Difference between revisions of "BASH/C3/Here-document-and-Here-string/English"

• special-purpose redirection called Here documents and Here strings
• With the help of some examples

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

System requirements

• Ubuntu Linux 12.04 Operating System and
• GNU BASH version 4.2

Please note, GNU Bash version 4 or above is recommended for practice.

Here documents

• It is a special-purpose block of text or code.
• It is a form of I/O redirect.
• It feeds a command list to an interactive program or command line.
• It can be treated as a separate file.
• It can also be treated as multiple line input redirected to a shell script.

Syntax:

command << HERE

text1

text2

textN

HERE

command space less than less than space HERE.

After this on the next line, we can give the text inputs.

It can consist of any number of lines.

Here, text1, text2, textN are the text inputs.

After the text inputs, on the next line, we type the keyword HERE again.

It denotes the closing of HERE document.

I will open a file named here.sh

Welcome

to Bash

learning

HERE

wc -w << HERE

Welcome

to

Bash

learning

HERE

• wc represents 'word count'
• wc hyphen w counts the number of words in the Here document.

• The block of text until the second occurance of HERE, will be treated as a file.
• The content present in HERE document is an input to the command wc -w

If we try to execute the same command in the terminal, we should get '4' as an output.

This is because we have passed four words to the command 'wc -c'.

Now click on Save to save the file.

chmod +x here.sh>>Press Enter

dot slash here.sh>>Press Enter

Press Enter.

Type dot slash here dot sh

Press Enter.

'Output'4

That is, number of words in Here document is 4.

Hello

and

before Welcome

Let us add two more words here at the beginning of the text.

Type Hello and welcome to Bash learning

Let us execute the program again.

Press Enter.

<<PAUSE>>

Let me open a file named hereoutput.sh

It’s not necessary that you always have to use the delimiter HERE.

You can use any other delimiter also.

The 0th (zeroeth) argument, by default, is the filename.

On the terminal type:

chmod space +x space hereoutput.sh

./hereoutput.sh Sunday Monday

0'th argument is: ./hereoutput.sh which is the filename.

1st argument is: Sunday

2nd argument is: Monday

Here String

• Here string is used for input redirection from text or a variable.
• The input is mentioned in the same line within single quotes.

Syntax:

command <<< 'string'

command space three less than symbols space within single quotes write string

I will open the same file here.sh

wc space hyphen w three less than symbols space within quotes Welcome to Bash learning

This will redirect the string within quotes to the command wc -w.

Click on Save to save the changes.

./here.sh

Output

6

4

Number of words in here document is 6 and number of words in here string is 4.

Summary

Let us summarise.

In this tutorial we learnt about

• HERE document
• HERE string

Assignment

• Here document
• Here string

Hint: tr a-z A-Z.

This is the command to convert characters from lower to upper case.

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

About the Spoken Tutorial Project

It summarises the Spoken Tutorial project.

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

Spoken Tutorial Workshops

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

For more details, please write to

contact@spoken-tutorial.org

Acknowledgement

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

This is Ashwini from IIT Bombay.

Thank you for joining.