Linux while command (loop - while)

The shell has structures for testing conditions and executing certain program sequences several times (loop), until the tested condition is satisfied.

The while command on Linux continuously tests an expression until an expression has a return variable equal to zero or true.

In this example, the variable $i gains an initial value equal to zero.

As long as (while) the test command condition represented by [] returns zero (true), the loop loop will continue to execute.

In the loop, the variable $i is increased until $i reaches the condition of not being less than 4:

$ i=0
$ while [$i -lt 4]; do echo “count $i”; i=$ [$i+1]; done

count 0
count 1
count 2
count 3

The while must have a satisfied exit condition, otherwise it will be in an infinite loop.

If you what to know another form of doing loops in the shell, look the “for” command.