Delete all lines beginning with a from a file

Question

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

User · Answer

Here is it with a loop for all files with some extension   ll -ltr   filename extension  gt  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

User · Answer

You can use the following for an awk solution -   awk        sub           getline  1  inputfile

User · Answer

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

User · Answer

This answer builds upon the earlier answer by Keith   egrep -v      blank       should filter out comment lines   egrep -v      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

User · Answer

The opposite of Raymond s solution   sed -n       p     don t print anything  except for lines that DON T start with

User · Answer

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

User · Answer

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

[bash] Delete all lines beginning with a # from a file

Examples related to bash

Examples related to sed