Appending a line to a file only if it does not already exist

Question

I need to add the following line to the end of a config file   include   configs projectname conf    to a file called lighttpd conf  I am looking into using sed to do this  but I can t work out how   How would I only insert it if the line doesn t already exist

User · Answer

Here s a sed version   sed -e    include   configs projectname conf  h    x s incl    g t  a   -e  include   configs projectname conf   -e     file   If your string is in a variable   string  include   configs projectname conf   sed -e     string h     x s  string    g t  a    -e   string  -e     file

User · Answer

If you want to run this command using a python script within a Linux terminal    import os sys LINE    include     lt insert line STRING gt  FILE    lt insert file path STRING gt                                  os system  grep -qxF   quot   LINE   quot    FILE      echo   quot   LINE   quot   gt  gt    FILE   The   and double quotations had me in a jungle  but this worked  Thanks everyone

User · Answer

another sed solution is to always append it on the last line and delete a pre existing one   sed -e   a   -e   lt your-entry gt   -e    lt your-entry-properly-escaped gt  d     properly-escaped  means to put a regex that matches your entry  i e  to escape all regex controls from your actual entry  i e  to put a backslash in front of            this might fail on the last line of your file or if there s no dangling newline  I m not sure  but that could be dealt with by some nifty branching

User · Answer

If  one day  someone else have to deal with this code as  legacy code   then that person will be grateful if you write a less exoteric code  such as  grep -q -F  include   configs projectname conf   lighttpd conf if      -ne 0    then   echo  include   configs projectname conf    gt  gt  lighttpd conf fi

User · Answer

I needed to edit a file with restricted write permissions so needed sudo  working from ghostdog74 s answer and using a temp file   awk  FNR  NR  amp  amp   configs  projectname  conf  f 1 next f  0 END  if  f    print  your line      file  gt   tmp file sudo mv  tmp file file

User · Answer

use awk  awk  FNR  NR  amp  amp   configs  projectname  conf  f 1 next f  0 END  if  f    print  your line      file file

User · Answer

Just keep it simple     grep   echo should suffice   grep -qxF  include   configs projectname conf   foo bar    echo  include   configs projectname conf    gt  gt  foo bar    -q be quiet -x match the whole line -F pattern is a plain string https   linux die net man 1 grep   Edit  incorporated  cerin and  thijs-wouters suggestions

User · Answer

Using sed  It will insert at the end of line  You can also pass in variables as usual of course   grep -qxF  port 9033   light conf if      -ne 0    then   sed -i    a port 9033   light conf else     echo  port 9033 already added  fi   Using oneliner sed  grep -qxF  port 9033   lightconf    sed -i    a port 9033   lightconf   Using echo may not work under root  but will work like this  But it will not let you automate things if you are looking to do it since it might ask for password   I had a problem when I was trying to edit from the root for a particular user  Just adding the  username before was a fix for me   grep -qxF  port 9033  light conf if      -ne 0    then   sudo -u  user name echo  port 9033   gt  gt  light conf else     echo  already there      fi

User · Answer

This would be a clean  readable and reusable solution using grep and echo to add a line to a file only if it doesn t already exist   LINE  include   configs projectname conf   FILE  lighttpd conf  grep -qF --   LINE    FILE     echo   LINE   gt  gt    FILE    If you need to match the whole line use grep -xqF   Add -s to ignore errors when the file does not exist  creating a new file with just that line

User · Answer

If writing to a protected file   drAlberT and  rubo77  s answers might not work for you since one can t sudo  gt  gt    A similarly simple solution  then  would be to use tee --append  or  on MacOS  tee -a    LINE  include   configs projectname conf   FILE lighttpd conf grep -qF   LINE    FILE      echo   LINE    sudo tee --append   FILE

User · Answer

The answers using grep are wrong  You need to add an -x option to match the entire line otherwise lines like  text to add will still match when looking to add exactly text to add   So the correct solution is something like   grep -qxF  include   configs projectname conf   foo bar    echo  include   configs projectname conf    gt  gt  foo bar

[linux] Appending a line to a file only if it does not already exist

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