Repeat each line multiple times

Question

Would like to have each line in a file repeated a fixed number of times.

e.g. have each line repeated four times:

a
b
c

becomes:

a
a
a
a
b
b
b
b
c
c
c
c

I've done some searching, and there are a lot of questions and answers along the lines of doing the reverse, e.g. merging duplicate lines into single lines, and maybe a few about doubling lines by printing them again.

It would be easy to do this in C, but I wish I knew more about the native commands so I wouldn't have to resort to these kinds of one-off throw-aways all the time.

Answer 1

I wonder if this is turning into a golf match:

sed 'p;p;p' 
awk '1;1;1;1' 
perl -lpE 'say;say;say'   # if Paul McCartney and Michael Jackson were hackers...

Explanation:

sed's p command is to print the current line. The default behaviour is to print the current line just before moving to the next line (that's why sed has -n to allow you to turn it off). Some older seds don't have the semicolon (I think) so it's possible you might have to do sed -e p -e p -e p

Awk works with condition {action} pairs. If the action is omitted, the default is to print the current line if the condition returns true. Awk, like many C-like languages, treats 1 as true. (For completeness, if the condition is omitted, the action will be executed for each record.)

Many perl functions take advantage of the "default" variable. This one-liner is equivalent to (on perl 5.16):

$ perl -MO=Deparse -lpE 'say;say;say'
BEGIN { $/ = "\n"; $\ = "\n"; }
use feature 'current_sub', 'evalbytes', 'fc', 'say', 'state', 'switch', 'unicode_strings', 'unicode_eval';
LINE: while (defined($_ = <ARGV>)) {
    chomp $_;
    say $_;
    say $_;
    say $_;
}
continue {
    die "-p destination: $!\n" unless print $_;
}

Answer 2

• Perl:

  perl -ne 'for$i(0..3){print}' file
  

  and I have to add this one posted as a comment by @derobert because it is just cool:

  perl -ne 'print "$_" x4'
  

• awk and variants:

  awk '{for(i=0;i<4;i++)print}' file
  

• bash

  while read line; do for i in {1..4}; do echo "$line"; done; done < file
  

Answer 3

sed -n '{p;p;p;p;}' file

awk '{print;print;print;print;}' file

Answer 4

You can do this without requiring sed, perl, or awk.

$ for i in `cat <file>` ; do seq <#> <#> | xargs -i -- echo $i ; done

or using a while loop:

$ while read i ; do seq <#> <#> | xargs -i -- echo $i ; done < <file>

Examples

for loop

$ for i in `cat sample.txt` ; do seq 1 3 | xargs -i -- echo $i ; done
a
a
a
b
b
b
c
c
c

while loop

$ while read i; do seq 1 2| xargs -i -- echo $i;done < sample.txt
a
a
b
b
c
c

Answer 5

Using purely shell:

repeats=4
while read line; do yes $line|head --lines=$repeats; done < infile > outfile

Answer 6

This might work for you (GNU sed):

sed 'h;:a;s/[^\n]\+/&/4;t;G;ba' file

Will repeat each line 4 times.

Or if you prefer:

sed 'h;:a;s/\n/&/3;t;G;ba' file

Where you repeat each line 3 more times.

Answer 7

@potong 's answer does not work with empty lines, replacing \+ with * should fix it:

sed 'h;:a;s/[^\n]*/&/4;t;G;ba' file