Shell has the facilities
for writing programs. It has the programming constructs to perform logical
operations.
Conditions on numbers:
-gt greater than
-ge greater than or equal to
-lt less than
-le less than or equal to
-eq equal to
-ne not equal to
conditions on strings
> greater than
< less than
= equal to
!= not equal to
-z zero length
-n non-zero length
conditions on files:
-r readable file
-w writable file
-x executable file
-s file exists and not empty
-f ordinary file
-d directory
-l symbolic link
1.if
if [ condition ]
then
statements
fi
if [ condition ]
then
statements
else
statements
fi
if [ condition ]
then
statements
elif [ condition ]
then
statements
fi
2. while:
while [ condition ]
do
statements
done
3. until
until [ condition ]
do
statements
done
4. for
for variable in list
do
statements
done
5. arithmetic for:
for (svalue; evalue;
incr/decree)
do
statements
done
6. case
case “value” in
pattern 1 ) statements
break;;
patter 2 ) statements
break;;
* ) statements
break;;
esac
7. select
select name in list
do
statements
done
Arrays:
We can arrays using shell.
The subscripting will start from 0 to six hundred billion.
Ex:
K=1
While [ $k –lt 10 ]
do
read val[$k]
let k++
done
k=1
while [ $k –lt 10 ]
do
printf “{val[$k]}\n”}
let k++
done
functions:
function abc {
shell commands
return (optional)
}
A local statement inside a
function definition makes the variables involved all become local to that
function.
Function abc {
local a
shell commands
}
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