Scripting for special usage of Bash programming loop statements under Linux (10)

Scripting for the special use of the while statement under the Linux Bash Program (10)

1. Loop control:

Break: Interrupts the entire loop statement, which is the statement following the execution of the script after exiting the loop

Continue: Interrupt the current cycle, advance to the next round cycle

Exit: End Script Run

2.while dead Loop, that is, when you do not know how many times the loop

Format: while:; Do

Looping statements

Done

3.while reads and assigns a value to the read variable from each line in the input redirection file

Format: while read Line;do

Looping statements

Done < path files

4. Instance Scripts

4.1. Find the user login in the/etc/passwd file is bash,uid greater than 500 of the top 3 users, and display their user name and UID

#!/bin/bash

Let I=1

While read line; Do

If [' Echo $LINE | cut-d:-f3 '-lt 500]; Then determine if the UID is less than 500

Continue

Fi

[' Echo $LINE | awk-f: ' {print $7} ' = = '/bin/bash '] && echo $LINE | Awk-f: ' {print $1$3} ' && let ++i

[$I-gt 3] && break

Done < /etc/passwd

~

4.2. Check if the willow user is logged into the system, unless you enter Q or Q to exit the script, otherwise enter the dead loop

#!/bin/bash

While :;d o

Read-p "q|  Q is Exit,other show does Willow come this system? "CHOICE

if [$CHOICE = = "Q"-o $CHOICE = = "Q"]; Then

echo "quiting this script"

Exit 3

Fi

If who | grep Willow &>/dev/null; Then

echo "Willow is loginnig the system at ' date '"

Else

echo "Willow is not comming at ' date '"

Fi

Done

This article is from the "Xavier Willow" blog, please be sure to keep this source http://willow.blog.51cto.com/6574604/1767492

Scripting for special usage of Bash programming loop statements under Linux (10)