Diff for "BashFAQ/019"

Differences between revisions 158 and 162 (spanning 4 versions)

How can I split a file into line ranges, e.g. lines 1-10, 11-20, 21-30?

POSIX specifies the split utility, which can be used for this purpose:

   1 split -l 10 input.txt

For more flexibility you can use sed. The sed command can print e.g. the line number range 1-10:

   1 sed 10q         # Print lines 1-10 and then quit.
   2 sed '1,5d; 10q' # Print just lines 6-10 by filtering the first 5 then quitting after 10.

The d command stops sed from printing each line. This could alternatively have been done by passing sed the -n option and printing lines with the p command rather than deleting them with d. It makes no difference.

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

   1 # POSIX shell
   2 file=/etc/passwd
   3 range=10
   4 cur=1
   5 last=$(awk 'END { print NR }' < "$file") # count number of lines
   6 chunk=1
   7 while [ "$cur" -lt "$last" ]
   8 do
   9     endofchunk=$((cur + range - 1))
  10     sed -n -e "$cur,${endofchunk}p" -e "${endofchunk}q" "$file" > c"hunk.$(printf %04d "$chunk")"
  11     chunk=$((chunk + 1))
  12     cur=$((cur + range))
  13 done

The previous example uses POSIX arithmetic, which older Bourne shells do not have. In that case the following example should be used instead:

   1 # legacy Bourne shell; assume no printf either
   2 file=/etc/passwd
   3 range=10
   4 cur=1
   5 last=`awk 'END { print NR }' < "$file"` # count number of lines
   6 chunk=1
   7 while test "$cur" -lt "$last"
   8 do
   9     endofchunk=`expr $cur + $range - 1`
  10     sed -n -e "$cur,${endofchunk}p" -e "${endofchunk}q" "$file" > "chunk.$chunk"
  11     chunk=`expr "$chunk" + 1`
  12     cur=`expr "$cur" + "$range"`
  13 done

Awk can also be used to produce a more or less equivalent result:

   1 awk -v range=10 '{print > FILENAME "." (int((NR -1)/ range)+1)}' file

CategoryShell

-  ⇤ ← Revision 158 as of 2016-02-08 11:35:04 → 
  Size: 1973
  Editor: ormaaj
  Comment: maybe d instead of D?
+   ← Revision 162 as of 2022-04-19 12:13:19 → ⇥
  Size: 1999
  Editor: emanuele6
  Comment: fix file -> "$file"
-Deletions are marked like this.
+Additions are marked like this.
 Line 3:
-Some Unix systems provide the {{{split}}} utility for this purpose:
+POSIX specifies the {{{split}}} utility, which can be used for this purpose:
 Line 6:
-split --lines 10 --numeric-suffixes input.txt output-
+split -l 10 input.txt
 Line 24:
-last=$(wc -l < "$file") # count number of lines
+last=$(awk 'END { print NR }' < "$file") # count number of lines
 Line 26:
-while [ $cur -lt $last ]
+while [ "$cur" -lt "$last" ]
 Line 28:
-    endofchunk=$(($cur + $range - 1))
    sed -n -e "$cur,${endofchunk}p" -e "${endofchunk}q" "$file" > chunk.$(printf %04d $chunk)
    chunk=$(($chunk + 1))
    cur=$(($cur + $range))
+    endofchunk=$((cur + range - 1))
    sed -n -e "$cur,${endofchunk}p" -e "${endofchunk}q" "$file" > c"hunk.$(printf %04d "$chunk")"
    chunk=$((chunk + 1))
    cur=$((cur + range))
 Line 42:
-last=`wc -l < "$file"` # count number of lines
+last=`awk 'END { print NR }' < "$file"` # count number of lines
 Line 44:
-while test $cur -lt $last
+while test "$cur" -lt "$last"
 Line 47:
-    sed -n -e "$cur,${endofchunk}p" -e "${endofchunk}q" "$file" > chunk.$chunk
    chunk=`expr $chunk + 1`
    cur=`expr $cur + $range`
+    sed -n -e "$cur,${endofchunk}p" -e "${endofchunk}q" "$file" > "chunk.$chunk"
    chunk=`expr "$chunk" + 1`
    cur=`expr "$cur" + "$range"`