CODEWITHSUNDEEP
linuxsedgrep
Aprilian8
Aprilian8

Reputation: 434

how to make grep ignore first line and process other line

I need to remove line beginning with '#' in some txt file. but ignoring the first line as it header. how to make grep ignore first lines and remove any line beginning with # for rest of the lines?

cat sample.txt
#"EVENT",VERSION, NAME
1,2,xyz
1,2,abc
1,2,asd
1,2,ert
#"EVENT",VERSION, NAME
1,2,xyz
1,2,abc
1,2,xyz

cat sample.txt | grep -v "^\s*[#\;]\|^\s*$" > "out.txt"

but this removes the header too!

Upvotes: 4

Views: 20252

Answers (6)

raven-rock
raven-rock

Reputation: 63

Applying an arbitrary command to all but the first line - a "header" - of a file or stream of tabular data is such a common task for me that I define a helper utility called body for it:

As a shell function (put this in your ~/.bashrc or equivalent):

body() {
  IFS= read -r header
  printf '%s\n' "$header"
  "$@"
}

Now:

$ cat sample.txt | body grep -v '^#'
#"EVENT",VERSION, NAME
1,2,xyz
1,2,abc
1,2,asd
1,2,ert
1,2,xyz
1,2,abc
1,2,xyz

Credit: adapted from: Command line tools for doing data science, where it's a one of many handy data tools you can put in your shell's PATH variable. Wish many of these could be canonicalized as standard UNIX tools.

Upvotes: 2

user7712945
user7712945

Reputation:

tried on gnu sed

sed '0,/^#/n;/^#/d' sample.txt

Upvotes: 0

potong
potong

Reputation: 58371

This might work for you (GNU sed):

sed '1b;/^#/d' file

Ignore the first line and delete any other lines that start with #.

Upvotes: 2

Ed Morton
Ed Morton

Reputation: 203189

This will cause any awk to print each line if its line number is 1 or it doesn't start with #:

$ awk 'NR==1 || !/^#/' file
#"EVENT",VERSION, NAME
1,2,xyz
1,2,abc
1,2,asd
1,2,ert
1,2,xyz
1,2,abc
1,2,xyz

Upvotes: 1

Cyrus
Cyrus

Reputation: 88563

With sed:

sed '2,${/^#/d}' sample.txt

From second row (2) to last row ($): search (/.../) for rows beginning (^) with # and delete (d) them. Default action of sed is to print current row.

Output:

#"EVENT",VERSION, NAME
1,2,xyz
1,2,abc
1,2,asd
1,2,ert
1,2,xyz
1,2,abc
1,2,xyz

Upvotes: 7

zedfoxus
zedfoxus

Reputation: 37039

Try a combination of head and grep like so:

head -1 sample.txt > out.txt && grep -v "^#" sample.txt >> out.txt

Result

#"EVENT",VERSION, NAME
1,2,xyz
1,2,abc
1,2,asd
1,2,ert
1,2,xyz
1,2,abc
1,2,xyz

Alternate method

grep "^#" sample.txt | head -1 > out.txt && grep -v "^#" sample.txt >> out.txt

That is - grep lines beginning with # but just choose the first one and write it to a file. Then, grep all lines not starting with # and append those liens to the same output file.

Upvotes: 1

Related Questions