UNIX for Dummies Questions & Answers

Dear users,

I need to count the number of lines in a simple text file and print the number on the first line of that same file.

I know I can count the lines using

wc -l file.txt

this gives for example

100 file.txt

I need the number 100 to be printed at the very top of file.txt i.e above the existing text (I dont want the file.txt printed).

Any help much appreciated,

If your sed has -i feature,

Code:

$ cat > testfile
testing line1
testing line2
$ 
$ numberoflines=`wc -l < testfile`
$ sed -i "1s/^/$numberoflines/" testfile 
$ cat testfile 
2testing line1
testing line2

Code:

$ awk '{a[NR]=$0}END {print NR; for (i=1;i<=NR;i++) print a[i]}' testfile
2
testing line1
testing line2