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Reading, writing and substring operations in Shell Script

Posted on 2003-10-21
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Last Modified: 2013-12-13
I am new to shell scripts so please excuse my newbie questions or mistakes

1) How do i read a file into a shell script variable.?  While reading i should preserve all special characters, tabs, carriage returns etc, ineffect everything that is there in that file should be kept as is.  A text file needs to be created by this script which will further be processed by a Java program.

2) Once i read the file, i need to check if the first 2 characters are **.

3) How do i write to a new file everytime the script is executed.  The name is not very important.

Thank you all for your help
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Question by:ns11
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sunnycoder earned 100 total points
ID: 9597572
>How do i read a file into a shell script variable.?  
for i in `cat filename`
or you can use
cat filename | while read line

>While reading i should preserve all special characters, tabs, carriage returns etc, ineffect everything that is there
>in that file should be kept as is.
first method I listed will not preserve newlines and other formatting while second one will

whether you should preserve them or not depends on your application needs

>A text file needs to be created by this script which will further be processed by a Java program.
why not use cp if you are simply copying it !!

>2) Once i read the file, i need to check if the first 2 characters are **.
use grep ^** or sed if you wish to replace them ... more details will be helpful

>3) How do i write to a new file everytime the script is executed.  The name is not very important.
a simple way could be to keep a count in a file ... increment this count everytime you write to a newfile
generate name as
newfile.<count from file>
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by:sunnycoder
ID: 9604807
>3) How do i write to a new file everytime the script is executed.  The name is not very important.
for this purpose, you can also use mktemp ... man mktemp

any feedback ?
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by:Skytzo
ID: 9745345

There are two powerful utilties that you can use.

Sed and Awk.   I advise you to go to google and do a search on shell scripting tutorial and simply walk through the step by step guides that you find.

Second, go to google and do a search on Sed and Awk tutorial and work through those.

What you are trying to achieve is relatively simple, and could probably get what you need within a few hours of going through the tutorials.

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