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Numbering Lines


2006/11/15

Now and then you want to number the lines of a file. You can roll your own script to do that:

#!/bin/bash
x=1;
while read line
do
echo -n "$x: "
echo $line
x=$((x+1))
done



If you run that on itself ("thescript < thescript"), you get:

1: #!/bin/bash
2: x=1;
3: while read line
4: do
5: echo -n "$x: "
6: echo $line
7: x=$((x+1))
8: done

You get something very similar to that with "nl thescript":


$ nl thescript
1 #!/bin/bash
2 x=1;
3 while read line
4 do
5 echo -n "$x: "
6 echo $line
7 x=$((x+1))
8 done
$

On most systems, "cat -n" works just like "nl", but "nl" has more tricks up its sleeves. If we add some blank lines to our file, one difference becomes obvious:


$ nl thescript
1 #!/bin/bash
2 x=1;
3 while read line
4 do

5 echo -n "$x: "
6 echo $line
7 x=$((x+1))

8 done
$ cat -n thescript

1 #!/bin/bash
2 x=1;
3 while read line
4 do
5
6 echo -n "$x: "
7 echo $line
8 x=$((x+1))
9
10 done

"nl" has flags to turn on numbering for blank lines and to use a different increment. It can restart numbering at each new page (or not), or number only those lines containing certain text ('nl -b pecho thescript'). Check the man page; nl is a powerful little tool.

Several other tools have switches to add line numbering: pr, a2ps and enscript are a few I can think of immediately, but there are surely many more. Word processors have this too; in Microsoft Word it's under Page Layout. Even crappy old MSDOS apparently can do that.

Let's not forget 'awk':

awk '{printf "%3d: %s\n", NR, $0}' thescript

Very often I just want to know about line numbers while in "vi". There are two ways to do that: ":.=" (colen period equal) will tell you the number of the current line, and ":set number" will turn on numbering ahead of each line (the numbers aren't written out when you save the file). Turn numbering off with ":set nonumber". Of course emacs has similar features.

By the way: I never use emacs voluntarily, so when I am forced to, I can never remember how to get out of the darn thing. People who never use vi probably have a similar problem. For vi, hit ESCAPE, then ":q!(ENTER)" to get out without writing. If you DO want to write, use ":wq(ENTER)". To exit emacs, use CTRL-X CTRL-C. If you are stuck in some Emacs command (again: I HATE Emacs!), try Ctrl-G a couple of times. For "ed", just type "q!(ENTER)", or "wq(ENTER)" if you want to write. If those don't work, just type enter and then ".(ENTER)"



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2 comments



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© Anthony Lawrence







Sun Mar 9 23:57:14 2008: 3825   anonymous


there's one thing that's different about line numbering in microsoft word:
it doesn't number based on newline, CR, LF, or the like.
it numbers based on the margins of the page.
i am trying to find a way to replicate this in unix.
any ideas?



Mon Mar 10 11:10:22 2008: 3826   TonyLawrence

gravatar
You just make the physical format match the margins you want, using "fmt" or whatever.





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