24

Is it possible to do it in one liner?

I have an output like this:

"First line" - Description " Second line" - Description "Third line" - Description " Fourth line" - Description

This input is generated automatically.

I want to replace the first occurrence of " (quotation mark + space) with " (quotation mark) for each line. If I apply the substitution globally, it will also change every occurrence of line" - to line"-, so I was wondering if it is possible to use a sed one liner to accomplish this.

I have tried using ^ like this

sed -r ':a;N;$!ba;s/(\^\" )/\"/g'

But it's not working, it doesn't replace anything. I tried

sed -r ':a;N;$!ba;s/(^|\" )/\"/g'

and it replaces all the occurrences. I've just started to use sed, so I don't really know if I'm doing something wrong.

What am I missing here?

Improve this question
1
  • A note about labels: The command you wrote above may work in some implementations of sed, but for portability and to avoid really weird errors, you should end a given command argument after a label (if you need them at all). E.g., sed -e ':a' -e 'N;$!ba' -e 'whatever' Commented Apr 11, 2016 at 20:47

3 Answers 3

Reset to default
44

You're overthinking it. sed replaces only the first instance on a line by default (without the /g modifier), although you still want to anchor because you don;t so much want the first instance in the line as the one at the start of the line; and you usually don't need the explicit line actions you're trying to use (why?).

sed 's/^" /"/'
Improve this answer
3
  • Thanks! I thought it was necessary to explicitly declare the line actions when working on a file, read about it and just kept on using them. I really was over-thinking it, that couldn't be simpler and it does the trick :) Commented Apr 9, 2012 at 3:33
  • I'm tempted to say those commands are pretty much obsolete; it is possible to do quite complex multiline things with them, but it's not easy to do so and these days you're really better off using perl/python/ruby/whatever instead. Commented Apr 9, 2012 at 3:40
  • 3
    Completely disagree with the above comment; multi-line sed commands such as N and labels such as :a are not obsolete at all and they are portable and POSIX specified, unlike Perl/Python/Ruby/whatever. It is true however that if you find yourself needing them often, you should learn awk. Commented Apr 11, 2016 at 19:16
5

A more general answer, since I can't comment on geekosaur's answer - You wouldn't put the ^ (start of line anchor). For example, if you want to replace the first occurence of A with B, you would have

sed 's/A/B/'
Improve this answer
0

Using Perl

~$ perl -pe 's/^" /"/;' file

Using Raku (formerly known as Perl_6)

~$ raku -pe 's/^\" \s /"/;' file

Sample Input:

"First line" - Description " Second line" - Description "Third line" - Description " Fourth line" - Description

Sample Output (both code examples):

"First line" - Description "Second line" - Description "Third line" - Description "Fourth line" - Description

https://perldoc.perl.org/perlre
https://perldoc.perl.org/perltrap#Sed-Traps
https://docs.raku.org/language/regexes

Improve this answer

You must log in to answer this question.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.