How to parse a file using shell script

Question

I am having a file :

[email protected]
[email protected]
[email protected]
//[email protected]
//[email protected]
//[email protected]
[email protected]
[email protected]
[email protected]

I want to write a script which parse the file and for the first occurrence of say abc@gmail it should remain as it is and for other occurrence if "//" found then ok otherwise add "//" at the starting of all other occurrence.

It's not entirely clear to me what you wish to achieve. Can you provide sample output (the result you aim with this input). — willeM_ Van Onsem
– willeM_ Van Onsem, Commented May 26, 2015 at 17:17
S/he wants to comment out all lines that were seen before, unless already commented out. — Jens
– Jens, Commented May 26, 2015 at 17:20
sample output: [email protected] [email protected] [email protected] //[email protected] //[email protected] //[email protected] //[email protected] //[email protected] //[email protected] — Abhinav
– Abhinav, Commented May 26, 2015 at 17:22

anubhava · Accepted Answer · 2015-05-26 17:21:32Z

2

You can use this awk command:

awk '$1 in seen && !/^[[:blank:]]*\/\// { $0 = "//" $0 } !seen[$1]++{} 1' file
[email protected]
[email protected]
[email protected]
//[email protected]
//[email protected]
//[email protected]
//[email protected]
//[email protected]
//[email protected]

answered May 26, 2015 at 17:21

anubhava

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2 Comments

Abhinav Over a year ago

thanks anubhava ..... i would request you to help me in learning shell script i know a few basics but for complex things i just need google or platform like stackoverflow... could you please suggest any tutorials or books which i can refer...Thank you so much..

anubhava Over a year ago

I just search good tutorials online. Start with this one

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