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How to use help command in Linux
In this article, we are going to discuss how to use help command in linux. We will see various ways how you can use the help option while navigating with shell or prompt in Linux.
help command in linux
$ help GNU bash, version 4.3.28(1)-release (i686-pc-linux-gnu) These shell commands are defined internally. Type `help' to see this list. Type `help name' to find out more about the function `name'. Use `info bash' to find out more about the shell in general. Use `man -k' or `info' to find out more about commands not in this list. A star (*) next to a name means that the command is disabled. job_spec [&] history [-c] [-d offset] [n] or history -anrw [filename] or histor> (( expression )) if COMMANDS; then COMMANDS; [ elif COMMANDS; then COMMANDS; ]... [> . filename [arguments] jobs [-lnprs] [jobspec ...] or jobs -x command [args] : kill [-s sigspec | -n signum | -sigspec] pid | jobspec ... or kill> [ arg... ] let arg [arg ...] [[ expression ]] local [option] name[=value] ... alias [-p] [name[=value] ... ] logout [n] bg [job_spec ...] mapfile [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callbac> bind [-lpsvPSVX] [-m keymap] [-f filename] [-q name] [-u name] [-r > popd [-n] [+N | -N] break [n] printf [-v var] format [arguments] builtin [shell-builtin [arg ...]] pushd [-n] [+N | -N | dir] caller [expr] pwd [-LP] case WORD in [PATTERN [| PATTERN]...) COMMANDS ;;]... esac read [-ers] [-a array] [-d delim] [-i text] [-n nchars] [-N nchars> cd [-L|[-P [-e]] [-@]] [dir] readarray [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callb> command [-pVv] command [arg ...] readonly [-aAf] [name[=value] ...] or readonly -p compgen [-abcdefgjksuv] [-o option] [-A action] [-G globpat] [-W w> return [n] complete [-abcdefgjksuv] [-pr] [-DE] [-o option] [-A action] [-G gl> select NAME [in WORDS ... ;] do COMMANDS; done compopt [-o|+o option] [-DE] [name ...] set [-abefhkmnptuvxBCHP] [-o option-name] [--] [arg ...] continue [n] shift [n] coproc [NAME] command [redirections] shopt [-pqsu] [-o] [optname ...] declare [-aAfFgilnrtux] [-p] [name[=value] ...] source filename [arguments] dirs [-clpv] [+N] [-N] suspend [-f] disown [-h] [-ar] [jobspec ...] test [expr] echo [-neE] [arg ...] time [-p] pipeline enable [-a] [-dnps] [-f filename] [name ...] times eval [arg ...] trap [-lp] [[arg] signal_spec ...] exec [-cl] [-a name] [command [arguments ...]] [redirection ...] true exit [n] type [-afptP] name [name ...] export [-fn] [name[=value] ...] or export -p typeset [-aAfFgilrtux] [-p] name [=value] ... false ulimit [-SHabcdefilmnpqrstuvxT] [limit] fc [-e ename] [-lnr] [first] [last] or fc -s [pat=rep] [command] umask [-p] [-S] [mode] fg [job_spec] unalias [-a] name [name ...] for NAME [in WORDS ... ] ; do COMMANDS; done unset [-f] [-v] [-n] [name ...] for (( exp1; exp2; exp3 )); do COMMANDS; done until COMMANDS; do COMMANDS; done function name { COMMANDS ; } or name () { COMMANDS ; } variables - Names and meanings of some shell variables getopts optstring name [arg] wait [-n] [id ...] hash [-lr] [-p pathname] [-dt] [name ...] while COMMANDS; do COMMANDS;done help [-dms] [pattern ...] { COMMANDS ; }
ls command in linux
ls command in linux is one of the most versatile commands which is extremely important in terms of navigation through shell prompt. It has an extensive list of switches associated with it.
$ls --help Usage: ls [OPTION]... [FILE]... List information about the FILEs (the current directory by default). Sort entries alphabetically if none of -cftuvSUX nor --sort. Mandatory arguments to long options are mandatory for short options too. -a, --all do not ignore entries starting with . -A, --almost-all do not list implied . and .. --author with -l, print the author of each file -b, --escape print octal escapes for nongraphic characters --block-size=SIZE use SIZE-byte blocks. See SIZE format below -B, --ignore-backups do not list implied entries ending with ~ -c with -lt: sort by, and show, ctime (time of last modification of file status information) with -l: show ctime and sort by name otherwise: sort by ctime -C list entries by columns --color[=WHEN] colorize the output. WHEN defaults to `always' or can be `never' or `auto'. More info below -d, --directory list directory entries instead of contents, and do not dereference symbolic links -D, --dired generate output designed for Emacs' dired mode -f do not sort, enable -aU, disable -ls --color -F, --classify append indicator (one of */=>@|) to entries --file-type likewise, except do not append `*' --format=WORD across -x, commas -m, horizontal -x, long -l, single-column -1, verbose -l, vertical -C --full-time like -l --time-style=full-iso -g like -l, but do not list owner --group-directories-first group directories before files. augment with a --sort option, but any use of --sort=none (-U) disables grouping -G, --no-group in a long listing, don't print group names -h, --human-readable with -l, print sizes in human readable format (e.g., 1K 234M 2G) --si likewise, but use powers of 1000 not 1024 -H, --dereference-command-line follow symbolic links listed on the command line --dereference-command-line-symlink-to-dir follow each command line symbolic link that points to a directory --hide=PATTERN do not list implied entries matching shell PATTERN (overridden by -a or -A) --indicator-style=WORD append indicator with style WORD to entry names: none (default), slash (-p), file-type (--file-type), classify (-F) -i, --inode print the index number of each file -I, --ignore=PATTERN do not list implied entries matching shell PATTERN -k like --block-size=1K -l use a long listing format -L, --dereference when showing file information for a symbolic link, show information for the file the link references rather than for the link itself -m fill width with a comma separated list of entries -n, --numeric-uid-gid like -l, but list numeric user and group IDs -N, --literal print raw entry names (don't treat e.g. control characters specially) -o like -l, but do not list group information -p, --indicator-style=slash append / indicator to directories -q, --hide-control-chars print ? instead of non graphic characters --show-control-chars show non graphic characters as-is (default unless program is `ls' and output is a terminal) -Q, --quote-name enclose entry names in double quotes --quoting-style=WORD use quoting style WORD for entry names: literal, locale, shell, shell-always, c, escape -r, --reverse reverse order while sorting -R, --recursive list subdirectories recursively -s, --size print the allocated size of each file, in blocks -S sort by file size --sort=WORD sort by WORD instead of name: none -U, extension -X, size -S, time -t, version -v --time=WORD with -l, show time as WORD instead of modification time: atime -u, access -u, use -u, ctime -c, or status -c; use specified time as sort key if --sort=time --time-style=STYLE with -l, show times using style STYLE: full-iso, long-iso, iso, locale, +FORMAT. FORMAT is interpreted like `date'; if FORMAT is FORMAT1<newline>FORMAT2, FORMAT1 applies to non-recent files and FORMAT2 to recent files; if STYLE is prefixed with `posix-', STYLE takes effect only outside the POSIX locale -t sort by modification time -T, --tabsize=COLS assume tab stops at each COLS instead of 8 -u with -lt: sort by, and show, access time with -l: show access time and sort by name otherwise: sort by access time -U do not sort; list entries in directory order -v natural sort of (version) numbers within text -w, --width=COLS assume screen width instead of current value -x list entries by lines instead of by columns -X sort alphabetically by entry extension -1 list one file per line SELinux options: --lcontext Display security context. Enable -l. Lines will probably be too wide for most displays. -Z, --context Display security context so it fits on most displays. Displays only mode, user, group, security context and file name. --scontext Display only security context and file name. --help display this help and exit --version output version information and exit SIZE may be (or may be an integer optionally followed by) one of following: KB 1000, K 1024, MB 1000*1000, M 1024*1024, and so on for G, T, P, E, Z, Y. Using color to distinguish file types is disabled both by default and with --color=never. With --color=auto, ls emits color codes only when standard output is connected to a terminal. The LS_COLORS environment variable can change the settings. Use the dircolors command to set it. Exit status: 0 if OK, 1 if minor problems (e.g., cannot access subdirectory), 2 if serious trouble (e.g., cannot access command-line argument). Report ls bugs to [email protected] GNU coreutils home page: <http://www.gnu.org/software/coreutils/> General help using GNU software: <http://www.gnu.org/gethelp/> For complete documentation, run: info coreutils 'ls invocation' $ cd --help Usage: cd [ options ] [directory] Or: cd [ options ] old new OPTIONS -L Handle each pathname component .. in a logical fashion by moving up one level by name in the present working directory. -P The present working directory is first converted to an absolute pathname that does not contain symbolic link components and symbolic name components are expanded in the resulting directory name.
ls -d command in linux
$ ls -d
.
If used with -d option it will not show the contents of directory.While
with -D it will display contents.
$ ls -D
1 cgroup etc InMageAgent4516 InMageAgent6561 media opt sbin
tmp var apps core.20311 export InMageAgent5529 lib misc proc
selinux tmp_install bin dbdumps home InMageAgent5536 lib64
mnt root srv tools boot dev InMageAgent5540 lost+found net
samba-test sys usr
whatis command in linux with examples
$whatis usage: whatis keyword ... $whatis ls ls (1) - list directory contents ls (1p) - list directory contents $whatis cat cat (1) - concatenate files and print on the standard output cat (1p) - concatenate and print files rraiop@dc2nix2d223$whatis ls ls (1) - list directory contents ls (1p) - list directory contents
man command in linux
There is another very good option to take help for any commands in linux is the man command in Linux. These are called man pages in the linux world. syntax of man command in linux is as below.
$ man mkdir MKDIR(1) User Commands MKDIR(1) NAME mkdir - make directories SYNOPSIS mkdir [OPTION]... DIRECTORY... DESCRIPTION Create the DIRECTORY(ies), if they do not already exist. Mandatory arguments to long options are mandatory for short options too. -m, --mode=MODE set file mode (as in chmod), not a=rwx - umask -p, --parents no error if existing, make parent directories as needed -v, --verbose print a message for each created directory -Z, --context=CTX set the SELinux security context of each created directory to CTX When COREUTILS_CHILD_DEFAULT_ACLS environment variable is set, -p/p --parents option respects default umask and ACLs, as it does in Red Hat Enterprise Linux 7 by default. --help display this help and exit --version output version information and exit.
That`s it about how to use help command in Linux. I guess you will find all related options like help, man,whatis, and –help options with any commands handy while navigating through shell/bash prompt.
Conclusion
Linux is the leading operating system that is ruling and keeps evolving day by day as it is open source. The range of Linux commands and associated switches are too vast. Once you start exploring you will come to know new options with each linux command and many other helping linux commands.
