Insert line after first match using sed

Question

For some reason I can t seem to find a straightforward answer to this and I m on a bit of a time crunch at the moment   How would I go about inserting a choice line of text after the first line matching a specific string using the sed command   I have      CLIENTSCRIPT  foo  CLIENTFILE  bar    And I want insert a line after the CLIENTSCRIPT  line resulting in      CLIENTSCRIPT  foo  CLIENTSCRIPT2  hello  CLIENTFILE  bar

User · Answer

I had to do this recently as well for both Mac and Linux OS's and after browsing through many posts and trying many things out, in my particular opinion I never got to where I wanted to which is: a simple enough to understand solution using well known and standard commands with simple patterns, one liner, portable, expandable to add in more constraints. Then I tried to looked at it with a different perspective, that's when I realized i could do without the "one liner" option if a "2-liner" met the rest of my criteria. At the end I came up with this solution I like that works in both Ubuntu and Mac which i wanted to share with everyone:

insertLine=$(( $(grep -n "foo" sample.txt | cut -f1 -d: | head -1) + 1 ))
sed -i -e "$insertLine"' i\'$'\n''bar'$'\n' sample.txt

In first command, grep looks for line numbers containing "foo", cut/head selects 1st occurrence, and the arithmetic op increments that first occurrence line number by 1 since I want to insert after the occurrence. In second command, it's an in-place file edit, "i" for inserting: an ansi-c quoting new line, "bar", then another new line. The result is adding a new line containing "bar" after the "foo" line. Each of these 2 commands can be expanded to more complex operations and matching.

User · Answer

A POSIX compliant one using the s command   sed   CLIENTSCRIPT  foo  s     amp   CLIENTSCRIPT2  hello    file

User · Answer

Sed command that works on MacOS  at least  OS 10  and Unix alike  ie  doesn t require gnu sed like Gilles   currently accepted  one does    sed -e   CLIENTSCRIPT  foo  a     n  CLIENTSCRIPT2  hello   file   This works in bash and maybe other shells too that know the    n  evaluation quote style  Everything can be on one line and work in   older POSIX sed commands  If there might be multiple lines matching the CLIENTSCRIPT  foo   or your equivalent  and you wish to only add the extra line the first time  you can rework it as follows    sed -e      CLIENTSCRIPT  foo  b ins  -e b -e   ins  -e  a     n  CLIENTSCRIPT2  hello   -e    done  -e  n b done  file    this creates a loop after the line insertion code that just cycles through the rest of the file  never getting back to the first sed command again    You might notice I added a       to the matching pattern in case that line shows up in a comment  say  or is indented  Its not 100  perfect but covers some other situations likely to be common  Adjust as required     These two solutions also get round the problem  for the generic solution to adding a line  that if your new inserted line contains unescaped backslashes or ampersands they will be interpreted by sed and likely not come out the same  just like the  n is - eg   0 would be the first line matched  Especially handy if you re adding a line that comes from a variable where you d otherwise have to escape everything first using   var    before  or another sed statement etc   This solution is a little less messy in scripts  that quoting and  n is not easy to read though   when you don t want to put the replacement text for the a command at the start of a line if say  in a function with indented lines  I ve taken advantage that    n  is evaluated to a newline by the shell  its not in regular   n  single-quoted values   Its getting long enough though that I think perl even awk might win due to being more readable

User · Answer

Note the standard sed syntax  as in POSIX  so supported by all conforming sed implementations around  GNU  OS X  BSD  Solaris        sed   CLIENTSCRIPT  a  CLIENTSCRIPT2  hello   file   Or on one line   sed -e   CLIENTSCRIPT  a   -e  CLIENTSCRIPT2  hello   file    -expressions  and the contents of -files  are joined with newlines to make up the sed script sed interprets    The -i option for in-place editing is also a GNU extension  some other implementations  like FreeBSD s  support -i    for that   Alternatively  for portability  you can use perl instead   perl -pi -e        qq CLIENTSCRIPT2  hello  n  if  CLIENTSCRIPT    file   Or you could use ed or ex   printf   s n   CLIENTSCRIPT  a  CLIENTSCRIPT2  hello     w q   ex -s file

User · Answer

Maybe a bit late to post an answer for this  but I found some of the above solutions a bit cumbersome    I tried simple string replacement in sed and it worked   sed  s CLIENTSCRIPT  foo   amp  nCLIENTSCRIPT2  hello    file    amp  sign reflects the matched string  and then you add  n and the new line   As mentioned  if you want to do it in-place   sed -i  s CLIENTSCRIPT  foo   amp  nCLIENTSCRIPT2  hello    file   Another thing  You can match using an expression   sed -i  s CLIENTSCRIPT     amp  nCLIENTSCRIPT2  hello    file   Hope this helps someone

User · Answer

Try doing this using GNU sed   sed   CLIENTSCRIPT  foo  a CLIENTSCRIPT2  hello   file   if you want to substitute in-place  use  sed -i   CLIENTSCRIPT  foo  a CLIENTSCRIPT2  hello   file   Output  CLIENTSCRIPT  foo  CLIENTSCRIPT2  hello  CLIENTFILE  bar    Doc   see sed doc and search  a  append

User · Answer

I had a similar task  and was not able to get the above perl solution to work   Here is my solution   perl -i -pe  BEGIN undef      s    mysqld     mysqld  n ncollation-server   utf8 unicode ci n sgm   etc mysql my cnf   Explanation   Uses a regular expression to search for a line in my  etc mysql my cnf file that contained only  mysqld  and replaced it with   mysqld   collation-server   utf8 unicode ci  effectively adding the collation-server   utf8 unicode ci line after the line containing  mysqld

User · Answer

The awk variant     awk  1  CLIENTSCRIPT   print  CLIENTSCRIPT2   hello      file

[shell] Insert line after first match using sed

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