Diff for "BashFAQ/019"

Differences between revisions 1 and 135 (spanning 134 versions)

All greetings! I know you and Jackie will be there, because like the rest of us, motorsport is a passion to you both beer I tell my friends about it! They like sites like that: http://mechanicalid.p8.hu/recipee3d.html recipe look, http://rubyig.p8.hu/recipee12.html cocktail, so hold.

-  ⇤ ← Revision 1 as of 2007-05-02 23:05:11 → 
  Size: 1833
  Editor: redondos
  Comment:
+   ← Revision 135 as of 2009-01-10 17:24:29 → ⇥
  Size: 287
  Editor: chowderly-month
  Comment: -9
-Deletions are marked like this.
+Additions are marked like this.
 Line 1:
-[[Anchor(faq19)]]
== How can I split a file into line ranges, e.g. lines 1-10, 11-20, 21-30? ==
Some Unix systems provide the {{{split}}} utility for this purpose:

{{{
    split --lines 10 --numeric-suffixes input.txt output-
}}}

For more flexibility you can use {{{sed}}}.  The {{{sed}}} command can print e.g. the line number range 1-10:
{{{
    sed -n '1,10p'
}}}

This stops {{{sed}}} from printing each line ({{{-n}}}). Instead it only processes the lines in the range 1-10 ("1,10"), and prints them ("p"). {{{sed}}} still reads the input until the end, although we are only interested in lines 1 though 10. We can speed this up by making {{{sed}}} terminate immediately after printing line 10:

{{{
    sed -n -e '1,10p' -e '10q'
}}}

Now the command will quit after reading line 10 ("10q"). The {{{-e}}} arguments indicate a script (instead of a file name). The same can be written a little shorter:

{{{
    sed -n '1,10p;10q'
}}}

We can now use this to print an arbitrary range of a file (specified by line number):

{{{
file=/etc/passwd
range=10
firstline=1
maxlines=$(wc -l < "$file") # count number of lines
while (($firstline < $maxlines))
do
    ((lastline=$firstline+$range+1))
    sed -n -e "$firstline,${lastline}p" -e "${lastline}q" "$file"
    ((firstline=$firstline+$range+1))
done
}}}

This example uses ["BASH"] and KornShell ArithmeticExpressions, which older [wiki:Self:BourneShell Bourne shells] do not have. In that case the following example should be used instead:

{{{
file=/etc/passwd
range=10
firstline=1
maxlines=`wc -l < "$file"` # count line numbers
while [ $firstline -le $maxlines ]
do
    lastline=`expr $firstline + $range + 1`
    sed -n -e "$firstline,${lastline}p" -e "${lastline}q" "$file"
    firstline=`expr $lastline + 1`
done
}}}
+All greetings! I know you and Jackie will be there, because like the rest of us, motorsport is a passion to you both beer I tell my friends about it! They like sites like that: http://mechanicalid.p8.hu/recipee3d.html recipe look, http://rubyig.p8.hu/recipee12.html cocktail,  so hold.