The Line Number Command ‘=’ :: SED

The Spec on ‘=’

sed spec excerpt on = command

[1addr]=
    Write the following to standard output:

    "%d\n", <current line number>

Open the spec and search for “[1addr]=”.

Yep, it prints the current line number followed by a newline.

It means the line number and the line content will not be on the same line:

$ sed = < ./poem1.txt
1
Roses are #ff0000
2
Violets are #0000ff
3
If you can read this
4
You are a n3rd too!

Some Ideas on Using ‘=’

With -n, we suppress outputting the pattern space so that only the line numbers (each on its own line, according to the spec) are printed:

$ sed -n = < ./poem1.txt
1
2
3
4

No easy way to print the line numbers on the same output lines with one single sed, but two sed invocations will do:

$ sed = < ./poem1.txt  | sed 'N; s/\n/ /'
1 Roses are #ff0000
2 Violets are #0000ff
3 If you can read this
4 You are a n3rd too!

Maybe add something between the line number and the actual line contents:

$ sed = < ./poem1.txt  | sed 'N; s/\n/ → /'
1 → Roses are #ff0000
2 → Violets are #0000ff
3 → If you can read this
4 → You are a n3rd too!

$ sed = < ./poem1.txt  | sed 'N; s/\n/. /'
1. Roses are #ff0000
2. Violets are #0000ff
3. If you can read this
4. You are a n3rd too!

Since = command can take an address, we can use it to print the number of the last line to mimic to wc -l:

$ sed -n '$=' < ./poem1.txt
4

$ wc -l < ./poem1.txt
4