All the Unix commands come with a number of optional and mandatory options. It is very common to forget the complete syntax of these commands.
Because no one can possibly remember every Unix command and all its options, we have online help available to mitigate this right from when Unix was at its development stage.
Unix’s version of Help files are called man pages. If there is a command name and you are not sure how to use it, then Man Pages help you out with every step.
Syntax
Here is the simple command that helps you get the detail of any Unix command while working with the system −
$man command
Example
Suppose there is a command that requires you to get help; assume that you want to know about pwd then you simply need to use the following command −
$man pwd
The above command helps you with the complete information about the pwd command. Try it yourself at your command prompt to get more detail.
You can get complete detail on man command itself using the following command −
$man man
Man Page Sections
Man pages are generally divided into sections, which generally vary by the man page author’s preference. Following table lists some common sections −
| Sr.No. | Section & Description |
|---|---|
| 1 | NAME Name of the command |
| 2 | SYNOPSIS General usage parameters of the command |
| 3 | DESCRIPTION Describes what the command does |
| 4 | OPTIONS Describes all the arguments or options to the command |
| 5 | SEE ALSO Lists other commands that are directly related to the command in the man page or closely resemble its functionality |
| 6 | BUGS Explains any known issues or bugs that exist with the command or its output |
| 7 | EXAMPLES Common usage examples that give the reader an idea of how the command can be used |
| 8 | AUTHORS The author of the man page/command |
To sum it up, man pages are a vital resource and the first avenue of research when you need information about commands or files in a Unix system.
Useful Shell Commands
The following link gives you a list of the most important and very frequently used Unix Shell commands.
If you do not know how to use any command, then use man page to get complete detail about the command.
Here is the list of Unix Shell – Useful Commands
This quick guide lists commands, including a syntax and a brief description. For more detail, use −
$man command
Files and Directories
These commands allow you to create directories and handle files.
| Sr.No. | Command & Description |
|---|---|
| 1 | cat Displays File Contents |
| 2 | cd Changes Directory to dirname |
| 3 | chgrp Changes file group |
| 4 | chmod Changes permissions |
| 5 | cp Copies source file into destination |
| 6 | file Determines file type |
| 7 | find Finds files |
| 8 | grep Searches files for regular expressions |
| 9 | head Displays first few lines of a file |
| 10 | ln Creates softlink on oldname |
| 11 | ls Displays information about file type |
| 12 | mkdir Creates a new directory dirname |
| 13 | more Displays data in paginated form |
| 14 | mv Moves (Renames) an oldname to newname |
| 15 | pwd Prints current working directory |
| 16 | rm Removes (Deletes) filename |
| 17 | rmdir Deletes an existing directory provided it is empty |
| 18 | tail Prints last few lines in a file |
| 19 | touch Updates access and modification time of a file |
Manipulating data
The contents of files can be compared and altered with the following commands.
| Sr.No. | Command & Description |
|---|---|
| 1 | awk Pattern scanning and processing language |
| 2 | cmp Compares the contents of two files |
| 3 | comm Compares sorted data |
| 4 | cut Cuts out selected fields of each line of a file |
| 5 | diff Differential file comparator |
| 6 | expand Expands tabs to spaces |
| 7 | join Joins files on some common field |
| 8 | perl Data manipulation language |
| 9 | sed Stream text editor |
| 10 | sort Sorts file data |
| 11 | split Splits file into smaller files |
| 12 | tr Translates characters |
| 13 | uniq Reports repeated lines in a file |
| 14 | wc Counts words, lines, and characters |
| 15 | vi Opens vi text editor |
| 16 | vim Opens vim text editor |
| 17 | fmt Simple text formatter |
| 18 | spell Checks text for spelling error |
| 19 | ispell Checks text for spelling error |
| 20 | emacs GNU project Emacs |
| 21 | ex, edit Line editor |
| 22 | emacs GNU project Emacs |
Compressed Files
Files may be compressed to save space. Compressed files can be created and examined.
| Sr.No. | Command & Description |
|---|---|
| 1 | compress Compresses files |
| 2 | gunzip Helps uncompress gzipped files |
| 3 | gzip GNU alternative compression method |
| 4 | uncompress Helps uncompress files |
| 5 | unzip List, test and extract compressed files in a ZIP archive |
| 6 | zcat Cat a compressed file |
| 7 | zcmp Compares compressed files |
| 8 | zdiff Compares compressed files |
| 9 | zmore File perusal filter for crt viewing of compressed text |
Getting Information
Various Unix manuals and documentation are available on-line. The following Shell commands give information −
| Sr.No. | Command & Description |
|---|---|
| 1 | apropos Locates commands by keyword lookup |
| 2 | info Displays command information pages online |
| 2 | man Displays manual pages online |
| 3 | whatis Searches the whatis database for complete words |
| 4 | yelp GNOME help viewer |
Network Communication
These following commands are used to send and receive files from a local Unix hosts to the remote host around the world.
| Sr.No. | Command & Description |
|---|---|
| 1 | ftp File transfer program |
| 2 | rcp Remote file copy |
| 3 | rlogin Remote login to a Unix host |
| 4 | rsh Remote shell |
| 5 | tftp Trivial file transfer program |
| 6 | telnet Makes terminal connection to another host |
| 7 | ssh Secures shell terminal or command connection |
| 8 | scp Secures shell remote file copy |
| 9 | sftp Secures shell file transfer program |
Some of these commands may be restricted at your computer for security reasons.
Messages between Users
The Unix systems support on-screen messages to other users and world-wide electronic mail −
| Sr.No. | Command & Description |
|---|---|
| 1 | evolution GUI mail handling tool on Linux |
| 2 | mail Simple send or read mail program |
| 3 | mesg Permits or denies messages |
| 4 | parcel Sends files to another user |
| 5 | pine Vdu-based mail utility |
| 6 | talk Talks to another user |
| 7 | write Writes message to another user |
Programming Utilities
The following programming tools and languages are available based on what you have installed on your Unix.
| Sr.No. | Command & Description |
|---|---|
| 1 | dbx Sun debugger |
| 2 | gdb GNU debugger |
| 3 | make Maintains program groups and compile programs |
| 4 | nm Prints program’s name list |
| 5 | size Prints program’s sizes |
| 6 | strip Removes symbol table and relocation bits |
| 7 | cb C program beautifier |
| 8 | cc ANSI C compiler for Suns SPARC systems |
| 9 | ctrace C program debugger |
| 10 | gcc GNU ANSI C Compiler |
| 11 | indent Indent and format C program source |
| 12 | bc Interactive arithmetic language processor |
| 13 | gcl GNU Common Lisp |
| 14 | perl General purpose language |
| 15 | php Web page embedded language |
| 16 | py Python language interpreter |
| 17 | asp Web page embedded language |
| 18 | CC C++ compiler for Suns SPARC systems |
| 19 | g++ GNU C++ Compiler |
| 20 | javac JAVA compiler |
| 21 | appletvieweir JAVA applet viewer |
| 22 | netbeans Java integrated development environment on Linux |
| 23 | sqlplus Runs the Oracle SQL interpreter |
| 24 | sqlldr Runs the Oracle SQL data loader |
| 25 | mysql Runs the mysql SQL interpreter |
Misc Commands
These commands list or alter information about the system −
| Sr.No. | Command & Description |
|---|---|
| 1 | chfn Changes your finger information |
| 2 | chgrp Changes the group ownership of a file |
| 3 | chown Changes owner |
| 4 | date Prints the date |
| 5 | determin Automatically finds terminal type |
| 6 | du Prints amount of disk usage |
| 7 | echo Echo arguments to the standard options |
| 8 | exit Quits the system |
| 9 | finger Prints information about logged-in users |
| 10 | groupadd Creates a user group |
| 11 | groups Show group memberships |
| 12 | homequota Shows quota and file usage |
| 13 | iostat Reports I/O statistics |
| 14 | kill Sends a signal to a process |
| 15 | last Shows last logins of users |
| 16 | logout Logs off Unix |
| 17 | lun Lists user names or login ID |
| 18 | netstat Shows network status |
| 19 | passwd Changes user password |
| 20 | passwd Changes your login password |
| 21 | printenv Displays value of a shell variable |
| 22 | ps Displays the status of current processes |
| 23 | ps Prints process status statistics |
| 24 | quota -v Displays disk usage and limits |
| 25 | reset Resets terminal mode |
| 26 | script Keeps script of terminal session |
| 27 | script Saves the output of a command or process |
| 28 | setenv Sets environment variables |
| 30 | stty Sets terminal options |
| 31 | time Helps time a command |
| 32 | top Displays all system processes |
| 33 | tset Sets terminal mode |
| 34 | tty Prints current terminal name |
| 35 | umask Show the permissions that are given to view files by default |
| 36 | uname Displays name of the current system |
| 37 | uptime Gets the system up time |
| 38 | useradd Creates a user account |
| 39 | users Prints names of logged in users |
| 40 | vmstat Reports virtual memory statistics |
| 41 | w Shows what logged in users are doing |
| 42 | who Lists logged in users |
