Back-End Programming Exam > Back-End Programming Videos > Shell Scripting: Discovering to Automate Command-Line Tasks > Shell Scripting Tutorial-41: The 'for' Loop
Shell Scripting Tutorial-41: The 'for' Loop Video Lecture | Shell Scripting: Discovering to Automate Command-Line Tasks - Back-End Programming
FAQs on Shell Scripting Tutorial-41: The 'for' Loop Video Lecture - Shell Scripting: Discovering to Automate Command-Line Tasks - Back-End Programming
| 1. What is a 'for' loop in shell scripting? |  |
Ans. A 'for' loop in shell scripting is a control flow statement that allows us to execute a set of commands repeatedly, based on a sequence of values or a list of items. It iterates over each item in the list and performs the specified commands for each item.
| 2. How do you define a 'for' loop in shell scripting? | |
Ans. In shell scripting, a 'for' loop is defined using the following syntax:
```
for variable in list
do
commands
done
```
Here, the `variable` takes each value from the `list`, and the `commands` within the loop are executed for each value.
| 3. Can we use a 'for' loop to iterate over a range of numbers in shell scripting? | |
Ans. Yes, we can use a 'for' loop to iterate over a range of numbers in shell scripting. This can be achieved by using the `seq` command and command substitution. Here's an example:
```
for i in $(seq 1 5)
do
echo "Number: $i"
done
```
In this example, the loop will iterate over the numbers 1 to 5 and print each number.
| 4. How can we iterate over items in an array using a 'for' loop in shell scripting? | |
Ans. To iterate over items in an array using a 'for' loop in shell scripting, we can use the following syntax:
```
array=("item1" "item2" "item3")
for item in "${array[@]}"
do
echo "Item: $item"
done
```
Here, the `array[@]` expands to all the elements in the array, and the loop iterates over each item in the array, printing it.
| 5. Is it possible to use a 'for' loop to iterate over files in a directory? | |
Ans. Yes, it is possible to use a 'for' loop to iterate over files in a directory. We can use the wildcard character (*) to specify the files we want to iterate over. Here's an example:
```
for file in /path/to/directory/*
do
echo "File: $file"
done
```
In this example, the loop will iterate over all the files in the specified directory and print each file's name.
Text Transcript from Video
hello guys my name is mother and welcome
to my channel this is the forty first
tutorial in the series of tutorials on
UNIX shell scripting in this tutorial
we're going to learn to use the for loop
now Paul is pretty different from while
and untell and in the last editorial the
script files that we made we knew in
advance the number of times we wanted to
execute the new blocks right we wanted
to display ten numbers so we initialized
our control variable to one and we kept
on incrementing it till it got the value
will happen and that's how we got our
numbers on screen but four offers a
better syntax and a better mechanism in
cases where you do not know in advance
how many times you want the loop to
execute right so you know I'll just
demonstrate the loop for you in a script
and you'll be able to understand it so I
have my text editor here and I've saved
this file in the home folder give me the
name for in the extension SH and I'm not
gonna put a comment in the script
because it doesn't really make any sense
to just type in for loop in action of
course you people know that for loops
gonna be a nationalist way so I'll just
get started and I type in the keyword
for on the first line and then I'll type
in my control variable right and I'm not
going to call it count this time instead
I'm gonna give it the name item and what
this script is going to do is it's gonna
scan through the home folder
and it will check for dietary files
right so basically it will check for the
folders in the home folder and it will
display the names of all the folders in
the you know as the output on the screen
right so I'll show you the condition of
the home folder first so I have a bunch
of diet freezer desktop for example is
the diet free documents is that free
downloads directory and I have diet
freeze tool videos and after videos I
have all these executable script files
like Ford or SS will file in SS 9 an
assister we do all these our script
files right so what the script we do is
it will scan through the home folder and
by that I mean it will you know go
through each and every item in the home
folder and we'll check ok
is desktop that free
of course it is so display its name in
the output and documents is a folder yes
so display its name but for door SH or
SS 9 or SS these are not deities so
these names will not be displayed on
screen so that's what the script is
gonna do it's gonna be a pretty simple
script but we're not going to use LS so
you know let's just see how it's going
to work so I have my control variable
and I've given it the name icon and
after the control variable I'm going to
type in the keyword in and - and on the
next line I'll type in done and all my
for loop statements are gonna go between
do and done but how many times or you
know how do I want four to decide what
it has to do I'll have to give it some
target folder name or you know I'll have
to tell a you know where it has to
search for the items and that I'm going
to do by putting an asterisk symbol
after the keyword in and if you guys
remember when I discussed LS with you in
maybe the twelve or thirteen tutorial I
told you that the significance of
asterisk
when you use it you know with LS is that
it stands for everything in the current
directory right and since the for script
is saved in the home folder astrick when
the shell will execute the for door SH
file would mean all the items in the
home folder right so I hope you get that
and between the due and done keywords I
will have to check if the current item
is a diet free or not and that I'm going
to do by using if statement and we'll
square brackets output the condition -
Dean space hyphen D space dollar item
right and well if the item is a diet
free then we will have to echo its name
out so put mean then and Fi I'll type in
echo dollar item fi now save this file
and let me first execute it for you and
then I'll talk you guys to respect
so I said space over the word research
now
press the Enter key you see that I only
get the names of the folders and not the
files right so let me talk you guys
through your script once again for item
in star what this would do is I would
get each and every you know I to Lucy in
the home folder that is in the first
titration item will get the desktop
folder and it will check if desktop is
that fee or not and of course it is so
it will be displayed and this will keep
on happening till we get to videos but
when the loop counter reaches poor dot
SS it will check whether forward Sh is a
directory or not by executing this test
condition that you have on line three
and it's not a diet tree so you know
this would be skipped and then SS nine
door sh will be assigned to item and the
same procedure will be followed and this
will keep on happening till all the
items in the home folder have been
exhausted right so if for example here
in my output I don't want to see the
dike trees but if I want to see the
files all I have to do is make a very
little change in the test condition in
my if statement I'll have to put hyphen
F instead of - D right so I save the
file and let me clear the screen first
and when I execute the script you see
that this time I don't see my folder
names I just see my you know file names
so that's it that's how you use the for
loop and as I mentioned earlier in this
tutorial for is a better option than
while and unti in cases when you do not
know how many times you have to execute
the loop for example in this case we
don't we don't know how many items we
had in the home folder right I mean I
would have had to check first
by executing LS or by opening the home
folder and seeing at the bottom here
that it has 20 items but that was you
know it's too much word so that's why I
use 4 and also since this is the first
time we have our variable in the script
I haven't used a dollar symbol here
right and
you don't have to do that you don't
necessarily have to initialize your
control variable if you're using four so
for item space in space Astrix symbol
and asterisk as I mentioned earlier
stands for all the items that you have
in the home for you so that's it for now
and in the next tutorial we're gonna
check out something interesting maybe an
application if these loops but from the
time being that's all I wanted to talk
about so thank you so much for watching
this tutorial
and please subscribe to my channel
to my channel this is the forty first
tutorial in the series of tutorials on
UNIX shell scripting in this tutorial
we're going to learn to use the for loop
now Paul is pretty different from while
and untell and in the last editorial the
script files that we made we knew in
advance the number of times we wanted to
execute the new blocks right we wanted
to display ten numbers so we initialized
our control variable to one and we kept
on incrementing it till it got the value
will happen and that's how we got our
numbers on screen but four offers a
better syntax and a better mechanism in
cases where you do not know in advance
how many times you want the loop to
execute right so you know I'll just
demonstrate the loop for you in a script
and you'll be able to understand it so I
have my text editor here and I've saved
this file in the home folder give me the
name for in the extension SH and I'm not
gonna put a comment in the script
because it doesn't really make any sense
to just type in for loop in action of
course you people know that for loops
gonna be a nationalist way so I'll just
get started and I type in the keyword
for on the first line and then I'll type
in my control variable right and I'm not
going to call it count this time instead
I'm gonna give it the name item and what
this script is going to do is it's gonna
scan through the home folder
and it will check for dietary files
right so basically it will check for the
folders in the home folder and it will
display the names of all the folders in
the you know as the output on the screen
right so I'll show you the condition of
the home folder first so I have a bunch
of diet freezer desktop for example is
the diet free documents is that free
downloads directory and I have diet
freeze tool videos and after videos I
have all these executable script files
like Ford or SS will file in SS 9 an
assister we do all these our script
files right so what the script we do is
it will scan through the home folder and
by that I mean it will you know go
through each and every item in the home
folder and we'll check ok
is desktop that free
of course it is so display its name in
the output and documents is a folder yes
so display its name but for door SH or
SS 9 or SS these are not deities so
these names will not be displayed on
screen so that's what the script is
gonna do it's gonna be a pretty simple
script but we're not going to use LS so
you know let's just see how it's going
to work so I have my control variable
and I've given it the name icon and
after the control variable I'm going to
type in the keyword in and - and on the
next line I'll type in done and all my
for loop statements are gonna go between
do and done but how many times or you
know how do I want four to decide what
it has to do I'll have to give it some
target folder name or you know I'll have
to tell a you know where it has to
search for the items and that I'm going
to do by putting an asterisk symbol
after the keyword in and if you guys
remember when I discussed LS with you in
maybe the twelve or thirteen tutorial I
told you that the significance of
asterisk
when you use it you know with LS is that
it stands for everything in the current
directory right and since the for script
is saved in the home folder astrick when
the shell will execute the for door SH
file would mean all the items in the
home folder right so I hope you get that
and between the due and done keywords I
will have to check if the current item
is a diet free or not and that I'm going
to do by using if statement and we'll
square brackets output the condition -
Dean space hyphen D space dollar item
right and well if the item is a diet
free then we will have to echo its name
out so put mean then and Fi I'll type in
echo dollar item fi now save this file
and let me first execute it for you and
then I'll talk you guys to respect
so I said space over the word research
now
press the Enter key you see that I only
get the names of the folders and not the
files right so let me talk you guys
through your script once again for item
in star what this would do is I would
get each and every you know I to Lucy in
the home folder that is in the first
titration item will get the desktop
folder and it will check if desktop is
that fee or not and of course it is so
it will be displayed and this will keep
on happening till we get to videos but
when the loop counter reaches poor dot
SS it will check whether forward Sh is a
directory or not by executing this test
condition that you have on line three
and it's not a diet tree so you know
this would be skipped and then SS nine
door sh will be assigned to item and the
same procedure will be followed and this
will keep on happening till all the
items in the home folder have been
exhausted right so if for example here
in my output I don't want to see the
dike trees but if I want to see the
files all I have to do is make a very
little change in the test condition in
my if statement I'll have to put hyphen
F instead of - D right so I save the
file and let me clear the screen first
and when I execute the script you see
that this time I don't see my folder
names I just see my you know file names
so that's it that's how you use the for
loop and as I mentioned earlier in this
tutorial for is a better option than
while and unti in cases when you do not
know how many times you have to execute
the loop for example in this case we
don't we don't know how many items we
had in the home folder right I mean I
would have had to check first
by executing LS or by opening the home
folder and seeing at the bottom here
that it has 20 items but that was you
know it's too much word so that's why I
use 4 and also since this is the first
time we have our variable in the script
I haven't used a dollar symbol here
right and
you don't have to do that you don't
necessarily have to initialize your
control variable if you're using four so
for item space in space Astrix symbol
and asterisk as I mentioned earlier
stands for all the items that you have
in the home for you so that's it for now
and in the next tutorial we're gonna
check out something interesting maybe an
application if these loops but from the
time being that's all I wanted to talk
about so thank you so much for watching
this tutorial
and please subscribe to my channel
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Oct 24, 2024 Last updated |
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