Shell Getting Started Tutorial: Process Control (6) while loop

Syntax for While loop:

While condition test
Do
Command Area
Done

Example:

#!/bin/bashdeclare-i i=1declare-i Sum=0while ((i<=10)) Dolet Sum+=ilet ++idoneecho $sum

Use while to read file contents

While loop, the classic usage is to go with the switch input, read the contents of the file, as follows:

#!/bin/bashwhile Read Linedoecho $linedone < Cvsfile

• Line 3, use read to read the data from the standard input, put into the variable lines, if the read data is not empty, enter the loop.
• Line 6, the contents of the Cvsfile to the input, to read reading.

One more example:

#!/bin/bashifs= ': ' While read F1 F2 F3 f4 f5 f6 f7doecho ' account: $f 1,login Shell Yes: $f 7 "Done <"/etc/passwd "

Line 3, read/etc/passwd each line account data, and put the fields into the variable F1~F7.

While Infinite loop

Whlie ((1)) Doecho ' Sleepless ' done

It is also possible to change ((1)) to [1].

Or:

Whlie truedoecho ' Night sleepless ' done

Or:

Whlie:d oecho ' Night sleepless ' done

Type CTRL + C to terminate the loop.

Shell Getting Started Tutorial: Process Control (6) while loop