unix utilities

awk :

1. To get selected fields from file

$ cat file

Name:No:E-mail
abc1:1:abc1@gmail.com
abc2:2:abc2@gmail.com
abc3:3:abc3@gmail.com
abc4:4:abc4gmail.com



$  cat file | awk -F: '{ print $1 "  " print$2  }'

it prints Name   and No

$cat file | awk -F: '{ print $3  }'

It prints All the E-mails 


Foreach :


1. Print all the files 

foreach i ( `ls` )

    echo $i 

end

2.  Executive some script on all html files 

foreach i ( `ls *.html` )

    update_the_file.pl $1 

end

sed:

1. Replace old_str to new_str in files 

$ sed -i 's/old_str/new_str/g'   test.txt 

2. Replace in multiple files using shell  

#!/bin/bash
     for fl  in *.html;  do
     mv $fl $fl.old
     sed 's/FINDSTRING/REPLACESTRING/g' $fl.old > $fl
     rm -f $fl.old
     done

3. -i extension
Edit files in-place, saving backups with the specified extension.

e.g 

$ ls greetings.txt $ cat greetings.txt hello hi there $ sed -i .original 's/hello/bonjour/' greetings.txt $ ls greetings.txt greetings.txt.bak $ cat greetings.txt bonjour hi there $ cat greetings.txt.original hello hi there



perl one-liner :

1. Replace old_str with new_str 

$perl -0777 -e 's/old_str/new_str/g'


2. Replace multiple lines with multiple lines 

$ cat  alpha.txt
This is
a test
Please do not
be alarmed

$ perl -0777 -i.original -pe 's/a test\nPlease do not/not a test\nBe/igs' alpha.txt

$ diff alpha.txt alpha.txt.original

2,3c2,3
< not a test
< Be
---
> a test
> Please do not

3. get the info same as awk 

To get selected fields from file

$ cat file

Name:No:E-mail
abc1:1:abc1@gmail.com
abc2:2:abc2@gmail.com
abc3:3:abc3@gmail.com
abc4:4:abc4gmail.com



$  cat file | perl -F: -lane  'print  F[0] "  " F[1] '

it prints Name   and No

$cat file | perl -F: -lane  'print  F[2] '

It prints All the E-mails