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Shell Scripting Tutorial for Beginners 17 - Read a file content in Bash Video Lecture | Complete Linux Course: Become a Linux Professional - Software Development
FAQs on Shell Scripting Tutorial for Beginners 17 - Read a file content in Bash Video Lecture - Complete Linux Course: Become a Linux Professional - Software Development
| 1. How can I read the contents of a file in a Bash script? |  |
Ans. To read the contents of a file in a Bash script, you can use the "cat" command followed by the file name. For example, if you have a file named "example.txt" and you want to read its contents, you can use the following command:
```bash
cat example.txt
```
This will display the contents of the file on the terminal.
| 2. Can I store the contents of a file in a variable in a Bash script? | |
Ans. Yes, you can store the contents of a file in a variable in a Bash script. You can use the command substitution feature in Bash, which allows you to capture the output of a command and store it in a variable. Here's an example:
```bash
file_content=$(cat example.txt)
```
In this example, the contents of the "example.txt" file are stored in the "file_content" variable. You can then use this variable for further processing in your script.
| 3. How can I read a specific line from a file in a Bash script? | |
Ans. If you want to read a specific line from a file in a Bash script, you can use the "sed" command. The "sed" command allows you to perform text transformations, and in this case, you can use it to extract a specific line from a file. Here's an example:
```bash
line_number=3
specific_line=$(sed -n "${line_number}p" example.txt)
```
In this example, the variable "line_number" is set to 3, indicating the line number you want to read. The "sed" command with the "${line_number}p" argument will extract the specified line from the "example.txt" file and store it in the "specific_line" variable.
| 4. How can I read a file line by line in a Bash script? | |
Ans. To read a file line by line in a Bash script, you can use a while loop along with the "read" command. Here's an example:
```bash
while IFS= read -r line
do
echo "$line"
done < example.txt
```
In this example, the "while" loop will iterate over each line in the "example.txt" file. The "read" command reads each line and stores it in the "line" variable. You can then perform any operations on each line within the loop.
| 5. How can I check if a file exists before reading its contents in a Bash script? | |
Ans. To check if a file exists before reading its contents in a Bash script, you can use the "test" command with the "-f" option. Here's an example:
```bash
file_name="example.txt"
if [ -f "$file_name" ]; then
cat "$file_name"
else
echo "File does not exist"
fi
```
In this example, the "test" command with the "-f" option checks if the file specified in the "file_name" variable exists. If it does, the contents of the file are displayed using the "cat" command. If the file does not exist, an error message is displayed.
Text Transcript from Video
hey guys welcome to the next video on
shell scripting tutorial for beginners
in this video I'm going to show you how
we can read files using while loop now
there are several ways of reading files
using while loop and we are going to see
some of them
the first way of reading files using
while loop is by using input redirection
so we use this while loop skeleton and
after this keyword while we will use the
read command so just use read and then
the variable in which we want to save
the content of the file line-by-line
okay and then what we are going to do is
we will echo this variable so just write
echo and dollar P which is this variable
itself and then if you know file
redirection we use angle bracket here so
we are going to use this angle bracket
and the name of the file whatever file
you want to you know read for example I
want to read this file itself which is
my script file hello dot Sh right so I
can just write hello dot and such and
then this is going to read this file and
then this is going to go here in the
parameter P and then using this echo is
going to read it right and what is input
3 direction so input redirection is
something like this that what wherever
the pointing edge of this angle bracket
is the stream of the read content goes
to that direction so the file content
inside this hello dot FH is redirected
to this while loop right and then it is
ready using the read command and then
it's printed using the echo command
right so let's run the script and let's
see what happens and you can see it
prints the content of the file which is
our script itself now the second way off
for reading the file is to read the file
in a single variable
then print it now if you know pipes then
it's easier for you
so I'm going to just remove this things
from here and then what I'm going to do
here is I'm going to first of all use a
cat command so before this y keyword I'm
going to use cat and then whatever file
you want to read once again hello dot Sh
and then I will use this pipe symbol and
that's it so what's happening here is
whatever is the content which is read
using this cat command is like an input
for this while command right so the
content of this cat output is like an
input to this while loop and then it's
going to read it using this read command
and then it's going to print the content
of the file so once again let's run the
script and once again you can see the
same content is printed so the first way
is by using the input redirection and
second way is to you know read the file
content into one variable and then print
it now sometimes so it's hard to read
the files using these two methods and
the problem is some special characters
in the file for example line indentation
and other things so what we can do is in
the last method is we will use this read
commands once again but we will use the
ifs now iff stands for internal field
separator and it is used by the shell to
determine how to do word splitting and
that is how to recognize word boundaries
right so let's see how we can do this
using ifs so we will use the wild
keyboard here and then in capital use
ifs and then is equal to and then give a
space here so it's important to note
here is that we are not assigning the
read to ifs we are assigning
space to an ISS right so just give the
space between this equal to sign and
read the command and with this read
command we have to use - our flag here
and - our prevents the backslash escape
from being interpreted right so this
flag is going to prevent backslashes
escapes from being interpreted right and
instead of p you can also use line
because it's more descriptive of this
method and just use the line here okay
now we are going to use once again input
redirection here so use this angle
bracket and then use the filename for
example hello dot Sh okay and let's run
the script once again and let's see what
happens and you can see it's printing
the content of the file once again now
if you are confused here instead of
using space here you can just use in
single quotes and a space here like this
also and once again once again you can
run the script and the you know output
will be the same you can see here right
so you can do this also right and for
example we want to read the file which
is there in my etc' folder for example
so let's say what are the content in my
etc' folder so I'm going to just LS for
example et Cie and you can see there are
several files here and let's see if what
we want to read from here so for example
I want to read the host cons which is
here this is the host comp so let me
just cat the content of this and then we
will read this file using our while loop
so cat and then et Cie and then the
filename host comp and this is the
content of this file right so we will
just copy the path of
this file and paste it here okay
and then once again we will run the
script and then press it and you can see
the same content is printed whatever is
printed using the cat command
right so you can use these three methods
to read the file using while loop now
there are some other methods of reading
files for example using file descriptors
and that we will see in the later videos
when we will learn what our file
descriptors and other things right but
these are the basic ways of reading the
file using while loop so I hope you've
enjoyed this video please rate comment
subscribe and bye for now
shell scripting tutorial for beginners
in this video I'm going to show you how
we can read files using while loop now
there are several ways of reading files
using while loop and we are going to see
some of them
the first way of reading files using
while loop is by using input redirection
so we use this while loop skeleton and
after this keyword while we will use the
read command so just use read and then
the variable in which we want to save
the content of the file line-by-line
okay and then what we are going to do is
we will echo this variable so just write
echo and dollar P which is this variable
itself and then if you know file
redirection we use angle bracket here so
we are going to use this angle bracket
and the name of the file whatever file
you want to you know read for example I
want to read this file itself which is
my script file hello dot Sh right so I
can just write hello dot and such and
then this is going to read this file and
then this is going to go here in the
parameter P and then using this echo is
going to read it right and what is input
3 direction so input redirection is
something like this that what wherever
the pointing edge of this angle bracket
is the stream of the read content goes
to that direction so the file content
inside this hello dot FH is redirected
to this while loop right and then it is
ready using the read command and then
it's printed using the echo command
right so let's run the script and let's
see what happens and you can see it
prints the content of the file which is
our script itself now the second way off
for reading the file is to read the file
in a single variable
then print it now if you know pipes then
it's easier for you
so I'm going to just remove this things
from here and then what I'm going to do
here is I'm going to first of all use a
cat command so before this y keyword I'm
going to use cat and then whatever file
you want to read once again hello dot Sh
and then I will use this pipe symbol and
that's it so what's happening here is
whatever is the content which is read
using this cat command is like an input
for this while command right so the
content of this cat output is like an
input to this while loop and then it's
going to read it using this read command
and then it's going to print the content
of the file so once again let's run the
script and once again you can see the
same content is printed so the first way
is by using the input redirection and
second way is to you know read the file
content into one variable and then print
it now sometimes so it's hard to read
the files using these two methods and
the problem is some special characters
in the file for example line indentation
and other things so what we can do is in
the last method is we will use this read
commands once again but we will use the
ifs now iff stands for internal field
separator and it is used by the shell to
determine how to do word splitting and
that is how to recognize word boundaries
right so let's see how we can do this
using ifs so we will use the wild
keyboard here and then in capital use
ifs and then is equal to and then give a
space here so it's important to note
here is that we are not assigning the
read to ifs we are assigning
space to an ISS right so just give the
space between this equal to sign and
read the command and with this read
command we have to use - our flag here
and - our prevents the backslash escape
from being interpreted right so this
flag is going to prevent backslashes
escapes from being interpreted right and
instead of p you can also use line
because it's more descriptive of this
method and just use the line here okay
now we are going to use once again input
redirection here so use this angle
bracket and then use the filename for
example hello dot Sh okay and let's run
the script once again and let's see what
happens and you can see it's printing
the content of the file once again now
if you are confused here instead of
using space here you can just use in
single quotes and a space here like this
also and once again once again you can
run the script and the you know output
will be the same you can see here right
so you can do this also right and for
example we want to read the file which
is there in my etc' folder for example
so let's say what are the content in my
etc' folder so I'm going to just LS for
example et Cie and you can see there are
several files here and let's see if what
we want to read from here so for example
I want to read the host cons which is
here this is the host comp so let me
just cat the content of this and then we
will read this file using our while loop
so cat and then et Cie and then the
filename host comp and this is the
content of this file right so we will
just copy the path of
this file and paste it here okay
and then once again we will run the
script and then press it and you can see
the same content is printed whatever is
printed using the cat command
right so you can use these three methods
to read the file using while loop now
there are some other methods of reading
files for example using file descriptors
and that we will see in the later videos
when we will learn what our file
descriptors and other things right but
these are the basic ways of reading the
file using while loop so I hope you've
enjoyed this video please rate comment
subscribe and bye for now
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Dec 23, 2024 Last updated |
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