While loop in shell programming

While Syntax:

While [condition]

Do

Command

........

Done

Special while usage:

① While true | while ;;

Do

Done ---------------------- endless loop

② While read line_value

Do

Done </path_to/file ------------- each time a row is retrieved from the file and assigned to line_value.

Exercise:

Use the while statement to capture bash users in/etc/passwd.

#! /Bin/bash
#
While read line
Do
Echo $ line | cut-d:-f1, 7 | grep "bash" &>/dev/null
If [$? -Eq0]
Then
Echo 'echo $ line | cut-d:-f1, 7 | grep "bash" | cut-d:-f1'
Fi
Done </etc/passwd

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