Linux Notes

Common Commands

Syntax

less

Similar to more, it lets you browse files freely and supports paging and searching Format: less [options] file Option description:

• -b Set the size of the buffer
• -e Automatically quit when the file has been displayed
• -f Force opening special files, such as peripheral device designators, directories, and binary files
• -g Only highlight the last searched keyword
• -i Ignore case when searching
• -m Show a percentage similar to the more command
• -N Show the line number of each line
• -o Save the content output by less in the specified file
• -Q Do not use warning sounds
• -s Display consecutive blank lines as a single line
• -S When a line is too long, discard the overflow portion
• -x Display the “tab” key as the specified number of spaces
• /string: The function of searching downward for “string”
• ?string: The function of searching upward for “string”
• n: Repeat the previous search (related to / or ?)
• N: Repeat the previous search in reverse (related to / or ?)
• b Scroll up one page
• d Scroll down half a page
• h Show the help screen
• Q Quit the less command
• u Scroll forward half a page
• y Scroll forward one line
• Space key Scroll one page
• Enter key Scroll one line
• [Page Down]: Scroll down one page
• [Page Up]: Scroll up one page

head

Used to view the beginning of a file Format: head [options] [file] Options:

• -q Hide the file name
• -v Show the file name
• -c The number of bytes to display.
• -n The number of lines to display.

tail

View the content of a file Format: tail options file Options:

• -f Loop reading
• -q Do not display processing information
• -v Display detailed processing information
• -c The number of bytes to display
• -n Display the last n lines of the file
• —pid=PID Used together with -f, meaning it ends after the process with the ID, PID, dies
• -q, —quiet, —silent Never output headers giving the file names
• -s, —sleep-interval=S Used together with -f, meaning it sleeps S seconds between each repetition

file

Used to identify the type of a file Format: file -bcLvz -f -m … file or directory Options:

• -b 　When listing the identification results, do not display the file name.
• -c 　Display the command execution process in detail, for troubleshooting or analyzing the program execution.
• -f 　Specify a name file; when its content has one or more file names, let file identify these files in sequence, with one file name per line as the format.
• -L 　Directly display the category of the file that the symbolic link points to.
• -m 　Specify the magic number file.
• -v 　Display version information.
• -z 　Try to interpret the content of compressed files.
• file or directory…: The list of files whose type is to be determined; separate multiple files with spaces, and shell wildcards can be used to match multiple files.

In

Full name: link files — creates a synchronized link for a file at another location Format: in options source file or directory target file or directory Command options Required options:

• —backup[=CONTROL] Back up existing target files
• -b Similar to —backup, but does not accept parameters
• -d Allow the superuser to make hard links to directories
• -f Force execution
• -i Interactive mode; if the file exists, prompt the user whether to overwrite
• -n Treat symbolic links as ordinary directories
• -s Soft link (symbolic link)
• -v Display the detailed processing process

Optional options:

• -S “-S ” or “—suffix=”
• -V “-V” or “—version-control=”
• —help Display help information
• —version Display version information

tar

Full name: tape archive — used for backing up and packaging files Format: tar options -f archive.tar files……

• -f archive.tar: Specify the name of the archive file.
• [files...]: The files and directories to be packaged.

options parameters

Basic operation options

• -c: Create a new archive file.
• -x: Extract the archive file.
• -t: List the contents of the archive file.
• -r: Append files to an existing archive file.
• -u: Only append files that are newer than the existing files in the archive file.
• -d: Find differences in the archive file that are not synchronized with the file system.
• -A: Append one .tar file to another .tar file.

File selection and exclusion

• -f <file>: Specify the name of the archive file (must be placed at the end of the option list).
• -C <directory>: Switch to the specified directory for operations.
• --exclude=<pattern>: Exclude files matching the specified pattern.
• --exclude-from=<file>: Read the patterns to be excluded from the specified file.
• --exclude-caches: Exclude cache files in directories.
• --exclude-backups: Exclude backup files ending with ~.
• --exclude-vcs: Exclude files generated by version control systems (such as .git, .svn, etc.).

Compression and extraction options

• -z: Compress the archive file using gzip.
• -j: Compress the archive file using bzip2.
• -J: Compress the archive file using xz.
• --lzip: Compress the archive file using lzip.
• --lzma: Compress the archive file using lzma.
• --lzop: Compress the archive file using lzop.
• --zstd: Compress the archive file using zstd.
• -a: Automatically select the compression method (based on the extension of the archive file, such as .tar.gz, .tar.bz2, etc.).
• -I <command>: Use the specified compression program for compression or extraction.

Output and interaction options

• -v: Display the detailed operation process (verbose).
• --progress: Display a progress bar (when used together with -v).
• -w or --interactive: Ask the user for confirmation before each operation.
• --checkpoint: Display a checkpoint after processing each file.
• --checkpoint-action=<action>: Execute the specified action at a checkpoint, such as echo, dot, etc.
• --totals: Display the total number of bytes processed after the operation ends.
• --verbose: Display the processing information in detail.
• --quiet: Output as little information as possible.

File and permission related options

• -p: Preserve the original permissions of files (when extracting).
• --same-owner: Try to set the extracted files to the original owner (requires superuser privileges).
• --no-same-owner: Do not set the file owner.
• --same-permissions: Preserve the original permissions of files (same as -p).
• --no-same-permissions: Do not preserve the original permissions; use the current user’s umask to set permissions.
• -m: Do not restore the modification time of files when extracting, but use the current time.

Archive management options

• -k or --keep-old-files: Keep existing files when extracting; do not overwrite.
• --overwrite: Force overwriting existing files when extracting.
• --remove-files: Delete the original files after a successful archive.
• --delete: Delete the specified files from the archive file (only gnu tar).
• --keep-newer-files: Keep files that are newer than those in the archive when extracting.
• --listed-incremental=<file>: Create an incremental backup or restore from an incremental backup.

File system and device options

• -L <N>: Split archive files larger than N bytes (for tape drives).
• --tape-length=<number>: Specify the tape length (for tape drives).
• --multi-volume: Create or restore multi-volume archive files.
• -M: Used together with --multi-volume to handle multi-volume archive files.
• --use-compress-program=<prog>: Use the specified compression program.

Other useful options

• --transform=<expression>: Rename files in the archive.
• --strip-components=<number>: Strip the specified number of path components when extracting.
• --ignore-failed-read: Ignore read errors and continue the operation.
• --occurrence=<number>: Select the number-th occurrence of a file in the archive.
• -S: Handle sparse files (only archive the blocks actually used).
• --no-recursion: Do not recurse into directories.
• -h or --dereference: Archive the files that symbolic links point to rather than the links themselves.

Help and version information

• --help: Display help information.
• --version: Display the version information of tar.

mkdir

Full name: make directory — used to create directories Format: mkdir -p dirName

Options

• -p: Create a multi-level directory structure; if the parent directory does not exist, it will be created automatically
• -m: Set permissions, e.g., mkdir -m 755 my_directory
• -Z: Set the security context for the directory
• -v: Display detailed information, including the directories being created
• -Z: Set the security context for the directory
• --help: Display help information.
• --version: Display the version information of tar.

awk

A powerful text processing tool Format: awk options ‘pattern {acation}’ file Option parameter description:

• options: These are the options used to control the behavior of awk.
• pattern: This is the pattern used to match the input data. If omitted, awk operates on all lines.
• : This is the action executed on the lines that match the pattern. If omitted, the default action is to print the entire line.

options parameter description:

• -F <separator> or --field-separator=<separator>: Specify the input field separator; the default is a space or a tab. For example, awk -F: ‘{print $1}’ /etc/passwd uses the colon as the separator and prints the first field of each line of the /etc/passwd file.
• -v <variable name>=<value>: Define a variable for the awk script. For example, awk -v var=10 '{print $1 + var}' file.txt sets the variable var to 10 and adds 10 to the first field of each line in the file.
• -f <script file>: Specify a file containing the awk script. For example, awk -f script.awk data.txt executes the script in script.awk to process the data.txt file.
• -V or --version: Display the version information of awk.
• -h or --help: Display the help information of awk, including options and usage examples.