CODEWITHSUNDEEP
bashsed
Village
Village

Reputation: 24463

Delete all lines beginning with a # from a file

All of the lines with comments in a file begin with #. How can I delete all of the lines (and only those lines) which begin with #? Other lines containing #, but not at the beginning of the line should be ignored.

Upvotes: 280

Views: 320667

Answers (10)

ata
ata

Reputation: 2065

The opposite of Raymond's solution:

sed -n '/^#/!p'

"don't print anything, except for lines that DON'T start with #"

Upvotes: 22

Asclepius
Asclepius

Reputation: 63536

This answer builds upon the earlier answer by Keith.

grep -Ev "^[[:blank:]]*#" should filter out comment lines.

grep -Ev "^[[:blank:]]*(#|$)" should filter out both comments and empty lines, as is frequently useful.

For information about [:blank:] and other character classes, refer to https://en.wikipedia.org/wiki/Regular_expression#Character_classes.

Upvotes: 8

Aditya Aggarwal
Aditya Aggarwal

Reputation: 680

If you want to delete from the file starting with a specific word, then do this:

grep -v '^pattern' currentFileName > newFileName && mv newFileName currentFileName

So we have removed all the lines starting with a pattern, writing the content into a new file, and then copy the content back into the source/current file.

Upvotes: 1

محسن عباسی
محسن عباسی

Reputation: 2454

Delete all empty lines and also all lines starting with a # after any spaces:

sed -E '/^$|^\s*#/d' inputfile

For example, see the following 3 deleted lines (including just line numbers!):

1. # first comment
2.
3.         # second comment

After testing the command above, you can use option -i to edit the input file in place.

Just this!

Upvotes: 0

Ahmed Khaled
Ahmed Khaled

Reputation: 124

You also might want to remove empty lines as well

sed -E '/(^$|^#)/d' inputfile

Upvotes: 4

Raymond Hettinger
Raymond Hettinger

Reputation: 226754

This can be done with a sed one-liner:

sed '/^#/d'

This says, "find all lines that start with # and delete them, leaving everything else."

Upvotes: 460

rubo77
rubo77

Reputation: 20885

you can directly edit your file with

sed -i '/^#/ d'

If you want also delete comment lines that start with some whitespace use

sed -i '/^\s*#/ d'

Usually, you want to keep the first line of your script, if it is a sha-bang, so sed should not delete lines starting with #!. also it should delete lines, that just contain only a hash but no text. put it all together:

sed -i '/^\s*\(#[^!].*\|#$\)/d'

To be conform with all sed variants you need to add a backup extension to the -i option:

sed -i.bak '/^\s*#/ d' $file
rm -Rf $file.bak

Upvotes: 14

Bruno Damas
Bruno Damas

Reputation: 1

Here is it with a loop for all files with some extension:

ll -ltr *.filename_extension > list.lst

for i in $(cat list.lst | awk '{ print $8 }') # validate if it is the 8 column on ls 
do
    echo $i
    sed -i '/^#/d' $i
done

Upvotes: -3

Keith Thompson
Keith Thompson

Reputation: 263647

I'm a little surprised nobody has suggested the most obvious solution:

grep -v '^#' filename

This solves the problem as stated.

But note that a common convention is for everything from a # to the end of a line to be treated as a comment:

sed 's/#.*$//' filename

though that treats, for example, a # character within a string literal as the beginning of a comment (which may or may not be relevant for your case) (and it leaves empty lines).

A line starting with arbitrary whitespace followed by # might also be treated as a comment:

grep -v '^ *#' filename

if whitespace is only spaces, or

grep -v '^[  ]#' filename

where the two spaces are actually a space followed by a literal tab character (type "control-v tab").

For all these commands, omit the filename argument to read from standard input (e.g., as part of a pipe).

Upvotes: 79

jaypal singh
jaypal singh

Reputation: 77185

You can use the following for an awk solution - 

awk '/^#/ {sub(/#.*/,"");getline;}1' inputfile

Upvotes: 8

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