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up vote 2 down vote favorite
1

Say there is a text file as below: 

Hello world
types=""
Mario
types="Game"

All I want to do is find the first occurrence of type="" and append with word program

My desired output: 

Hello world
types="program"
Mario
types="Game"

I Need to use in Unix shell scripting.

What I tried:

sed -i  '1,/types=\"\"/s/types=\"\"/types=\"program\"/' filename

This command only inserting and not appending. Tried adding a\ but still not working.

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3 Answers 3

up vote 2 down vote accepted

POSIXly:

$ sed -e '1,/types=""/{
  //s/"/&program/
}
' file

It's strange that above fail on GNU sed, you need:

$ sed -e '1,/types=""/{
  /types=""/s/"/&program/
}
' file

All above fail if types="" appear at the first line. In that case, you can use GNU sed or BSD sed 0,/pattern/:

$ sed -e '0,/types=""/{                
  /types=""/s/"/&program/
}
' file

or POSIX one:

$ sed -e '/types=""/{
  s/"/&program/
  :1
  n
  b1
}
' file

or see @mikeserv's answer.

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I get this error {sed: -e expression #1, char 0: no previous regular expression} –  VRVigneshwara 2 days ago
    
@VRVigneshwara: What's your sed version? you need to use the second if you use GNU sed. –  cuonglm 2 days ago
1  
1,/types=""/ doesn't work if types="" is on the first line (that is, sed starts looking for types="" from the second line, and thus you get the first two types="" replaced). A solution is to use 0,/types=""/, but the 0 address is not accepted by all seds. It's ok for GNU sed, and for *BSD sed though. –  lcd047 2 days ago
    
@lcd047: Good point. Updated! –  cuonglm 2 days ago
    
@cuonglm Last one aced it ! but it's printing below after executing the command . How can it be avoided? –  VRVigneshwara yesterday
up vote 3 down vote 
{   sed '/types=""/!b
        s/"/&program/;q'
    cat
}   <infile >outfile

A POSIX sed will leave its input file offset exactly where it quits input. With GNU sed you might need the -u option, though.

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up vote 3 down vote

You can use i to insert, then d to delete the line, and q to quit:

~$ sed '/types=""/{i\
> types="program"
> d;q}' f
Hello world
types="program"
Mario
types="Game"

The following doesn't work (thanks @mikeserv): or simply c to change the line, and q to quit:

~$ sed '/types=""/{c\
> types="program"
> q}' f
Hello world
types="program"
Mario
types="Game"

(and of course keep the -i for in place)

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