How to check command help or to find command for a term in Linux ?

In this article, we will see how to get help with a command in linux. No one can ever learn all commands of linux/UNIX, it is always suggested that you should know how to run a command in linux and for this we should know how to view help, syntax, or man pages in linux. 
 
	In Linux/UNIX, we have many command to check for help or to know how to use a command. Let us look at these ways. 
 
	1. Man Page of a command 
 
	To view the manual page for command help, just run command name followed by keryword "man". For example: 
 
	-bash-3.2$ man date 
  
	DATE(1)                          User Commands                         DATE(1)  
  
	   
  
	NAME  
  
	       date - print or set the system date and time  
  
	   
  
	SYNOPSIS  
  
	       date [OPTION]... [+FORMAT]  
  
	       date [-u|--utc|--universal] [MMDDhhmm[[CC]YY][.ss]]  
  
	   
  
	DESCRIPTION  
  
	       Display the current time in the given FORMAT, or set the system date.  
  
	   
  
	   
  
	2. Info Command  
  
	The other way to know more about command, we can use "info" command. For example:  
  
	   
  
	  
		-bash-3.2$ info date  
	  
		File: coreutils.info,  Node: date invocation,  Next: uname invocation,  Up: Sys  
	  
		tem context  
	  
		   
	  
		21.1 `date': Print or set system date and time  
	  
		==============================================  
	  
		   
	  
		Synopses:  
	  
		   
	  
		     date [OPTION]... [+FORMAT]  
	  
		     date [-u|--utc|--universal] [ MMDDhhmm[[CC]YY][.ss] ]  
	  
		   
	  
		   Invoking `date' with no FORMAT argument is equivalent to invoking it  
	  
		with a default format that depends on the `LC_TIME' locale category.  
	  
		In the default C locale, this format is `'+%a %b %e %H:%M:%S %Z %Y'',  
	  
		so the output looks like `Thu Mar  3 13:47:51 PST 2005'.  
	  
		   
  
 
	3. --help or -h argument. 
 
	"--help" argument displays help of the command syntax and it helps us to get the correct syntax of the command. Let us look at an example: 
 
	  
  
	-bash-3.2$ date -h  
  
	date: invalid option -- h  
  
	Try `date --help' for more information.  
  
	-bash-3.2$ date --help  
  
	Usage: date [OPTION]... [+FORMAT]  
  
	  or:  date [-u|--utc|--universal] [MMDDhhmm[[CC]YY][.ss]]  
  
	Display the current time in the given FORMAT, or set the system date.  
  
	   
  
	  -d, --date=STRING         display time described by STRING, not `now'  
  
	  -f, --file=DATEFILE       like --date once for each line of DATEFILE  
  
	  -r, --reference=FILE      display the last modification time of FILE  
  
	  -R, --rfc-2822            output date and time in RFC 2822 format  
  
	      --rfc-3339=TIMESPEC   output date and time in RFC 3339 format.  
  
	                            TIMESPEC=`date', `seconds', or `ns' for  
  
	                            date and time to the  
  
	   
  
	Now suppose you forget the command but you know that you want command related to term "raid" to configure raid on your computer. So we can search our man pages containing this term "raid".  
  
	   
  
	So there are two arguments with man command "-k" or "-K" i.e. in small case and in upper case. Both help us to get the required man page.  
  
	   
  
	  
		-bash-3.2$ man -K date  
	  
		/usr/kerberos/man/man8/ftpd.8.gz? [ynq] n  
	  
		/usr/kerberos/man/man8/telnetd.8.gz? [ynq] n  
	  
		/usr/kerberos/man/man8/klogind.8.gz? [ynq] n  
	  
		/usr/kerberos/man/man8/kadmin.8.gz? [ynq] n  
	  
		/usr/kerberos/man/man8/kshd.8.gz? [ynq]  
	  
		   
	  
		  
			-bash-3.2$ man -k date  
		  
			/etc/updatedb.conf [updatedb] (5)  - a configuration file for updatedb(8)  
		  
			APR::Date            (3pm)  - Perl API for APR date manipulating functions  
		  
			BN_BLINDING_update [BN_BLINDING_new] (3ssl)  - blinding related BIGNUM functions  
		  
			EVP_CipherUpdate [EVP_EncryptInit] (3ssl)  - EVP cipher routines  
		  
			EVP_DecryptUpdate [EVP_EncryptInit] (3ssl)  - EVP cipher routines  
		  
			EVP_DigestUpdate [EVP_DigestInit] (3ssl)  - EVP digest routines  
		  
			EVP_EncryptUpdate [EVP_EncryptInit] (3ssl)  - EVP cipher routines  
		  
			EVP_OpenUpdate [EVP_OpenInit] (3ssl)  - EVP envelope decryption  
		  
			EVP_SealUpdate [EVP_SealInit] (3ssl)  - EVP envelope encryption  
		  
			EVP_SignUpdate [EVP_SignInit] (3ssl)  - EVP signing functions  
		  
			EVP_VerifyUpdate [EVP_VerifyInit] (3ssl)  -   
		  
			   
		  
			So now you can easily work in linux and can able to find the help. Manual pages help a lot and you will later realise that these are very useful and you should make a habit to refer them for various argument/options provided by these.  

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