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I have an external program that produces an output file (largish, 20K lines possible).
I need to insert a new line between the existing line 1 and line 2. I've been looking at awk and sed - I use one liners in each fairly regularly - but I haven't been able to come up with the right switches to do this.
awk 'NR==1{print; print "new line"} NR!=1'
For your specific case, this should be simpler:
sed '1 { P ; x }' your-file
Explanation: at line 1, do the following
Then, the line (empty now) is printed again as part of the cycle.
If you want to add a new line instead of a new line character (what I understood initially) then just use sed's command a\ (append):
sed '1 a\
appended line' your-file
or even
sed '1 aappended line' your-file
It appends "appended line" after line 1.
'1 aapended line' example.
I guess the sed approach would be:
sed '2 i whatever_line_of_text_you_wanted_to_INSERT' filename.txt
This will get the text into the second line of the file and then the the actual second line with in the file will become the third.
Note that, using append mode, if it had to be, it had to use the first line, since the append will happen after the line number noted.
sed '1 a whatever_line_of_text_you_wanted_to_INSERT' filename.txt
None of the answers above mention how to save the changes to the original file, which is I think what the OP was asking for.
It's certainly what I needed when I cam to the page.
So assuming your file is called output.txt
sed -i '1 a This is the second line' output.txt
My particular use case is to automatically add an xsl stylesheet declaration to a junit xml file.
sed -i '1 a <?xml-stylesheet type="text/xsl" href="junit-html.xsl"?>' junit.xml
sed ':a;N;$!ba;s/\n/\n\n\n/' yourBigFile
This might work for you:
sed 1G file
If you want to insert something after the newline:
sed '1{G;s/$/something/}' file
Or if you sed handles \n:
sed '1s/$/\nsomething/' file
Of course a is even easier:
sed '1a something' file
I usually use ed for this:
(echo 1a; echo 'Line to insert'; echo .; echo w) | ed - filename
Similar to a sed solution, but without the clutter of escaped newlines.
echo's, especially under bash: ed - filename <<< $'1a\nLine to insert\n.\nw'.
Jan 28, 2012 at 16:56
dash, which on many systems is /bin/sh.
echo's”. Sparing all echo's is indeed bash only feature, but reducing the echo count from 4 to 1 works in dash and ksh too: echo '1a\nLine to insert\n.\nw' | ed - filename.
Jan 28, 2012 at 17:37
printf %s\\n, which puts a newline after every arg you give it and doesn't screw up on special characters embedded in the line you want to insert. Also, why use ed when ex is available?
Python Solution
python -c "import sys; lines = sys.stdin.readlines(); lines.insert(1,'New Line\n'); print ''.join(lines).strip()" < input.txt
Using sed and (Bash-specific) ANSI escape codes:
# note: \ --> \\
printf '%s\n' 1 2 3 4 5 | sed -e $'1 { s/\\(.*\\)/\\1\\\ninserted line/; }'
i would use python for this
import fileinput
for linenum,line in enumerate(fileinput,FileInput("file",inplace=1)):
if linenum ==1:
print ""
print line.rstrip()
else:
print line.rstrip()`
I just like using an explicit counter:
awk '(c==1) {print "new line"} (c!=1) {print $0} {c++}' file
Simplest method uses printf and ex:
printf '%s\n' 1a 'my line to insert' . x | ex file
1a means "append after first line"; the . ends the appending; x means save and exit.
