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sed delete option

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# 1  
Old 05-01-2011
sed delete option
I have tried doing this to delete some lines:
Code:
sed '1,10d' file

Now I want to specify a variable as a line number for example:

lastline=wc -l file
linestart=$lastline - 20

sed '$linestart,$lastlined' file

but this will give error:
Code:
sed: -e expression #1, char 3: extra characters after command

Is there anyway to place a variable as the line number?
Last edited by Yogesh Sawant; 05-01-2011 at 05:09 AM.. Reason: added code tags
# 2  
Old 05-01-2011
Code:
tail -r infile | tail +21 | tail -r

Code:
tail -r infile | tail -n +21 | tail -r

Code:
$ cat tst
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
$ tail -r tst | tail +21 | tail -r
1
2
3
4
5
6
7
8
9
10

---------- Post updated at 09:32 AM ---------- Previous update was at 09:28 AM ----------

Code:
$ lastline=$(wc -l yourfile)
$ awk -v c="$lastline" 'NR<=c-20' yourfile
1
2
3
4
5
6
7
8
9
10

# 3  
Old 05-01-2011
Use double quotes
Code:
sed "$start,$end d" file

Or, if you have metacharacters in there, use single quotes and turn them on and off to get the $start and $end in:
Code:
 sed ''$start','$end' d' file

The same way you can sneak in variables into regex's.
This User Gave Thanks to mirni For This Post:
zorrox
# 4  
Old 05-01-2011
Code:
$ lastline=$(( $(wc -l <tst)-20 ))
$ sed '1,'$lastline'!d' tst
1
2
3
4
5
6
7
8
9
10

This User Gave Thanks to ctsgnb For This Post:
zorrox
# 5  
Old 05-01-2011
Thanks mirni. Your code works very well. You the best.
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