Insert a line at specific line number with sed or awk

Question

I have a script file which I need to modify with another script to insert a text at the 8th line.

String to insert: Project_Name=sowstest, into a file c

Answer 1

An ed answer

ed file << END
8i
Project_Name=sowstest
.
w
q
END

. on its own line ends input mode; w writes; q quits. GNU ed has a wq command to save and quit, but old ed's don't.

Further reading: https://gnu.org/software/ed/manual/ed_manual.html

Answer 2

Perl solutions:

quick and dirty:

perl -lpe 'print "Project_Name=sowstest" if $. == 8' file

• -l strips newlines and adds them back in, eliminating the need for "\n"
  
• -p loops over the input file, printing every line
  
• -e executes the code in single quotes
  

$. is the line number

equivalent to @glenn's awk solution, using named arguments:

perl -slpe 'print $s if $. == $n' -- -n=8 -s="Project_Name=sowstest" file

• -s enables a rudimentary argument parser
  
• -- prevents -n and -s from being parsed by the standard perl argument parser
  

positional command arguments:

perl -lpe 'BEGIN{$n=shift; $s=shift}; print $s if $. == $n' 8 "Project_Name=sowstest" file

environment variables:

setenv n 8 ; setenv s "Project_Name=sowstest"
echo $n ; echo $s
perl -slpe 'print $ENV{s} if $. == $ENV{n}' file

ENV is the hash which contains all environment variables

Getopt to parse arguments into hash %o:

perl -MGetopt::Std -lpe 'BEGIN{getopt("ns",\%o)}; print $o{s} if $. == $o{n}' -- -n 8 -s "Project_Name=sowstest" file

Getopt::Long and longer option names

perl -MGetopt::Long -lpe 'BEGIN{GetOptions(\%o,"line=i","string=s")}; print $o{string} if $. == $o{line}' -- --line 8 --string "Project_Name=sowstest" file

Getopt is the recommended standard-library solution.
This may be overkill for one-line perl scripts, but it can be done

Answer 3

For those who are on SunOS which is non-GNU, the following code will help:

sed '1i\^J
line to add' test.dat > tmp.dat

• ^J is inserted with ^V+^J
• Add the newline after '1i.
• \ MUST be the last character of the line.
• The second part of the command must be in a second line.

Answer 4

sed -i "" -e $'4 a\\n''Project_Name=sowstest' start

• This line works fine in macOS

Answer 5

sed -e '8iProject_Name=sowstest' -i start using GNU sed

Sample run:

[root@node23 ~]# for ((i=1; i<=10; i++)); do echo "Line #$i"; done > a_file
[root@node23 ~]# cat a_file
Line #1
Line #2
Line #3
Line #4
Line #5
Line #6
Line #7
Line #8
Line #9
Line #10
[root@node23 ~]# sed -e '3ixxx inserted line xxx' -i a_file 
[root@node23 ~]# cat -An a_file 
     1  Line #1$
     2  Line #2$
     3  xxx inserted line xxx$
     4  Line #3$
     5  Line #4$
     6  Line #5$
     7  Line #6$
     8  Line #7$
     9  Line #8$
    10  Line #9$
    11  Line #10$
[root@node23 ~]# 
[root@node23 ~]# sed -e '5ixxx (inserted) "line" xxx' -i a_file
[root@node23 ~]# cat -n a_file 
     1  Line #1
     2  Line #2
     3  xxx inserted line xxx
     4  Line #3
     5  xxx (inserted) "line" xxx
     6  Line #4
     7  Line #5
     8  Line #6
     9  Line #7
    10  Line #8
    11  Line #9
    12  Line #10
[root@node23 ~]# 

Answer 6

POSIX sed (and for example OS X's sed, the sed below) require i to be followed by a backslash and a newline. Also at least OS X's sed does not include a newline after the inserted text:

$ seq 3|gsed '2i1.5'
1
1.5
2
3
$ seq 3|sed '2i1.5'
sed: 1: "2i1.5": command i expects \ followed by text
$ seq 3|sed $'2i\\\n1.5'
1
1.52
3
$ seq 3|sed $'2i\\\n1.5\n'
1
1.5
2
3

To replace a line, you can use the c (change) or s (substitute) commands with a numeric address:

$ seq 3|sed $'2c\\\n1.5\n'
1
1.5
3
$ seq 3|gsed '2c1.5'
1
1.5
3
$ seq 3|sed '2s/.*/1.5/'
1
1.5
3

Alternatives using awk:

$ seq 3|awk 'NR==2{print 1.5}1'
1
1.5
2
3
$ seq 3|awk '{print NR==2?1.5:$0}'
1
1.5
3

awk interprets backslashes in variables passed with -v but not in variables passed using ENVIRON:

$ seq 3|awk -v v='a\ba' '{print NR==2?v:$0}'
1
a
3
$ seq 3|v='a\ba' awk '{print NR==2?ENVIRON["v"]:$0}'
1
a\ba
3

Both ENVIRON and -v are defined by POSIX.