writing a string made up of a smaller string repeated many times

[miriam_e]

This was an interesting diversion today. I needed a way to construct a long string from a smaller one repeated many times, so I tried a few ways of my own devising and found many more on the net. There were some surprising ways to do this, but the really big surprises came when I decided to time them so as to work out which is the fastest. The winner is yes. That really surprised me. (Another big surprise was perl -- it ties for fastest.) The next two fastest are sed -E (extended regex) and plain sed.

NOTE: The time values I give below are the times to make a string repeating "test" 100,000 times.

EDIT: I have a late addition that uses perl. It surprisingly runs as fast as the yes/head/tr pipeline. I've added it at the bottom.

Here is my list of solutions:

yes is a command that endlessly prints out a string

yes "test" | head -n 10 | tr "\n" " " ; echo

0.044 seconds

A tricky way to use printf

printf 'test %.0s' {1..10} ; echo

0.190 seconds

printf to a variable

printf -v testvar 'test %.0s' {1..10}

0.169 seconds

A slightly different way to printf to a variable

printf -v testvar '%s ' test$_{1..10}

0.194 seconds

An echo {} hack.It requires that $nothing1 $nothing2 $nothing3 ... be non-existent variables.

echo test$nothing{1..10}

0.217 seconds

simple {} sequence loop

for i in {1..10} ; do echo -n "test " ; done ; echo

1.482 seconds

two simple seq loops

for i in $(seq 10) ; do echo -n "test " ; done ; echo

1.617 seconds

for i in `seq 10` ; do echo -n "test " ; done ; echo

1.367 seconds

simple c-style loop

n=10 ; for (( c=1; c<=n; c++)) ; do echo -n "test " ; done ; echo

2.130 seconds

a weird one

echo 'test'{,,,,,,,,,}

using awk for part

seq 10 | awk '{printf "test "}'; echo

0.769 seconds

awk only

awk 'BEGIN{for (n=0; n<10; n++) printf "test "; print ""}'

0.880 seconds

using sed for part

seq 10 | sed -E 's/.+/test/' | tr '\n' ' ' ; echo

0.089 seconds

or

seq 10 | sed 's/.*/test/' | tr '\n' ' ' ; echo

0.096 seconds

or

seq 10 | sed -z 's/[^\n]*\n/test/g' ; echo

0.173 seconds

using perl

perl -e 'print "test " x 10; print "\n"'

0.046 seconds