BASH/C3/Using-File-Descriptors/English - Revision history

Nancyvarkey at 05:31, 6 September 2014

2014-09-06T05:31:17Z

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Ashwini at 12:12, 5 September 2014

2014-09-05T12:12:27Z

Ashwini at 12:10, 5 September 2014

2014-09-05T12:10:36Z

Ashwini: Created page with "'''Title of script: Using file descriptors ''' '''Author:''' Lavitha Pereira and Ashwini Patil '''Keywords: Video tutorial, file descriptors to file, closing file descript..."

2014-09-04T07:47:32Z

Created page with "'''Title of script: Using file descriptors ''' '''Author:''' Lavitha Pereira and Ashwini Patil '''Keywords: Video tutorial, file descriptors to file, closing file descript..."

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'''Title of script: Using file descriptors '''

'''Author:''' Lavitha Pereira and Ashwini Patil

'''Keywords: Video tutorial, file descriptors to file, closing file descriptors'''

{| style="border-spacing:0;"
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| <center>Visual Cue</center>
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| <center>Narration</center>

|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 1
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Dear friends, Welcome to the spoken tutorial on''' Using file descriptors'''

|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 2
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| In this tutorial, we will learn aboutto

* Assign an output file descriptor
* Assign an imput file descriptor
* Closeing the file descriptor (fd)
* With the help of some examples

|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 3'''Prerequisites'''

| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| To follow this tutorial you should have knowledge of '''Shell Scripting''' in''' BASH.'''

If not, for relevant tutorials please visit our website which is as shown,'''(http://www.spoken-tutorial.org)'''

|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 4

'''System requirements'''
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| For this tutorial I am using''' '''

* '''Ubuntu Linux''' 12.04''' '''Operating System and
* '''GNU BASH''' version 4.2

Please note,''' GNU Bash''' '''version 4''' or above is recommended to practice this tutorial.

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Introduction

Slide 5
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let us start with an introduction.

We have already studied about the '''file descriptors''' in the previous tutorial.

* 0, 1 and 2 are the standard file descriptors for''' stdin,''' '''stdout''' and '''stderr.'''
* File descriptors are used to improve the reading and writing performance.I doubt it. This depends on a file type/file size. We should specifically state what kind of performance?(read write to disk/buffer). Else it is sufficient to say that 'File descriptors are i/o redirections.' This can be the second point. Not needed
* File descriptors are used for i/o redirection

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Slide 6

Is this showed on slide?''Reply to Lavitha (11/08/2014, 12:17): "..."''

Yes

Syntax:

'''<nowiki>exec [File descriptor] > filename</nowiki>'''
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| SThe syntax to assign a '''file descriptor '''to an output file is:

'''<nowiki>exec [File descriptor] > filename</nowiki>'''

Let us see an example.

I have a code file with the name '''fdassign.sh'''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| <nowiki>#!/usr/bin/env bash </nowiki>
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The first line is the '''shebang line.'''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| exec 3> output.txt

| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The '''exec''' command replaces the current '''shell process'''.

It will be executed in the place of the current '''shell '''without creating a new process.

We know that 0, 1, and 2 are standard '''file descriptors. '''

For any newly opened file, we have additional '''file descriptors''' from 3 to 9.

Here, '''3 '''is the '''file descriptor'''.

This will write the output to '''output.txt''' file.

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| echo "Welcome to BASH learning" >&3

| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The string '''"Welcome to BASH learning" '''is sent to the file '''output.txt'''

This is done via a '''file descriptor 3'''.

This is similar to redirecting a string to a file.

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| date >&3

| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Each new string will be appended to the file.

For example:

We will append the current system date to the''' output.txt''' file.

The syntax is:

'''date SPACE a greater-than sign followed by ampersand followed by a file descriptor 3'''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| <nowiki>exec 3<&-</nowiki>
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Here we close the '''file descriptor'''.

After this line the '''descriptor '''cannot write anything to the '''output.txt''' file.

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''CTRL+ALT+T''' keys
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let us execute the code and see the output.

Open the '''temrinal '''using '''CTRL+ALT+T''' keys.

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Type:

'''chmod +x fdassign.sh'''

'''./fdassign'''
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Type:

'''chmod +x fdassign.sh'''

'''./fdassign'''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''cat output.txt'''
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let us check the output now by typing.-

Type:

'''cat output.txt'''

We can see that the string,

'''Welcome to BASH learning and the current system date is displayed.'''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Type:

'''echo “Hi” > &3'''
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let us go back to the editor.

Now I will type '''echo '''at the end, after the '''descriptor '''is closed.

Type:

'''echo “Hi” > &3'''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"|
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let us execute the script once again and see what happens.

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''./fdassign'''
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| On the '''terminal''',

Ppress the uparrow key, to recall the previous command

'''./fdassign'''

Now press '''Enter.'''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''./fdassign.sh: line 6: 3: Bad file descriptor'''
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| We see an error

'''./fdassign.sh: line 6: 3: Bad file descriptor'''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''Cut'''

'''echo "hiii" >&3'''

'''Paste above '''
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let us fix theis error.

Come back to the editor.

Now

I will cut the last line of code and paste it below the '''date command'''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''./fdassign.sh'''
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Click on Save.

Let us execute the code once again.

On the terminal, recall the previous command:

'''./fdassign.sh'''

and press '''Enter.'''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''cat output.txt'''
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Now let us open the '''output.txt file'''.

Type:

'''cat output.txt'''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Welcome to BASH learning

Fri Aug 8 15:02:51 IST 2014

Hi
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| We can see the output.

The string '''Hi '''is displayed at the end.

<nowiki><<PAUSE>></nowiki>

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"|
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Now we will assign the file descriptor to the input file.

Let us see an example.

I have a file named '''fdread.sh'''

Let us go through it.

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| <nowiki>[Highlight]</nowiki>

<nowiki>exec 3< output.txt </nowiki>

<nowiki>cat <&3 </nowiki>

<nowiki>exec 3<&-</nowiki>
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| This is the '''exec command.'''

Here we will read the file '''output.txt'''

The line

'''<nowiki>exec 3< output.txt</nowiki>'''

will open the file for reading.

'''cat command''' will display the content of the file.

And finally we close the '''file descriptor.'''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''chmod +x fdread.sh'''

'''./fdread.sh'''
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Now let us execute this shell script. the command.

On the terminal type:

'''chmod +x fdread.sh'''

'''./fdread.sh'''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Welcome to BASH learning

Fri Aug 8 15:12:06 IST 2014

Hi
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| We can see the output on the '''terminal'''.

The content of '''output.txt''' file is displayed.

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"|
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| This brings us to the end of this tutorial.

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Summary slide 7
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Come back to the slides.

Let us summarize

In this tutorial we learnt to,

* Assign the output file descriptor

* Assign the input file descriptor
* Closing the file descriptor.

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Assignment Slide 8
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| As an assignment,

Try to

* append a few lines to a file '''test.txt'''<br/> using '''file descriptors '''covered in this tutorial.
* Display the content of the file using '''file descriptors'''

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 9

http://spoken-tutorial.org /What\_is\_a\_Spoken\_Tutorial

About the Spoken Tutorial Project
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Watch the video available at the link shown below.

It summarises the Spoken Tutorial project.

If you do not have good bandwidth, you can download and watch it.

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 10

Spoken Tutorial Workshops
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The Spoken Tutorial Project Team

* Conducts workshops using spoken tutorials
* Gives certificates to those who pass an online test

For more details, please write to

contact@spoken-tutorial.org

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 11

Acknowledgement
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Spoken Tutorial Project is a part of the Talk to a Teacher project.

It is supported by the National Mission on Education through ICT, MHRD, Government of India.

More information on this Mission is available at: http://spoken-tutorial.org\NMEICT-Intro

|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 12
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The script has been contributed by FOSSEE and Spoken-Tutorial teams.

This is Ashwini from IIT Bombay.

Thank you for joining.

|}

@@ Line 26: / Line 26: @@
 |-
-| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 3'''Prerequisites'''
+| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 3
-−
-−
 | style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| To follow this tutorial you should have knowledge of '''Shell Scripting''' in''' BASH.'''

@@ Line 16: / Line 16: @@
 |-
 | style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide 2
-| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| In this tutorial, we will learn aboutto
+| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| In this tutorial, we will learn to
 * Assign an output file descriptor
 * Assign an imput file descriptor
-* Closeing the file descriptor (fd)
+* Close the file descriptor (fd)
 * With the help of some examples
@@ Line 53: / Line 53: @@
 We have already studied about the '''file descriptors''' in the previous tutorial.
-* 0, 1 and 2 are the standard file descriptors for''' stdin,''' '''stdout''' and '''stderr.'''
+* 0, 1 and 2 are the standard file descriptors for''' stdin,''' '''stdout''' and '''stderr'''
-* File descriptors are used to improve the reading and writing performance.I doubt it. This depends on a file type/file size. We should specifically state what kind of performance?(read write to disk/buffer). Else it is sufficient to say that 'File descriptors are i/o redirections.' This can be the second point. Not needed
 * File descriptors are used for i/o redirection
@@ Line 61: / Line 60: @@
 |-
 | style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Slide 6
 Syntax:
 '''<nowiki>exec [File descriptor] > filename</nowiki>'''
-| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| SThe syntax to assign a '''file descriptor '''to an output file is:
+| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The syntax to assign a '''file descriptor '''to an output file is:
 '''<nowiki>exec [File descriptor] > filename</nowiki>'''
@@ Line 78: / Line 72: @@
 I have a code file with the name '''fdassign.sh'''
@@ Line 105: / Line 97: @@
 This will write the output to '''output.txt''' file.
@@ Line 120: / Line 110: @@
 This is similar to redirecting a string to a file.
 |-
@@ Line 140: / Line 127: @@
 '''date SPACE a greater-than sign followed by ampersand followed by a file descriptor 3'''
@@ Line 198: / Line 183: @@
 |-
 | style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"|
-| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let us execute the script once again and see what happens.
+| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"|Click on Save. Let us execute the script once again and see what happens.
 |-
@@ Line 204: / Line 189: @@
 | style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| On the '''terminal''',
-Ppress the uparrow key, to recall the previous command
+Press the uparrow key, to recall the previous command
 '''./fdassign'''
-Now press '''Enter.'''
+press '''Enter.'''
 |-
@@ Line 223: / Line 208: @@
 '''Paste above '''
-| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let us fix theis error.
+| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let us fix this error.
@@ Line 245: / Line 230: @@
-and press '''Enter.'''
+press '''Enter.'''
 |-
@@ Line 314: / Line 299: @@
 '''./fdread.sh'''
-| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Now let us execute this shell script. the command.
+| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Now let us execute this shell script.
@@ Line 322: / Line 307: @@
 '''./fdread.sh'''

BASH/C3/Using-File-Descriptors/English - Revision history

Nancyvarkey at 05:31, 6 September 2014

Ashwini at 12:12, 5 September 2014

Ashwini at 12:10, 5 September 2014

Ashwini: Created page with "'''­Title of script: Using file descriptors ''' '''Author:''' Lavitha Pereira and Ashwini Patil '''Keywords: Video tutorial, file descriptors to file, closing file descript..."

Ashwini: Created page with "'''Title of script: Using file descriptors ''' '''Author:''' Lavitha Pereira and Ashwini Patil '''Keywords: Video tutorial, file descriptors to file, closing file descript..."