Why does the while statement in Shell only loop once?

1. Event Description:

1 ,#! /Bin/bash

Cat ../ip.txt | while read line

Do

Echo $ line

SSH $ line "ls"

Done

The result is recycled once and then exited. The reason is that while uses the redirection mechanism. All the information in the file is read and redirected to the entire while statement. The SSH statement just reads everything in the input. After the SSH statement is called, the input cache has been read. When the read Statement is read again, it cannot read a record and exits cyclically.

2 ,#! /Bin/bash

Cat ../ip.txt | while read line

Do

Echo ------------ $ line

Ls

Done

Exit after normal Loop

#! /Bin/bash

Cat ../ip.txt | while read line

Do

Echo ------------ $ line

Cat

Done

Exit once in a loop. cat prints other records in the file.

Ii. solution:

1. Replace it with the for statement.

#! /Bin/bash

For line in 'cat ../ip.txt'

Do

Echo $ line

SSH $ line "ls"

Done

2. input redirection

#! /Bin/bash

Cat ../ip.txt | while read line

Do

Echo $ line

SSH $ line "ls" </dev/null

Done

This article is from the "linuxdream" blog, please be sure to keep this source http://books.blog.51cto.com/2600359/1554840

Why does the while statement in Shell only loop once?