get first through third char  : cut -c1-3
get third char to end of line : cut -c3-
match matt and not matthew    : grep -w matt
give count of matched lines   : grep -c matt
print lines that do NOT match : grep -v matt
print line with string match  : grep "matt baker"
print a line match            : grep ^"my name is matt"$
delete first 3 lines          : sed -e 1,3d
get rid of letter 'k'         : sed -e s/k//g
change matt to stephen        : sed -e s/matt/stephen/g
print only a line             : sed -n 1p
print a range of lines        : sed -n 5-10p
print a line based on a var   : sed -n ${CNT}p
change lower to upper case    : tr [a-z] [A-Z]
delete char                   : tr -d 's'
change tabs to newlines       : tr '\t' '\012'



NOTE: ksh (Korn) can run pure sh (and mixed sh and ksh), 
	but sh (Bourne) cannot recognize any ksh unique syntax.
	(Korn is a superset of Bourne.) 

Shell     Executeable     Prompt     Best Usage      Author
Bourne    /bin/sh         $          programming     Stephen Bourne
C-Shell   /bin/csh        %          interactive     Bill Joy
Korn      /bin/ksh        $          both            David Korn

testing
	csh: ()
	sh:  []
	ksh: [], [[]], (())
		[[]] - ascii
		(()) - integer

Input/output
	stdin
		cmd < in_file    #0
	stdout
		cmd > out_file   #1
	stderr
		cmd 2> err_file  #2

	stdout and stderr together
		DIFFERENT FILES
			cmd > out_file  2> err_file
		SAME FILES
			cmd 2>&1 out_and_err_file

	stderr only output to pipe, but not stdout
		cmd 2>&1  > /dev/null  | grep "pattern-from-stderr"
		#**OR**
		command 2> >(grep 'pattern-from-stderr') > /dev/null
		#**OR**
		command 2> >(grep -v pattern-from-stderr 1>&2)

Pipes
	cmd | cmd

Subshells
	(cmd;cmd)

test
	NOTE: The word "test" and '[' are the same.

	"test -d /tmp" **is-equivelant-to** "[[ -d /tmp ]]"

unary
	[[ -d /usr/tmp ]]

some unary tests 
	file       
		-f, 
		file is non-zero (size)
			-s
	directory
		-d
	null VAR
		-z
	non-null VAR
		-n

strings 
	[[ matt == matt ]]

integers
	(( 1 == 3 ))

loops
	for NODE in adm1 adm2 nms1 nms2
	do
		ssh $NODE df
	done

	for PART in $(df | grep ^dev | awk '{print $1}')
		rsh $NODE chpt -q $PART > /tmp/$NODE_$PART
	done

while
	#infinite loop
	while (( 1 ))
		ls; sleep 60
	done

Running a script
		ksh program_name
	or
		chmod 755 program_name
		programe_name

debug methods
	ksh -[vx] prgm

	run that section of code by itself, line-by-line
	ksh [-x] <CR>
	$ (enter commands, execute after <CR>)
	$ ^D

print (like echo)
	print "hello"
	print "$VAR at $LINENO"

style/philosophy
	put in file:
		description
		author
		date: create and modify
		os ver
		h/w type
		comment large sections of code and important and complex lines
		also comment logic areas/lines
		cleanup of files at the end of your script or trap (^C)

most problems incurred when:
	cutting and pasting (var and file names)
	syntax (done, fi, esac; using = instead of ==)
	forgot to init var
	logic errors
	non-unique filenames: 
		use $$ for PID so each file is unique 
		(so you can run multiple instances of program)

awk 
	print first field
	awk '{print $1}'

	print if match (number of fiels on line is 6, print whole line
	awk '{if (NF == 6) print $0}'

	print percentage
	awk '{s=$1 / $2 * 100; print s}'

	sum/avg/max/min
	#pick a field - number 3 in this example
	CNT=3
	echo "Max        Min        Sum         Avg"
	awk '{input = $$CNT
                {if(input >= max) max = input} \
                {if(input <= min) min = input} \
                {sum += input} END \
                {printf %6d     %6d     %6d     %8.2f\n , \
			max, min, sum, sum/NR}'

	use cut instead of awk (nor recommended) fields 1-3
		cut -f 1-3

		#colon is field separator
		cut -d: -f1-3

#
# test for alpha char
#
if [[ $proceed == *[[:alpha:]]* ]]
then
	echo "VAlue ${proceed} is invalid. Exiting......."
	exit 1
fi

#
# compile shell script
#
http://alnazmin.blogspot.com/2011/07/how-to-compile-bash-script-using-shc.html