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Linux command to find and replace occurance of more than two equal sign with "==" from XML file.


 
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Operating Systems Linux Linux command to find and replace occurance of more than two equal sign with "==" from XML file.
# 1  
Old 06-21-2012
Data Linux command to find and replace occurance of more than two equal sign with "==" from XML file.

Please help me, wasted hrsSmilie, to find this soulution:-
I need a command that will work on file (xml) and replace multiple occurrence (more than 2 times)

Examples

1. '==='

2. '===='

3. '======='

should be replaced by just '=='
Note :- single character should be replaced. (= should be replaced by ==)

I have used this command:-
Code:
sed 's/==*/==/g' example.xml > example.xml

But after using this command i found, where single character = is there, it changes into ==
Below are two for examples:-


Before:-
Code:
1) <namespace key="109" case="first-letter">Book talk</namespace>
2) st        = ''[[Sleeping Murder]]'' 
| cause       =


After:-
Code:
1) <namespace key=="109" case=="first-letter">Book talk</namespace>
2) st        == ''[[Sleeping Murder]]'' 
| cause       ==

Please help,
Regards,
Red.

Moderator's Comments:
Mod Comment edit by bakunin: Please use CODE-tags when posting code or terminal output.

Corrected typo in thread title.

Last edited by bakunin; 06-21-2012 at 09:58 AM..
# 2  
Old 06-21-2012
Quote:
Originally Posted by RedRocks!!
I need a command that will work on file (xml) and replace multiple occurrence (more than 2 times)

should be replaced by just '=='
Note :- single character should be replaced. (= should be replaced by ==)

I have used this command:-
Code:
sed 's/==*/==/g' example.xml > example.xml

But after using this command i found, where single character = is there, it changes into ==
Seems to me that this is what you wanted, isn't it?

If you only want to replace two or more occurences of "=" use:

Code:
sed 's/===*/==/g' example.xml > example.xml.result

You cannot direct the output of sed to the input file, because that would overwrite and destroy the input file after the first line. Therefore a different output file name.

I hope this helps.

bakunin
This User Gave Thanks to bakunin For This Post:
# 3  
Old 06-21-2012
Thanks you so much bakunin :)

Is there any possibility, that after editing original file, and after process completes, can we replace original with output file, Becoz i have a file of 38 Gb.
I have managed shell script, as i am doing shell scripting first time, i am trying to create a script where file should be deleted after completing the process.

I want to extend command and delete original file and name the new file created same as old one.

Ex.
Code:
 sed 's/===*/==/g' inputfile.xml > outputfile.xml && COMMAND_FOR_DELETING_OLD_FILE && \
COMMAND_FOR_RENAMING_NEW_FILE_TO_SAME_AS_OLD_FILE

-Red.
(Becoz which i am working is 38 Gb and my Server dont have much resources, right command will help me.)
Moderator's Comments:
Mod Comment Please use next time code tags for your code and data

Last edited by vbe; 06-22-2012 at 01:06 PM.. Reason: code tags please!
# 4  
Old 06-23-2012
There is no other way than what you have already found out: use a different file and then move the new file over the old file.

The reason for this i have described here and in some other postings too - i don't want to repeat it.

Btw., a suggestion: stay away from GNU-seds "-i" switch: it will just make your script less portable, but will do nothing else than do the "mv"-operation automatically afterwards.

I hope this helps.

bakunin
# 5  
Old 06-24-2012
I got another command which is working Great !!

Hello,

Thank you for your suggestion. I have used, Below command, where it gives output in same file.

Code:
perl -i -pe's/===*/==/g' Example.xml

Once again thank you for helping Smilie

-Red
# 6  
Old 06-24-2012
Quote:
Originally Posted by RedRocks!!
Thank you for your suggestion. I have used, Below command, where it gives output in same file.
You seem to have misunderstood what i explained. "perl -i" does the same as "sed -i": it creates a temporary second file where it stores the changes and moves this over the original file as the last step.

You gain nothing by using perl (save for a considerably slower speed of execution, because native UNIX commands are way faster).

The point is simple: to edit a file you need to be able to store 2 versions of it.*) There is no way around that. The "-i" options of various tools just blur that fact by hiding this temporary file, but it is still necessary.

If you fear a long execution time for moving the file: don't. It is in fact just a change in the files i-node (which is a few bytes) as long as the temporary file and the original file are on the same filesystem. To execute

Code:
mv /path/to/fileA /path/to/fileB

takes the same time, regardless of the size of this file (as long as they both are on the same filesystem). So set your "TMP" or "TMPDIR" variable accordingly and have enough room on your disk - some 100GB should not really be a problem these times of multi-TB SAN storage fabrics.

I hope this helps.

bakunin

________________

*) actually this is not completely true, because there is a trick:

Code:
(cat /path/to/file) | sed '<somecommand>' > /path/to/file

This will work for files which are small enough to fit into memory. The downside is, that if anything goes wrong (power loss, reboot, process aborted, ...) your data will be irrevocably destroyed. You sure do not want to use this hack on critical data just to save a few GB of (temporary) diskspace.

Last edited by bakunin; 06-24-2012 at 07:51 PM..
# 7  
Old 06-24-2012
Quote:
Originally Posted by bakunin
... because there is a trick:

Code:
(cat /path/to/file) | sed '<somecommand>' > /path/to/file

This will work for files which are small enough to fit into memory. The downside is, that if anything goes wrong (power loss, reboot, process aborted, ...) your data will be irrevocably destroyed. You sure do not want to use this hack on critical data just to save a few GB of (temporary) diskspace.
That won't work even when there's just a single byte in the file, if the shell first creates the sed portion of the pipeline. There are no guarantees on which component of a pipeline will be created first.

Regards,
Alister

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