Shulou(Shulou.com)06/02 Report--

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

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.