Diff for "BashFAQ/011"

Differences between revisions 1 and 8 (spanning 7 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 1 as of 2007-05-02 22:55:48 → 
  Size: 620
  Editor: redondos
  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 3:
-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.
+The dirty (but not quick) way would be:
{{{
    sed -n ${n}p "$file"
}}}
-Line 5:
+Line 8:
-The following {{{sed}}} command line reads a file printing nothing (-n). At line $n the command "p" is run, printing it, with a "q" afterwards: quit the program.
+but this reads the whole input file, even if you only wanted the third line.
-Line 7:
+Line 10:
+This one avoids that problem:
-Line 11:
+Line 15:
-Another way, more obvious to some, is to grab the last line from a listing of the first n lines:
+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:
-Line 16:
+Line 22:
-Using awk:
+Another approach, using ["AWK"]:
-Line 18:
+Line 24:
-   awk 'NR==n{print;exit}' file
+   awk "NR==$n{print;exit}" file
-Line 20:
+Line 26:
+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
}}}