1. Shell Loop
1.1 The while loop
Syntax:
while condition
do
Statement(s) to be executed if condition is true
done
while condition; do
Statement(s) to be executed if condition is true
done
Ex:
#!/bin/sh
a=0
while [ $a -lt 10 ]
do
echo $a
a=`expr $a + 1`
done
$./test.sh
0
1
2
3
4
5
6
7
8
9
1.2 The for loop
Syntax:
for var in word1 word2 ... wordN
do
Statement(s) to be executed for every word.
done Ex1:
#!/bin/sh
for var in 0 1 2 3 4 5 6 7 8 9
do
echo $var
done
$./test.sh
0
1
2
3
4
5
6
7
8
9
Ex2:
#!/bin/sh
for FILE in $HOME/.bash*
do
echo $FILE
done
$./test.sh
/root/.bash_history
/root/.bash_logout
/root/.bash_profile
/root/.bashrc
1.3 The until loop
Syntax:
until condition
do
Statement(s) to be executed until condition is true
done
#!/bin/sh
a=0
until [ ! $a -lt 10 ]
do
echo $a
a=`expr $a + 1`
done
$./test.sh
0
1
2
3
4
5
6
7
8
9
1.4 The select loop
Syntax:
select var in word1 word2 ... wordN
do
Statement(s) to be executed for every word.
done
Ex:
#!/bin/ksh
select DRINK in tea cofee water juice appe all none
do
case $DRINK in
tea|cofee|water|all)
echo "Go to canteen"
;;
juice|appe)
echo "Available at home"
;;
none)
break
;;
*) echo "ERROR: Invalid selection"
;;
esac
done
$./test.sh
1) tea
2) cofee
3) water
4) juice
5) appe
6) all
7) none
#? juice
Available at home
#? none
$
2. Nesting Loops (Vòng lặp lồng nhau)
Syntax:
while condition1 ; # this is loop1, the outer loop
do
Statement(s) to be executed if condition1 is true
while condition2 ; # this is loop2, the inner loop
do
Statement(s) to be executed if condition2 is true
done
Statement(s) to be executed if condition1 is true
done
Ex:
#!/bin/sh
a=0
while [ "$a" -lt 10 ] # this is loop1
do
b="$a"
while [ "$b" -ge 0 ] # this is loop2
do
echo -n "$b "
b=`expr $b - 1`
done
echo
a=`expr $a + 1`
done
$./test.sh
0
1 0
2 1 0
3 2 1 0
4 3 2 1 0
5 4 3 2 1 0
6 5 4 3 2 1 0
7 6 5 4 3 2 1 0
8 7 6 5 4 3 2 1 0
9 8 7 6 5 4 3 2 1 0