Shell Scripting Tutorial for Beginners 18 - UNTIL loop Video Lecture | Complete Linux Course: Become a Linux Professional - Software Development

hey guys welcome to the next video on
shell scripting tutorial for beginners
in this video we will learn how to use
until loops in shell scripting now until
loops are almost similar to while you
but with a slight difference and the
difference we are going to see in a
moment but let's see first the syntax of
until loop so the syntax of until loop
is like this so you use the keyword
until and then in square brackets or in
double parenthesis also you give a
condition and if the condition is false
then the commands between the keyword do
and done are executed right so the
difference is in the while loop if the
condition is true then only the commands
are executed in the until loop the
condition is false then only the
commands are executed right so let's
take an example so once again for
example I want to print the value one to
ten on the terminal so I will declare a
variable and assign a value of 1 to it
and in the condition this time I want to
write here dollar n and then I will just
give it a flag GE which is greater than
or equal to right and then 10 so we want
to evaluate the condition if the value
of n is greater than or equal to 10 and
if it's not greater than or equal to 10
then it's going to echo the value of n
for example right so we will just write
like this and to increment the value of
n we can just write this notation so
just write and is equal to double
parenthesis and then n plus 1 here okay
so let's run the script and let's see
what happens so I am going to run the
script and it prints the value 1 to 9
and why it's happening here because this
condition is false
whenever we start
our script n is equal to one here right
so when this point is reached the N is
equal to 1 which is not greater 210 or
not greater than or equal to 10 so it
goes here right so it's checks for the
false condition right and then if the
condition is false which is false in
this case because n is not greater than
or equal to 10 then it prints this value
with the echo command and then increment
the value of n by this right and it goes
on and on and on until the value of n
becomes 11 which is greater than or
equal to 10 which is true
so if the condition is true this is not
executed right now if I want to print 1
to 10 I need to just write greater than
here not greater than or equal to what's
greater than right once again when I run
the script it prints 1 to 10 right
similar to a while loops you can just
use these double parentheses here to
evaluate the condition and we will just
do something like this but instead of
greater than you just need to write
something like this so until the n is
not greater than 10 then we will execute
the command so once again the values are
printed 1 to 10 right and as we have
seen we can increment the value of n in
few ways so the post increment is
possible let me clear the terminal and
once again run the script and the result
will be same and pre increment is also
possible so like this and once again run
the script and give us the similar
result okay so in this way you can use
until loop in shell scripting I hope you
enjoyed this video please recommend
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