how to remove the first line from a flat file ?


 
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# 8  
Old 03-17-2005
Quote:
Originally Posted by zazzybob
Not always - it depends on which version of sed you're using.... GNU sed supports the -i option to edit files in place (a backup extension can also be supplied much like perls -i option).

Observe...
Code:
$ cat > flatfile
1st line
2nd line
3rd line
^D
$ sed -i '1d' flatfile
$ more flatfile
2nd line
3rd line

Cheers
ZB
ZB.. it worked for me using cygwin.
# 9  
Old 03-17-2005
Quote:
Originally Posted by tanku
ZB.. it worked for me using cygwin.
Yes it will work with Cygwin as Cygwin includes GNU sed...
Code:
someone@cygwin $ sed --version
GNU sed version 4.0.7

Cheers
ZB
# 10  
Old 03-17-2005
out of curiosity i wanted to find out how long it would take to complete the task on my computer (cygwin on windows)... i created a huge file

the winner is................

Code:
$ wc -l bigfatfile
15711759 bigfatfile

$ time sed -i.bk '1d' bigfatfile

real    3m1.870s
user    2m2.406s
sys     0m23.906s

$ time perl -pi.bk -e '$_ = "" if ($. == 1);' bigfatfile

real    1m46.065s
user    0m0.015s
sys     0m0.016s

$ time printf ":1d\n:wq\n" | ex bigfatfile

real    6m53.646s
user    1m52.295s
sys     0m19.374s

perl!!!!!!!!!!!!!
# 11  
Old 03-17-2005
Quote:
Originally Posted by tanku
out of curiosity i wanted to find out how long it would take to complete the task on my computer (cygwin on windows)... i created a huge file

the winner is................

Code:
$ wc -l bigfatfile
15711759 bigfatfile

$ time sed -i.bk '1d' bigfatfile

real    3m1.870s
user    2m2.406s
sys     0m23.906s

$ time perl -pi.bk -e '$_ = "" if ($. == 1);' bigfatfile

real    1m46.065s
user    0m0.015s
sys     0m0.016s

$ time printf ":1d\n:wq\n" | ex bigfatfile

real    6m53.646s
user    1m52.295s
sys     0m19.374s

perl!!!!!!!!!!!!!
Yeah, same result here, but for additional reasons, on Solaris 9
Filesize 1.7GB, 20,442,408 lines

sed doesn't support -i
file is too large for ex

Cpu usage for perl on idle V240:
40.89u 15.75s 0:57.99 97.6%
# 12  
Old 03-30-2005
A Little extra

I found this feed and it answers half of my problem....
once I remove the first line from a flat file.How can I put that removed line into a variable or anouther flate file or both???

Thanx for any help.
# 13  
Old 03-30-2005
you could just do:

head -1 filename

before deleting the line.
# 14  
Old 03-30-2005
Or, using the perl solution

Code:
FIRSTLINE=`perl -pi.bk -e 'print( STDOUT $_ ) and $_= "" if ($. == 1);' bigfatfile`

Then, you'll get the value of the first line stored in the FIRSTLINE variable, and the line will be deleted from "bigfatfile". Alternatively, just redirect to another file...
Code:
perl -pi.bk -e 'print( STDOUT $_ ) and $_= "" if ($. == 1);' bigfatfile > first_line

Cheers
ZB
 
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