Fedora Linux

$#	Number of arguments from the script's command line	If $# is 0, then no options were given on the command line.
$* $@	All of the arguments from the script's command line	When quoted, '$*' becomes a single block of text containing all of the arguments, while '$@' becomes separate words. If the script is called with the arguments 'green' and 'yellow', then '$*' would evaluate to 'green yellow', while '$@' would evaluate to 'green' 'yellow'.
$?	Exit status of the last command	Manpages document the possible exit-status values for most commands.

4.12.1.3. Control structures

Like most programming languages, bash features a number of control structures to enable looping and conditional execution. The three most common control structures are listed in Table 4-18 ; there is also a C-style for loop that I'll discuss in the next section.

Table 4-18. Common bash control structures

Structure	Notes	Example
for variable in list	The variable is assigned the first value in list, and loop-commands are executed. The process is then repeated for all of the other values in list.	# Set X to 'hosts', then display the filename and file contents. Repeat for 'services'
do		for X in hosts services
loop-commands		do
done		echo '==== $X'
		cat /etc/$X
		done
if control-command	If the control-command succeeds, the if-commands are executed; otherwise, the else-commands are executed.	# Tell the user if the text 'test' appears in file1
then		if grep -q test file1
if-commands		then
[else		echo 'Found it!'
else-commands]		else
fi		echo 'Not found.'
		fi
while control-command	As long as control-command executes successfully, loop-commands are repeated.	# Display the free disk space every 2 seconds, forever
do		while sleep 2