Diff for "BashFAQ/011"

Differences between revisions 5 and 8 (spanning 3 versions)

How can I print the n'th line of a file?

The dirty (but not quick) way would be:

    sed -n ${n}p "$file"

but this reads the whole input file, even if you only wanted the third line.

This one avoids that problem:

    sed -n "$n{p;q;}" "$file"

At line $n the command "p" is run, printing it, with a "q" afterwards: quit the program.

Another way, more obvious to some, is to grab the last line from a listing of the first n lines:

   head -n $n $file | tail -n 1

Another approach, using ["AWK"]:

   awk "NR==$n{print;exit}" file

If you want more than one line, it's pretty easy to adapt any of the previous methods:

   x=3 y=4;
   sed -n "$x,${y}p;${y}q;" "$file"                # Print lines $x to $y; quit after $y.
   head -n $y "$file" | tail -n $(($y - $x + 1))   # Same
   awk "NR>=$x{print} NR==$y{exit}" "$file"        # Same

Using nl(1) (and grep(1) (and cut(1))):

   nl -b a file | grep '^  *<number of line>\W' | cut -f 2

-  ⇤ ← Revision 5 as of 2007-09-21 01:53:10 → 
  Size: 1042
  Editor: p54884242
  Comment:
+   ← Revision 8 as of 2007-10-16 13:51:05 → ⇥
  Size: 1057
  Editor: p54BFE162
  Comment: make regex work (10 would match 102 as well). although only sed really makes sense here, using nl is still way less pointless than pr!
-Deletions are marked like this.
+Additions are marked like this.
 Line 30:
+   x=3 y=4;
-Line 32:
+Line 33:
-   awk 'NR>=$x{print} NR==$y{exit}' "$file"        # Same
+   awk "NR>=$x{print} NR==$y{exit}" "$file"        # Same
-Line 35:
+Line 36:
-Using cat(1) (and grep(1) (and cut(1))):
+Using nl(1) (and grep(1) (and cut(1))):
-Line 38:
+Line 39:
-   cat -n file | grep '^  *<number of line>' | cut -f 2
+   nl -b a file | grep '^  *<number of line>\W' | cut -f 2