Shell Scripts



Command Line Arguments
command
 arg1
 arg2
 arg3
 arg4
 arg5
 arg6
 arg7
 arg8
 arg9
$0
 $1
 $2
 $3
 $4
 $5
 $6
 $7
 $8
 $9

$#
 the number of command line arguments
$*
 all the command line arguments i.e. echo "$*" => echo "$1 $2..."
$@
 all the command line arguments i.e. echo "$@" => echo "$1" "$2"...
shift
 promotes each argument one position to the left

Debugging (+flag = on -flag = off)
-x
 print ech line just before it executes
-v
 prints the input lines as they are read
-n
 reads commands but does not execute them
-u
 teats unset variables as an error when substituting

Test Command
$ test expression or
$ [ expression ]
-r file
 true if file exists and is readable
-w file
 true if file exists and is writable
-x file
 true if file exists and is executable
-f file
 true if file exists and is a regular file
-d file
 true if file exists and is a directory
-c file
 true if file exists and is a character special file
-b file
 true if file exists and is a block special file
-p file
 true if file exists and is a named pipe special file
-u file
 true if file exists and has set-user-id bit set
-g file
 true if file exists and has set-group-id bit set
-k file
 true if file exists and has sticky bit set
-s file
 true if file exists and has a size greater than zero
-t [filedes]
 true if the open file in slot fildes (file descriptor) is associated with a terminal
-z s1
 true if the length of string s1 is zero
-n s1
 true if the length of string s1 is non-zero
s1 = s2
 true if strings s1 and s2 are identical
s1 != s2
 true if strings s1 and s2 are not identical
s1
 true if s1 is not the null string
n1 -eq n2
 true if the integers n1 and n2 are algebraically equal
-lt less than
-le less than or equal
-gt greater than
-ge greater than or equal
-ne not equal
-eq equal
!
 negation
-a
 binary and
-o
 binary or (-a has higher precedence)
(expression)
 parentheses for grouping

Control Structure
if then else
 if commands_to_test; then
commands
else
commands
fi
if then elif
 if commands_to_test; then
commands
elif commands_to_test; then
commands
else
commands
fi
for in loop
 for loop_index in arg_list; do
commands
done
while loop
 while commands_to_test; do
commands
done
until loop
 until commands_to_test; do
commands
done
break (for, while, until)
 transfers control immediately to the expression after the nearest done
continue (for, while, until)
 bring execution to top of loop
case statement
 case test-string in
pattern-1) commands-1
;;
pattern-2) commands-2
;;
pattern-3) commands-3
;;
esac

Page Created May 31st, 2004