar
Exam Tips
Recursively remove a directory: rm -rf dir/ (not rmdir).
Preserve permissions when copying: cp -a or cp -p.
Find files larger than 1 GB: find / -size +1G.
Find files modified in the last 2 days: find / -mtime -2.
Create an archive compressed with bzip2: tar -cjf arch.tar.bz2 dir/.
Extract .tar.gz to /tmp: tar -xzf arch.tar.gz -C /tmp/.
View archive contents without extracting: tar -tf arch.tar.
Difference between mtime, atime, ctime:
mtime— time of last file content modification.atime— time of last file access.ctime— time of last metadata change (permissions, owner).
What touch does to an existing file: updates its timestamps to the current time.
Difference between cpio and tar: cpio reads a file list from stdin; tar takes filenames directly.
dd conv=notrunc: do not truncate the output file when writing.
Exercises
Guided Exercises
1. Analyzing ls -lh Output
Given the output of ls -lh:
total 60K
drwxr-xr-x 2 frank frank 4.0K Apr 1 2018 Desktop
drwxr-xr-x 2 frank frank 4.0K Apr 1 2018 Documents
-rw-r--r-- 1 frank frank 21 Sep 7 12:59 emp_name
-rw-r--r-- 1 frank frank 20 Sep 7 13:03 emp_salary
-rw-r--r-- 1 frank frank 8.8K Apr 1 2018 examples.desktop
-rw-r--r-- 1 frank frank 10 Sep 1 2018 file1
What does the d at the start of a line mean?
Answer
d marks a directory. A regular file uses -, a special character device uses c.
Why are sizes displayed in human-readable format?
Answer
Because of the -h flag. Without it sizes would be in bytes.
How would the output of plain ls differ?
Answer
Only filenames would be shown — no permissions, owner, size, or date.
2. Copying and Moving
Given:
cp /home/frank/emp_name /home/frank/backup
What happens to emp_name on success?
Answer
emp_name is copied into the backup directory. The original file stays in place.
If emp_name were a directory, which flag would cp need?
Answer
-r (recursive). Without it cp refuses to copy a directory with the message omitting directory.
If cp were replaced with mv, what changes?
Answer
emp_name would be moved into backup. It would no longer exist in frank’s home directory.
3. Removing with a Wildcard
Given a directory with:
file1.txt file2.txt file3.txt file4.txt
Which wildcard removes everything with one command?
Answer
The asterisk *:
rm *
* matches any number of any characters, including empty — it captures all files.
4. ls with a Wildcard
Which files does ls file*.txt list from the same directory?
Answer
All four: file1.txt, file2.txt, file3.txt, file4.txt. The asterisk matches any number of characters, including a single digit.
5. Bracket Globbing
Complete the command to list all four files (file1.txt…file4.txt):
ls file[].txt
Answer
ls file[0-9].txt
[0-9] is a range matching one digit from 0 to 9. [1-4] or [1234] also work.
6. Analyzing find -type d Output
Given:
$ find /home/frank/Documents/ -type d
/home/frank/Documents/
/home/frank/Documents/animal
/home/frank/Documents/animal/domestic
/home/frank/Documents/animal/wild
What type of files does this command list?
Answer
Only directories. The -type d flag restricts results to directories.
Where does the search start?
Answer
/home/frank/Documents.
7. Missing tar Flag
A user wants to create a compressed archive:
tar cvf /home/frank/backup.tar.gz /home/frank/dir1
Which flag is missing for gzip compression?
Answer
-z. Without it tar creates a plain uncompressed archive despite the .gz extension. The correct command:
tar -czvf /home/frank/backup.tar.gz /home/frank/dir1
Explorational Exercises
1. Create Files dog and cat
Task: In your home directory, create files named dog and cat.
Answer
touch dog cat
touch creates empty files with current timestamps. Multiple names can be passed in one command.
2. Create a Directory and Move Files
Task: Create an animal directory and move dog and cat into it.
Answer
mkdir animal
mv dog cat -t animal/
-t specifies the target directory explicitly — convenient when moving multiple files. mv dog cat animal/ also works.
3. Create backup Inside Documents
Task: Go to ~/Documents and create a backup directory there.
Answer
cd ~/Documents
mkdir backup
4. Recursive Copy
Task: Copy animal together with its contents into backup.
Answer
cp -r animal ~/Documents/backup
-r copies the directory recursively. Without this flag cp errors with omitting directory.
5. Rename Inside backup
Task: Rename animal inside backup to animal.bkup.
Answer
mv animal/ animal.bkup
Run inside the backup directory. mv renames a directory the same way it renames a file.
6. List Specific Archives
Task: The directory /home/lpi/databases contains many files including db-1.tar.gz, db-2.tar.gz, and db-3.tar.gz. List only those three with a single command.
Answer
ls db-[1-3].tar.gz
[1-3] matches exactly one character in the range 1–3, which precisely excludes all other files.
7. Remove Only PDFs
Task: Given a directory:
cne1222223.pdf cne12349.txt cne1234.pdf
Remove only .pdf files using a single glob character.
Answer
rm *.pdf
* matches any name before .pdf. The .txt file is untouched.
8. Find and Delete Large Backup Files
Task: Find files with the .backup extension in /var.
Answer
find /var -name "*.backup"
Task: Narrow it down: find only .backup files between 100M and 1000M in size.
Answer
find /var -name "*.backup" -size +100M -size -1000M
Two -size conditions combine as AND: the file must be strictly larger than 100M and strictly smaller than 1000M.
Task: Add deletion of the found files to the previous command.
Answer
find /var -name "*.backup" -size +100M -size -1000M -delete
-delete removes each found file directly without spawning an external process. Use it only after verifying the search returns exactly the files you intend to delete.
9. Archive Multiple Files
Four files are in /var:
db-jan-2018.backup
db-feb-2018.backup
db-march-2018.backup
db-apr-2018.backup
Task: Create an archive db-first-quarter-2018.backup.tar from all four files.
Answer
tar -cvf db-first-quarter-2018.backup.tar db-jan-2018.backup db-feb-2018.backup db-march-2018.backup db-apr-2018.backup
tar accepts multiple files separated by spaces. All of them go into the single archive.
Task: Create the same archive but compressed with gzip. The filename should end in .gz.
Answer
tar -zcvf db-first-quarter-2018.backup.tar.gz db-jan-2018.backup db-feb-2018.backup db-march-2018.backup db-apr-2018.backup
The -z flag adds gzip compression. The .tar.gz extension indicates a tar archive compressed with gzip.
Topic 103: GNU and Unix Commands