CODEWITHSUNDEEP
linux
domlao
domlao

Reputation: 16029

How to use grep to extract a line with inconsistent number of space character

Like I have a text file with,

    +
 Code here
 +
 Code here +
 Code+ here
    +
 Code here

And I want to grep this file and only show the line with a + character only? What regex should I construct?

Please advise

Many thanks

Upvotes: 0

Views: 220

Answers (2)

paxdiablo
paxdiablo

Reputation: 881463

If you want a line with nothing but the + character, use:

grep '^+$' inputFile

This uses the start and end markers to ensure it only has that one character.

However, if you want lines with only a + character, possibly surrounded by spaces (as seems to be indicated by your title), you would use something like:

grep '^ *+ *$' inputFile

The sections are:

  • "^", start of line marker.
  • " *", zero or more spaces.
  • "+", your plus sign.
  • " *", zero or more spaces.
  • "$", end of line marker.

The following transcript shows this in action:

pax> echo '    +
 Code here
 +
 Code here +
 Code+ here
    +     
 Code here' | grep '^ *+ *$' | sed -e 's/^/OUTPUT:>/' -e 's/$/</'
OUTPUT:>    +<
OUTPUT:> +<
OUTPUT:>    +     <

The input data has been slightly modified, and a sed filter has been added, to show how it handles spacing on either side.

And if you want general white space rather than just spaces, you can change the space terms from the current " *" into "\s*" for example.

Upvotes: 1

Kevin
Kevin

Reputation: 56069

If I understand correctly, you want the line with only a +, no whitespace. To do that, use ^ and $ to match the beginning and end of the line, respectively. 

grep '^+$' filename

Upvotes: 1

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