How to use a command inside sed

ZAMO · 02-27-2009, 01:07 AM

Hi all ,

Am trying to print the last n lines of a file using sed, but am unable to do a echo within sed. can someone correct me?

Code:

sed -n '1,40' linetest

is working

if n=40 (am got this from some other output)

I try to the following and failed.

Code:

sed -n '1,"/`echo $num`/"p' linetest

I want to print the first n lines only .I want a substitute for

Code:

head -`echo $num`  linetest

using sed.

Thanks

sycamorex · 02-27-2009, 01:42 AM

To print the last 5 lines of a file you would use:

Code:

sed -e :a -e '$q;N;6,$D;ba' file

To print the first 5 lines:

sed -n '1,5p' file

I don't know how to pass values to sed commands, though.

ZAMO · 02-27-2009, 04:19 AM

I got that with this option.

Code:

sed -n "1,`echo $num`p" linetest

Thanks sycamorex

H_TeXMeX_H · 02-27-2009, 04:37 AM

I usually do:

Code:

sed -n '1,'"$(echo $num)"'p' linetest