# Archiving and Compressing Files ## Overview In Linux, **archiving** and **compression** are two different operations: 1. **Archiving** = Combine multiple files/directories into a single file. 2. **Compression** = Reduce the size of that file. ```text Files/Directories │ ▼ tar │ ▼ archive.tar │ ▼ gzip │ ▼ archive.tar.gz ``` --- # 1. gzip `gzip` (GNU Zip) is a compression utility. A file ending in `.gz` is a gzip-compressed file. ## Compress a File ```bash gzip file ``` Result: ```text file.gz ``` ## Decompress a File ```bash gunzip file.gz ``` Result: ```text file ``` ## Important `gzip` does **not** create archives. It can only compress a single file. ```text report.txt │ ▼ gzip │ ▼ report.txt.gz ``` --- # 2. tar `tar` (Tape Archive) is used for archiving files and directories. Unlike `gzip`, `tar` can package multiple files and directories into a single archive. ## Create an Archive ```bash tar cvf archive.tar file1 file2 dir1 ``` Result: ```text archive.tar ``` --- # Understanding tar Options ## c = Create Create a new archive. ```bash tar cvf archive.tar files ``` --- ## x = Extract Extract files from an archive. ```bash tar xvf archive.tar ``` --- ## t = Table of Contents List files inside an archive without extracting. ```bash tar tvf archive.tar ``` --- ## v = Verbose Show files being processed. ```bash tar xvf archive.tar ``` Example output: ```text file1 file2 dir1/file3 ``` ### Double Verbose Some tar versions support: ```bash tar xvvf archive.tar ``` Shows additional details such as: - Permissions - Ownership - File size --- ## f = File Specifies the archive file name. ```bash tar cvf archive.tar files ``` The argument immediately after `f` must be the archive filename. --- # Creating Archives Suppose we have: ```text project/ ├── app.py ├── config.yaml └── README.md ``` Create archive: ```bash tar cvf project.tar project/ ``` Result: ```text project.tar ``` --- # Extracting Archives Extract all files: ```bash tar xvf project.tar ``` Result: ```text project/ ├── app.py ├── config.yaml └── README.md ``` --- # Extracting Specific Files You can extract specific items if you know their exact names. ```bash tar xvf project.tar project/config.yaml ``` --- # Important Note Extracting does **not** remove the archive itself. Before: ```text project.tar ``` After extraction: ```text project.tar project/ ``` The archive remains. --- # Table of Contents Mode Before extracting, it is a good practice to inspect the archive. ```bash tar tvf project.tar ``` Example: ```text project/ project/app.py project/config.yaml project/README.md ``` --- # Why Check Contents First? A badly structured archive may dump files directly into the current directory. Good archive: ```text project/ project/file1 project/file2 ``` Bad archive: ```text file1 file2 file3 ``` Extracting the bad archive may clutter your current directory. ### Recommendation Create a temporary directory first: ```bash mkdir temp cd temp tar xvf ../archive.tar ``` --- # Preserving Permissions Use the `p` option when extracting: ```bash tar xvpf archive.tar ``` This preserves: - File permissions - Ownership information Useful for: - Backups - System restores - Configuration archives --- # Important Root User Note When extracting as root: ```bash sudo tar xvpf archive.tar ``` **Do not interrupt tar before it finishes.** Reason: - tar checks the archive completely - Permissions may be applied near the end - Interrupting can leave files with incorrect permissions or ownership Always wait until the shell prompt returns: ```bash $ ``` before assuming extraction is complete. --- # Compressed Archives (.tar.gz) Most Linux archives are distributed as: ```text file.tar.gz ``` Meaning: ```text tar archive + gzip compression ``` --- # Manual Extraction Process Work from right to left. ## Step 1: Remove .gz ```bash gunzip file.tar.gz ``` Produces: ```text file.tar ``` ## Step 2: Extract .tar ```bash tar xvf file.tar ``` --- # Creating a .tar.gz Archive Reverse the process. ## Step 1: Create Archive ```bash tar cvf file.tar project/ ``` ## Step 2: Compress Archive ```bash gzip file.tar ``` Result: ```text file.tar.gz ``` --- # zcat The previous approach creates a temporary `.tar` file. This: - Uses extra disk space - Requires extra I/O operations A more efficient method is: ```bash zcat file.tar.gz | tar xvf - ``` --- # What is zcat? Equivalent to: ```bash gunzip -dc file.tar.gz ``` Options: ```text -d = decompress -c = write output to stdout ``` --- # Understanding the Pipeline ```bash zcat file.tar.gz | tar xvf - ``` Flow: ```text file.tar.gz │ ▼ zcat │ ▼ decompressed tar stream │ ▼ tar │ ▼ extracted files ``` No temporary `.tar` file is created. --- # Meaning of "-" In: ```bash tar xvf - ``` The dash means: ```text Read archive data from standard input (stdin) ``` instead of reading from a physical file. --- # tar's Built-in gzip Shortcut Because `.tar.gz` files are extremely common, tar can call gzip automatically. Instead of: ```bash zcat file.tar.gz | tar xvf - ``` Use: ```bash tar xzvf file.tar.gz ``` --- # The z Option ```text z = use gzip automatically ``` Works with: - c (create) - x (extract) - t (list) --- # Common tar.gz Commands ## Create ```bash tar czvf backup.tar.gz backup/ ``` Meaning: ```text c = create z = gzip v = verbose f = filename ``` --- ## Extract ```bash tar xzvf backup.tar.gz ``` Meaning: ```text x = extract z = gunzip automatically v = verbose f = filename ``` --- ## View Contents ```bash tar ztvf backup.tar.gz ``` Meaning: ```text t = table of contents z = gunzip automatically v = verbose f = filename ``` --- # .tgz Files A: ```text file.tgz ``` is exactly the same as: ```text file.tar.gz ``` The `.tgz` extension exists mainly for compatibility with older FAT/MS-DOS filesystems. --- # Other Compression Utilities ## xz Compress: ```bash xz file ``` Result: ```text file.xz ``` Decompress: ```bash unxz file.xz ``` --- ## bzip2 Compress: ```bash bzip2 file ``` Result: ```text file.bz2 ``` Decompress: ```bash bunzip2 file.bz2 ``` --- ## Comparison ```text gzip -> Fast compression/decompression bzip2 -> Better compression, slower xz -> Best compression, usually slowest ``` --- # ZIP Archives Linux also supports Windows ZIP archives. ## Create ZIP ```bash zip archive.zip file1 file2 ``` ## Extract ZIP ```bash unzip archive.zip ``` Supports: - `.zip` - Self-extracting `.exe` archives --- # Legacy .Z Files Files ending with: ```text file.Z ``` were created using the old Unix `compress` utility. Decompress: ```bash gunzip file.Z ``` Modern `gzip` can unpack `.Z` files but does not create them. --- # Commands to Memorize ## gzip ```bash gzip file gunzip file.gz ``` ## tar ```bash tar cvf archive.tar dir/ tar xvf archive.tar tar tvf archive.tar ``` ## tar + gzip ```bash tar czvf archive.tar.gz dir/ tar xzvf archive.tar.gz tar ztvf archive.tar.gz ``` ## Streaming ```bash zcat archive.tar.gz | tar xvf - ``` --- # Interview One-Liners ### What is gzip? > gzip compresses a file but does not combine multiple files into an archive. ### What is tar? > tar combines multiple files/directories into a single archive without compressing them. ### What is .tar.gz? > A `.tar.gz` file is a tar archive that has been compressed using gzip. ### What does zcat do? > zcat decompresses a gzip file and writes the result to standard output. ### Difference Between tar and gzip | tar | gzip | |------|------| | Creates archives | Compresses files | | Combines multiple files | Works on a single file | | Produces `.tar` | Produces `.gz` | | No compression by default | Compression only |