Example of Linux Shell process control statement
Author: Cheng Mo,
www.cnblogs.com/chengmo/archive/2010/10/14/1851434.html
The Linux shell has its own set of flow control statements, including conditional statements (if), loop statements (for,while), and select statements (case). Below I will introduce the following examples, the use of each statement method.
1. Shell conditional statement (if usage)
if statement structure [if/then/elif/else/fi]
if conditional test statement
then
action
[elif conditions
action
else
action
]
fi
If you are not clear about: conditional test statements, you can refer to: linux shell logical operators, logical expressions
Shell commands can be separated by semicolons or newlines. If you want to write more than one command on a line, you can split it by "';".
[chengmo@centos5 ~]$ a=5;if [[ a -gt 4 ]] ;then echo 'ok';fi;
ok
Example: (test.sh)
#!/ bin/sh
scores=40;
if [[ $scores -gt 90 ]]; then
echo "very good! ";
elif [[ $scores -gt 80 ]]; then
echo "good! ";
elif [[ $scores -gt 60 ]]; then
echo "pass! ";
else
echo "no pass! ";
fi;
The test is: [],[],
For,while,until:
for recycling method (for/do/done)
Syntax structure:
1. for... in statements
for variable in seq string
do
action
done
Description: seq string as long as the space character division, each time for... in read, will read the value in order, to the previous variable.
Example (testfor.sh):
#!/ bin/sh
for i in $(seq 10); do
echo $i;
done;
seq 10 produces 1 2 3... 10 spaces separate strings.
2.for((assignment; condition; operation statement))
for((assignment; condition; operation statement))
do
action
done;
Example (testfor2.sh):
#!/ bin/sh
for((i=1;i
