How to replace an entire line in a text file by line number

Question

I have a situation where I want a bash script to replace an entire line in a file  The line number is always the same  so that can be a hard-coded variable   I m not trying to replace some sub-string in that line  I just want to replace that line entirely with a new line   Are there any bash methods for doing this  or something simple that can be thrown into a  sh script

User · Accepted Answer

Not the greatest  but this should work   sed -i  Ns    replacement-line   file txt   where N should be replaced by your target line number  This replaces the line in the original file  To save the changed text in a different file  drop the -i option   sed  Ns    replacement-line   file txt  gt  new file txt

User · Answer

Let s suppose you want to replace line 4 with the text  different    You can use AWK like so   awk    if  NR    4  print  different   else print  0   input file txt  gt  output file txt   AWK considers the input to be  records  divided into  fields    By default  one line is one record   NR is the number of records seen    0 represents the current complete record  while  1 is the first field from the record and so on  by default the fields are words from the line    So  if the current line number is 4  print the string  different  but otherwise print the line unchanged   In AWK  program code enclosed in     runs once on each input record   You need to quote the AWK program in single-quotes to keep the shell from trying to interpret things like the  0   EDIT  A shorter and more elegant AWK program from  chepner in the comments below   awk  NR  4   0  different     print    input file txt   Only for record  i e  line  number 4  replace the whole record with the string  different    Then for every input record  print the record   Clearly my AWK skills are rusty   Thank you   chepner   EDIT  and see also an even shorter version from  Dennis Williamson   awk  NR  4   0  different   1  input file txt   How this works is explained in the comments  the 1 always evaluates true  so the associated code block always runs   But there is no associated code block  which means AWK does its default action of just printing the whole line   AWK is designed to allow terse programs like this

User · Answer

Replace the line of the given line number with the given replacement in the given file  function replace-line-in-file         local file   1      local line num   2      local replacement   3         Escape backslash  forward slash and ampersand for use as a sed replacement      replacement escaped    echo   replacement    sed -e  s     amp      amp  g         sed -i    line num s     replacement escaped     file

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Given this test file  test txt   Lorem ipsum dolor sit amet  consectetur adipiscing elit   Duis eu diam non tortor laoreet  bibendum vitae et tellus    the following command will replace the first line to  newline text     sed  1 c   gt  newline text  test txt   Result   newline text consectetur adipiscing elit   Duis eu diam non tortor laoreet  bibendum vitae et tellus    more information can be found here   http   www thegeekstuff com 2009 11 unix-sed-tutorial-append-insert-replace-and-count-file-lines

User · Answer

in bash  replace N M by the line numbers and xxx yyy by what you want  i 1 while read line do   if  i  N   then     echo  xxx    elif  i  M   then     echo  yyy    else     echo   line    fi     i     done   lt  orig-file  gt  new-file   EDIT  In fact in this solution there are some problems  with characters   0    t  and        t   can be solve by putting IFS  before read       at end of line with -r  IFS  read -r line   but for   0   the variable is truncated  there is no a solution in pure bash    Assign string containing null-character   0  to a variable in Bash But in normal text file there is no nul character  0  perl would be a better choice  perl -ne  if     N  print xxx n  elsif     M  print yyy n  else print    lt  orig-file  gt  new-file

User · Answer

Excellent answer from Chepner  It is working for me in bash Shell      To update replace the new line string value with the exiting line of the file  MyFile  tmp ps checkdb flag    sed -i    index s      newLine     MyFile    here          index - Line no          newLine - new line string which we want to replace    Similarly below code is used to read a particular line in the file  This won t affect the actual file   LineString  sed   index d   MyFile     here           d - will delete the lines other than line no  index         So we will get the output as line string of no  index in the file

User · Answer

On mac I used  sed -i    -e  s text-on-line-to-be-changed   text-to-replace-the whole-line   file-name

User · Answer

I actually used this script to replace a line of code in the cron file on our company s UNIX servers awhile back  We executed it as normal shell script and had no problems    Create temporary file with new line in place cat  dir file   sed -e  s the original line the new line    gt   dir temp file  Copy the new file over the original file mv  dir temp file  dir file   This doesn t go by line number  but you can easily switch to a line number based system by putting the line number before the s  and placing a wildcard in place of the original line

User · Answer

You can even pass parameters to the sed command   test sh     bin bash echo  - gt  start  for i in   seq 5   do     passing parameters to sed   j     i 3     sed -i    j s    replaced by   i     output dat done echo  - gt  finished  exit    orignial output dat   a b c d e f g h i j   Executing   test sh gives the new output dat  a b c replaced by  1   replaced by  2   replaced by  3   replaced by  4   replaced by  5   i j

[bash] How to replace an entire line in a text file by line number

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