> For the complete documentation index, see [llms.txt](https://cajac.gitbook.io/ctf-notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://cajac.gitbook.io/ctf-notes/getting-help/getting-help-in-bash.md). # Getting Help in Bash ## -h or --help parameters Most commands support the `-h` and/or `--help` parameters for short information with a list of supported parameters. ## apropos **apropos** searches the manual page names and descriptions. ```bash ┌──(kali㉿kali)-[~] └─$ apropos uname arch (1) - print machine hardware name (same as uname -m) archive_entry_perms (3) - functions for manipulating ownership and permissions in archive entry descriptions archive_read_disk (3) - functions for reading objects from disk oldolduname (2) - get name and information about current kernel olduname (2) - get name and information about current kernel uname (1) - print system information uname (2) - get name and information about current kernel ``` ## help help displays information about built-in commands Example help for the `help` built-in ```bash help: help [-dms] [pattern ...] Display information about builtin commands. Displays brief summaries of builtin commands. If PATTERN is specified, gives detailed help on all commands matching PATTERN, otherwise the list of help topics is printed. Options: -d output short description for each topic -m display usage in pseudo-manpage format -s output only a short usage synopsis for each topic matching PATTERN Arguments: PATTERN Pattern specifying a help topic Exit Status: Returns success unless PATTERN is not found or an invalid option is given. ``` {% hint style="info" %} NOTE\ The help built-in is NOT available in zsh! {% endhint %} ## info **info** reads Info documents but it's not installed by default on Kali Linux. \ Use `sudo apt install info` if needed. Example of main info page ``` File: dir, Node: Top, This is the top of the INFO tree. This is the Info main menu (aka directory node). A few useful Info commands: 'q' quits; 'H' lists all Info commands; 'h' starts the Info tutorial; 'mTexinfo RET' visits the Texinfo manual, etc. * Menu: Basics * Common options: (coreutils)Common options. * Coreutils: (coreutils). Core GNU (file, text, shell) utilities. * Date input formats: (coreutils)Date input formats. * File permissions: (coreutils)File permissions. Access modes. * Finding files: (find). Operating on files matching certain criteria. Compression * Gzip: (gzip). General (de)compression of files (lzw). Development * Com_err: (com_err). A Common Error Description Library for UNIX. * SSIP: (ssip). Speech Synthesis Interface Protocol. * Speech Dispatcher: (speech-dispatcher). Speech Dispatcher. * bzip2 and libbzip2, version 1.0.8: (manual). A program and library for data compression * libext2fs: (libext2fs). The EXT2FS library. * libffi: (libffi). Portable foreign function interface library. Editors * hexeditor: (hexeditor). Binary ascii/ebcdic terminal hex editor. * nano: (nano). Small and friendly text editor. Encryption * Nettle: (nettle). A low-level cryptographic library. General Commands * Screen: (screen). Full-screen window manager. * netmask: (netmask). A netmask generation and conversion program. GNU organization * Maintaining Findutils: (find-maint). Maintaining GNU findutils GNU Utilities * dirmngr-client: (gnupg). X.509 CRL and OCSP client. -----Info: (dir)Top, 274 lines --Top------------------------------------------------------------------------------------------------------------------------------------------ Welcome to Info version 7.1.1. Type H for help, h for tutorial. ``` In the info system you use: * Arrow keys (Up, Down, Left, Right) to move within a section or to the next/previous one * `q` to quit the session * `H` to get Help * `h` to start a tutorial * `Enter` to select a "link" (underlined text) * `Home` or `b` (beginning) to go to the top of the page * `End` or `e` (end) to go to the bottom of the page * `Page Up` to go up one screenful * `Page Down` to go down one screenful * `[` to go to the previous node in the document * `]` to go to the next node in the document * `u` to go up one level * `t` to go to the top of this document * `d` to go to the main directory node ## man **man** is an interface to the system reference manuals. To get the manual page for `uname` ```bash man uname ``` To get the manual page for `open` with a specific section (2 in this case) ```bash man 2 open man open.2 ``` The sections are as follows:
SectionContents
1User Commands
2Programming interfaces for kernel system calls
3Programming interfaces to the C library
4Special files such as device nodes and drivers
5File formats
6Games and amusements such as screen-savers
7Miscellaneous
8System administration commands
To search for a specific keyword in the man pages (architecture in this case) ```bash ┌──(kali㉿kali)-[~] └─$ man -k architecture __ppc_get_timebase (3) - get the current value of the Time Base Register on Power architecture and its frequency. __ppc_get_timebase_freq (3) - get the current value of the Time Base Register on Power architecture and its frequency. __setfpucw (3) - set FPU control word on i386 architecture (obsolete) arch_prctl (2) - set architecture-specific thread state dpkg-architecture (1) - set and determine the architecture for package building Dpkg::Arch (3perl) - handle architectures exa (4) - new 2D acceleration architecture for X.Org i386 (8) - change reported architecture in new program environment and/or set personality flags linux32 (8) - change reported architecture in new program environment and/or set personality flags linux64 (8) - change reported architecture in new program environment and/or set personality flags lscpu (1) - display information about the CPU architecture numa (7) - overview of Non-Uniform Memory Architecture pbmtoppa (1) - convert PBM image to HP Printer Performance Architecture (PPA) proc_cpuinfo (5) - CPU and system architecture information s390_guarded_storage (2) - operations with z/Architecture guarded storage facility setarch (8) - change reported architecture in new program environment and/or set personality flags x86_64 (8) - change reported architecture in new program environment and/or set personality flags ``` The keyword can be a regular expression which can help to narrow down the search ```bash kali@kali:~$ man -k '^passwd$' passwd (1) - change user password passwd (1ssl) - compute password hashes passwd (5) - the password file ``` ## tldr The [**tldr** pages](https://tldr.sh/) are a community effort to simplify the beloved [man pages](https://en.wikipedia.org/wiki/Man_page) with practical examples. It is not installed by default on Kali. Use `sudo apt install tldr` if needed. ```bash ┌──(kali㉿kali)-[~] └─$ tldr dig Downloading tldr pages to /home/kali/.local/share/tldr dig DNS lookup utility. More information: https://manned.org/dig. - Lookup the IP(s) associated with a hostname (A records): dig +short example.com - Get a detailed answer for a given domain (A records): dig +noall +answer example.com - Query a specific DNS record type associated with a given domain name: dig +short example.com A|MX|TXT|CNAME|NS - Specify an alternate DNS server to query and optionally use DNS over TLS (DoT): dig +tls @1.1.1.1|8.8.8.8|9.9.9.9|... example.com - Perform a reverse DNS lookup on an IP address (PTR record): dig -x 8.8.8.8 - Find authoritative name servers for the zone and display SOA records: dig +nssearch example.com - Perform iterative queries and display the entire trace path to resolve a domain name: dig +trace example.com - Query a DNS server over a non-standard [p]ort using the TCP protocol: dig +tcp -p port @dns_server_ip example.com ``` ## type **type** writes a description of command type. ```bash ┌──(kali㉿kali)-[~] └─$ type read read is a shell builtin ┌──(kali㉿kali)-[~] └─$ type uname uname is /usr/bin/uname ┌──(kali㉿kali)-[~] └─$ type ll ll is an alias for ls -l ``` ## whatis **whatis** displays one-line manual page descriptions. ```bash ┌──(kali㉿kali)-[~] └─$ whatis ls ls (1) - list directory contents ┌──(kali㉿kali)-[~] └─$ whatis apropos apropos (1) - search the manual page names and descriptions ┌──(kali㉿kali)-[~] └─$ whatis whatis whatis (1) - display one-line manual page descriptions ``` ## which **which** shows the full path of (shell) commands. ```bash ┌──(kali㉿kali)-[~] └─$ which ls ls: aliased to ls --color=auto ┌──(kali㉿kali)-[~] └─$ which read read: shell built-in command ┌──(kali㉿kali)-[~] └─$ which -a nmap /usr/bin/nmap /bin/nmap ``` ## Resources **apropos** - Linux manual page: **info** - Linux manual page: **man** - Linux manual page: **type** - Linux manual page: **whatis** - Linux manual page: **which** - Linux manual page: