Syntax for basic shell script constructs

• if statement - can be used to perfroms a specific action/s based on the result of conditional expression

if [ a -eq b ]
then
.......
.......
else
........
........
fi

 

or
in one line
if [ a -eq b ]; then .......; .......; else ........; ........; fi

 

#Here ';' plays an important role. In unix ';' represents end of command line

 

ex:
$ if [ 1 = 2 ];then echo true;else echo false;fi
false

 

 

• for statement - can be used to iterate through a list of values

 

array_list="1 2 3 4 5 6 7 8 9 10"

for i in $array_list

do

echo $i

done

 

in one line

array_list="1 2 3 4 5 6 7 8 9 10"; for i in $array_list; do echo $i; done

 

ex:

$ array_list="1 2 3 4 5 6 7 8 9 10"; for i in $array_list; do echo $i; done

1

2

3

4

5

6

7

8

9

10

• while statement - can be used to read a list

any command that gives a list of values | while read a; do echo $a; done

$ ls t*|while read a; do echo $a; done
t
test
testif.ksh
tpt
try.ksh

• To replace any search word on the fly in vi editor

to replace in whole file use Esc, then type :%s/findwors/replaceword/gc
This promts for confirmation every word it find and to replace

If you want to suppress promt remove c from the above command.

from a spefic line in file to specific line number
Esc then type :10,20s/findword/replaceword