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Editing Every 10th Line of a File

Hi,

I am trying to replace the first word of every 10th line in a file. What would be the most efficient language to do this.

Thanks.

Quote:

Originally Posted by linux26f (Post 4565041)

Hi,
I am trying to replace the first word of every 10th line in a file. What would be the most efficient language to do this.
Thanks.

No idea, without some context. How big is the file? What kind of replacement are you talking about? (regex type string, or static?) Variable file names each time, or the same?

If you mean just a small-ish text file, replacing something like "string1" with "string2", bash would work fine. If you're talking about a 20GB file, and replacing strings like "Item-A13802-CL" with "ItemBCL13802", that's more of a job for Perl, or another more heavy-duty language.

Hi.

GNU sed has a feature that allows firstline-step addresses, like so:

Code:

#!/usr/bin/env bash



# @(#) s1        Demonstrate first~step address selection for GNU sed.



# Utility functions: print-as-echo, print-line-with-visual-space, debug.

# export PATH="/usr/local/bin:/usr/bin:/bin"

pe() { for _i;do printf "%s" "$_i";done; printf "\n"; }

pl() { pe;pe "-----" ;pe "$*"; }

db() { ( printf " db, ";for _i;do printf "%s" "$_i";done;printf "\n" ) >&2 ; }

db() { : ; }

C=$HOME/bin/context && [ -f $C ] && $C sed



FILE=${1-data1}



pl " Input data file $FILE:"

cat $FILE



pl " Results:"

sed -r '2~3s/^\w+/changed to this string/' $FILE



exit 0

producing:

Code:

% ./s1



Environment: LC_ALL = C, LANG = C

(Versions displayed with local utility "version")

OS, ker|rel, machine: Linux, 2.6.26-2-amd64, x86_64

Distribution        : Debian GNU/Linux 5.0.8 (lenny) 

GNU bash 3.2.39

GNU sed version 4.1.5



-----

 Input data file data1:

Bruckner kinetic cordon cryptography bantam calendrical

venture antagonistic. Drool adsalsey barbarism

horseshoe pappy acrylate. Dayton Friedrich inn maxima

capita sract vicar accordant. Sinai forgettable

ointment Hippocrates swampy hotelman upturn Kobayashi.

Kingsbury chorus gracte David Marty slavish!

Ophthalmology whixalvy int look fraught. Klelengy

ajectalk Bausch ordnance sturgeon hike Renault Kruse

prep gases potassium. Gallon carefree libation Ronnie

plasmon crust barbudo irchotche.



-----

 Results:

Bruckner kinetic cordon cryptography bantam calendrical

changed to this string antagonistic. Drool adsalsey barbarism

horseshoe pappy acrylate. Dayton Friedrich inn maxima

capita sract vicar accordant. Sinai forgettable

changed to this string Hippocrates swampy hotelman upturn Kobayashi.

Kingsbury chorus gracte David Marty slavish!

Ophthalmology whixalvy int look fraught. Klelengy

changed to this string Bausch ordnance sturgeon hike Renault Kruse

prep gases potassium. Gallon carefree libation Ronnie

plasmon crust barbudo irchotche.

Note that the separator is a tilde, not a dash. See GNU man sed for details ... cheers, makyo

( edit 1: forgot option "-r" )

1) Make sure you think of a string that is NOT present in the file. For example, "WOOTWOOT".

2) Add line number and "WOOTWOOT" before every line:

Code:

% nl -s " WOOTWOOT " file.txt > tempfile1.txt

Check tempfile1.txt and you will understand:

Code:

% less tempfile1.txt

3) Now the line number of every TENTH line MUST end in "0" (zero), therefore you can safely replace whatever you want in every line that contains "some number, ZERO, space, WOOTWOOT and space". That's a perfect job for sed:

Code:

% sed 's/[0-9]*0 WOOTWOOT /s/find this string/replace with this string/' tempfile1.txt > tempfile2.txt

4) Now let's clean the line numbers and WOOTWOOTs of the resulting file:

Code:

% sed 's/^.*WOOTWOOT //' tempfile2.txt > tempfile1.txt

5) Now check tempfile1.txt, it must be just the way you want it. If you're happy with the result, use it:

Code:

% mv tempfile1.txt file.txt

Code:

perl -i.bak -pe '$_=~s/\s*(\w+)/Word Replacement/ if $.=~/0$/' file

file updated in place and original saved as file.bak

(edit)
added \s just in case there are some space chars before the first word