How to use sed to replace only the first occurrence in a file

Question

I would like to update a large number of C   source files with an extra include directive before any existing  includes  For this sort of task  I normally use a small bash script with sed to re-write the file    How do I get sed to replace just the first occurrence of a string in a file rather than replacing every occurrence   If I use  sed s  include  include  newfile h  n include    it replaces all  includes    Alternative suggestions to achieve the same thing are also welcome

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I know this is an old post but I had a solution that I used to use:

grep -E -m 1 -n 'old' file | sed 's/:.*$//' - | sed 's/$/s\/old\/new\//' - | sed -f - file

Basically use grep to print the first occurrence and stop there. Additionally print line number ie 5:line. Pipe that into sed and remove the : and anything after so you are just left with a line number. Pipe that into sed which adds s/.*/replace to the end number, which results in a 1 line script which is piped into the last sed to run as a script on the file.

so if regex = #include and replace = blah and the first occurrence grep finds is on line 5 then the data piped to the last sed would be 5s/.*/blah/.

Works even if first occurrence is on the first line.

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bin sed -f 1    include           include i   include  newfile h      How this script works  For lines between 1 and the first  include  after line 1   if the line starts with  include  then prepend the specified line   However  if the first  include is in line 1  then both line 1 and the next subsequent  include will have the line prepended  If you are using GNU sed  it has an extension where 0    include   instead of 1   will do the right thing

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Quite a comprehensive collection of answers on linuxtopia sed FAQ  It also highlights that some answers people provided won t work with non-GNU version of sed  eg    sed  0  RE s  to that   file   in  non-GNU version will have to be   sed -e  1s RE to that  t  -e  1  RE s  to that     However  this version won t work with gnu sed     Here s a version that works with both   -e   RE  s  to that   a  -e    N   ba  -e       ex   sed -e   Apple  s  Banana   a  -e    N   ba  -e     filename

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This might work for you  GNU sed    sed -si    include  s   amp   newfile h n amp    a    n ba    file1 file2 file       or if memory is not a problem   sed -si   a    N ba  s  include  amp   newfile h n amp    file1 file2 file

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If anyone came here to replace a character for the first occurrence in all lines  like myself   use this   sed   old s old new 1  file  -bash-4 2  cat file 123a456a789a 12a34a56 a12 -bash-4 2  sed   a s a b 1  file 123b456a789a 12b34a56 b12   By changing 1 to 2 for example  you can replace all the second a s only instead

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Nothing new but perhaps a little more concrete answer  sed -rn  0  foo bar     s   1 p   Example  xwininfo -name unity-launcher produces output like   xwininfo  Window id  0x2200003  unity-launcher     Absolute upper-left X   -2980   Absolute upper-left Y   -198   Relative upper-left X   0   Relative upper-left Y   0   Width  2880   Height  98   Depth  24   Visual  0x21   Visual Class  TrueColor   Border width  0   Class  InputOutput   Colormap  0x20  installed    Bit Gravity State  ForgetGravity   Window Gravity State  NorthWestGravity   Backing Store State  NotUseful   Save Under State  no   Map State  IsViewable   Override Redirect State  no   Corners    -2980 -198  -2980 -198  -2980-1900   -2980-1900   -geometry 2880x98 -2980 -198   Extracting window ID with xwininfo -name unity-launcher sed -rn  0   xwininfo  Window id   0x 0-9a-fA-F       s   1 p  produces   0x2200003

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Using FreeBSD ed and avoid ed s  no match  error in case there is no include statement in a file to be processed    teststr    include  lt stdio h gt   include  lt stdlib h gt   include  lt inttypes h gt       using FreeBSD ed   to avoid ed s  no match  error  see    emphasized text http   codesnippets joyent com posts show 11917  cat  lt  lt - EOF    sed -e  s        -e  s          ed -s  lt  echo   teststr      H     g    include u     u     i      include  newfile h            p    q EOF

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With GNU sed s -z option you could process the whole file as if it was only one line  That way a s          would only replace the first match in the whole file  Remember  s          only replaces the first match in each line  but with the -z option sed treats the whole file as a single line   sed -z  s  include  include  newfile h  n include    In the general case you have to rewrite your sed expression since the pattern space now holds the whole file instead of just one line  Some examples    s text     can be rewritten as s text   n         n  matches everything except the newline character     n   will match all symbols after text until a newline is reached  s  text   can be rewritten as s     n text    s text    can be rewritten as s text  n

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Just add the number of occurrence at the end   sed s  include  include  newfile h  n include 1

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i would do this with an awk script   BEGIN  i 0   i  0   amp  amp    include   print   include   newfile h     i 1   print  0      END      then run it with awk   awk -f awkscript headerfile h  gt  headerfilenew h   might be sloppy  I m new to this

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A possible solution         include   p d       i       include  newfile h       a     n     ba   Explanation    read lines until we find the  include  print these lines then start new cycle insert the new include line enter a loop that just reads lines  by default sed will also print these lines   we won t get back to the first part of the script from here

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i would do this with an awk script   BEGIN  i 0   i  0   amp  amp    include   print   include   newfile h     i 1   print  0      END      then run it with awk   awk -f awkscript headerfile h  gt  headerfilenew h   might be sloppy  I m new to this

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As an alternative suggestion you may want to look at the ed command   man 1 ed  teststr    include  lt stdio h gt   include  lt stdlib h gt   include  lt inttypes h gt       for in-place file editing use  ed -s file  and replace   p  with  w    cf  http   wiki bash-hackers org howto edit-ed cat  lt  lt - EOF    sed -e  s        -e  s          ed -s  lt  echo   teststr      H        include i     include  newfile h           p    q EOF

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You could use awk to do something similar    awk    include   amp  amp   done   print   include   newfile h     done 1    1   file c   Explanation     include   amp  amp   done   Runs the action statement between    when the line matches   include  and we haven t already processed it    print   include   newfile h     done 1     This prints  include  newfile h   we need to escape the quotes  Then we set the done variable to 1  so we don t add more includes   1    This means  print out the line  - an empty action defaults to print  0  which prints out the whole line  A one liner and easier to understand than sed IMO  -

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A possible solution here might be to tell the compiler to include the header without it being mentioned in the source files  IN GCC there are these options      -include file        Process file as if   include  file   appeared as the first line of        the primary source file   However  the first directory searched for        file is the preprocessor s working directory instead of the        directory containing the main source file   If not found there  it        is searched for in the remainder of the   include        search        chain as normal          If multiple -include options are given  the files are included in        the order they appear on the command line      -imacros file        Exactly like -include  except that any output produced by scanning        file is thrown away   Macros it defines remain defined   This        allows you to acquire all the macros from a header without also        processing its declarations          All files specified by -imacros are processed before all files        specified by -include    Microsoft s compiler has the  FI  forced include  option   This feature can be handy for some common header  like platform configuration  The Linux kernel s Makefile uses -include for this

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A sed script that will only replace the first occurrence of  Apple  by  Banana   Example         Input       Output        Apple       Banana      Apple       Apple      Orange      Orange      Apple       Apple   This is the simple script  Editor s note  works with GNU sed only   sed  0  Apple  s Apple Banana    input filename   The first two parameters 0 and  Apple  are the range specifier   The s Apple Banana  is what is executed within that range  So in this case  within the range of the beginning  0  up to the first instance of Apple  replace Apple with Banana   Only the first Apple will be replaced   Background  In traditional sed the range specifier is also  begin here  and  end here   inclusive    However the lowest  begin  is the first line  line 1   and if the  end here  is a regex  then it is only attempted to match against on the next line after  begin   so the earliest possible end is line 2   So since range is inclusive  smallest possible range is  2 lines  and smallest starting range is both lines 1 and 2  i e  if there s an occurrence on line 1  occurrences on line 2 will also be changed  not desired in this case   GNU sed adds its own extension of allowing specifying start as the  pseudo  line 0 so that the end of the range can be line 1  allowing it a range of  only the first line  if the regex  matches the first line   Or a simplified version  an empty RE like    means to re-use the one specified before it  so this is equivalent    sed  0  Apple  s  Banana    input filename   And the curly braces are optional for the s command  so this is also equivalent   sed  0  Apple s  Banana   input filename   All of these work on GNU sed only   You can also install GNU sed on OS X using homebrew brew install gnu-sed

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sed  0  pattern s pattern replacement   filename   this worked for me   example  sed  0   lt Menu gt  s  lt Menu gt   lt Menu gt  lt Menu gt Sub menu lt   Menu gt    try txt  gt  abc txt   Editor s note  both work with GNU sed only

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The following command removes the first occurrence of a string  within a file  It removes the empty line too  It is presented on an xml file  but it would work with any file    Useful if you work with xml files and you want to remove a tag  In this example it removes the first occurrence of the  isTag  tag   Command    sed -e 0    lt isTag gt false lt   isTag gt    s   lt isTag gt false lt   isTag gt       -e  s        -e       d   source txt  gt  output txt   Source file  source txt    lt xml gt       lt testdata gt           lt canUseUpdate gt true lt  canUseUpdate gt           lt isTag gt false lt  isTag gt           lt moduleLocations gt               lt module gt esa jee6 lt  module gt               lt isTag gt false lt  isTag gt           lt  moduleLocations gt           lt node gt               lt isTag gt false lt  isTag gt           lt  node gt       lt  testdata gt   lt  xml gt    Result file  output txt    lt xml gt       lt testdata gt           lt canUseUpdate gt true lt  canUseUpdate gt           lt moduleLocations gt               lt module gt esa jee6 lt  module gt               lt isTag gt false lt  isTag gt           lt  moduleLocations gt           lt node gt               lt isTag gt false lt  isTag gt           lt  node gt       lt  testdata gt   lt  xml gt    ps  it didn t work for me on Solaris SunOS 5 10  quite old   but it works on Linux 2 6  sed version 4 1 5

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I finally got this to work in a Bash script used to insert a unique timestamp in each item in an RSS feed           sed  1      RSSpermalink     s     RSSpermalink       nowms                  production-feed2 xml tmp2  gt  production-feed2 xml tmp  counter   It changes the first occurrence only      nowms  is the time in milliseconds set by a Perl script   counter is a counter used for loop control within the script    allows the command to be continued on the next line   The file is read in and stdout is redirected to a work file   The way I understand it  1      RSSpermalink      tells sed when to stop by setting a range limitation  and then s     RSSpermalink       nowms   is the familiar sed command to replace the first string with the second    In my case I put the command in double quotation marks becauase I am using it in a Bash script with variables

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sed script to change  foo  to  bar  only on the first occurrence  1 x s   first  x    1  foo  x  first s    x s foo bar      ---end of script---   or  if you prefer  Editor s note  works with GNU sed only   sed  0  foo s  bar   file    Source

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sed -e  s pattern REPLACEMENT 1   lt INPUTFILE

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The use case can perhaps be that your occurences are spread throughout your file  but you know your only concern is in the first 10  20 or 100 lines   Then simply adressing those lines fixes the issue - even if the wording of the OP regards first only   sed  1 10s  include  include  newfile h  n include

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An overview of the many helpful existing answers  complemented with explanations  The examples here use a simplified use case  replace the word  foo  with  bar  in the first matching line only  Due to use of ANSI C-quoted strings          to provide the sample input lines  bash  ksh  or zsh is assumed as the shell    GNU sed only  Ben Hoffstein s anwswer shows us that GNU  provides an extension to the POSIX specification for sed that allows the following 2-address form  0  re   re represents an arbitrary regular expression here   0  re  allows the regex to match on the very first line also  In other words  such an address will create a range from the 1st line up to and including the line that matches re - whether re occurs on the 1st line or on any subsequent line   Contrast this with the POSIX-compliant form 1  re   which creates a range that matches from the 1st line up to and including the line that matches re on subsequent lines  in other words  this will not detect the first occurrence of an re match if it happens to occur on the 1st line and also prevents the use of shorthand    for reuse of the most recently used regex  see next point  1  If you combine a 0  re  address with an s           substitution  call that uses the same regular expression  your command will effectively only perform the substitution on the first line that matches re  sed provides a convenient shortcut for reusing the most recently applied regular expression  an empty delimiter pair        sed  0  foo  s  bar    lt  lt  lt   1st foo nUnrelated n2nd foo n3rd foo   1st bar           only 1st match of  foo  replaced Unrelated 2nd foo 3rd foo   A POSIX-features-only sed such as BSD  macOS  sed  will also work with GNU sed   Since 0  re  cannot be used and the form 1  re  will not detect re if it happens to occur on the very first line  see above   special handling for the 1st line is required  MikhailVS s answer mentions the technique  put into a concrete example here    sed -e  1 s foo bar   t  -e  1    s  bar    lt  lt  lt   1st foo nUnrelated n2nd foo n3rd foo  1st bar           only 1st match of  foo  replaced Unrelated 2nd foo 3rd foo  Note   The empty regex    shortcut is employed twice here  once for the endpoint of the range  and once in the s call  in both cases  regex foo is implicitly reused  allowing us not to have to duplicate it  which makes both for shorter and more maintainable code   POSIX sed needs actual newlines after certain functions  such as after the name of a label or even its omission  as is the case with t here  strategically splitting the script into multiple -e options is an alternative to using an actual newlines  end each -e script chunk where a newline would normally need to go    1 s foo bar  replaces foo on the 1st line only  if found there  If so  t branches to the end of the script  skips remaining commands on the line    The t function branches to a label only if the most recent s call performed an actual substitution  in the absence of a label  as is the case here  the end of the script is branched to   When that happens  range address 1     which normally finds the first occurrence starting from line 2  will not match  and the range will not be processed  because the address is evaluated when the current line is already 2  Conversely  if there s no match on the 1st line  1    will be entered  and will find the true first match  The net effect is the same as with GNU sed s 0  re   only the first occurrence is replaced  whether it occurs on the 1st line or any other   NON-range approaches potong s answer demonstrates loop techniques that bypass the need for a range  since he uses GNU sed syntax  here are the POSIX-compliant equivalents  Loop technique 1  On first match  perform the substitution  then enter a loop that simply prints the remaining lines as-is    sed -e   foo   s  bar     -e   a  -e     n ba  -e        lt  lt  lt   1st foo nUnrelated n2nd foo n3rd foo  1st bar Unrelated 2nd foo 3rd foo  Loop technique 2  for smallish files only  read the entire input into memory  then perform a single substitution on it    sed -e   a  -e     N ba  -e     s foo bar    lt  lt  lt   1st foo nUnrelated n2nd foo n3rd foo  1st bar Unrelated 2nd foo 3rd foo   1 1 61803 provides examples of what happens with 1  re   with and without a subsequent s     sed  1  foo  s foo bar    lt  lt  lt   1foo n2foo  yields   1bar n2bar   i e   both lines were updated  because line number 1 matches the 1st line  and regex  foo  - the end of the range - is then only looked for starting on the next line  Therefore  both lines are selected in this case  and the s foo bar  substitution is performed on both of them  sed  1  foo  s  bar    lt  lt  lt   1foo n2foo n3foo  fails  with sed  first RE may not be empty  BSD macOS  and sed  -e expression  1  char 0  no previous regular expression  GNU   because  at the time the 1st line is being processed  due to line number 1 starting the range   no regex has been applied yet  so    doesn t refer to anything  With the exception of GNU sed s special 0  re  syntax  any range that starts with a line number effectively precludes use of

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POSIXly  also valid in sed   Only one regex used  need memory only for one line  as usual    sed      include      b    h s   1  newfile h   G   1 n b1    Explained   sed       include      b            Only one regex used  On lines not matching                               the text    include    yet                                  branch to end  cause the default print  Re-start                                On first line matching previous regex      h                         hold the line      s   1  newfile h          append    newfile h   to the   include  matched      G                         append a newline                                end of replacement   1                            Once   one   replacement got done  the first match  n                             Loop continually reading a line each time b1                            and printing it by default                                end of sed script

[command-line] How to use sed to replace only the first occurrence in a file?

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