What's the fastest way to run n interations in BASH?

tl;dr Use for i in {0..1000}; it's the fastest.

Background

I happened across this post on stackoverflow.com. Then, I wondered: what's the fastest way I can run a command n times in BASH? After some quick googling, I was not satisfied with the results. So, I decided to test it for myself.

My System

• Linux 3.18.6-1-ARCH x86_64 GNU/Linux
• bash 4.3.33(1)-release
• seq (GNU coreutils) 8.23
  
  
• ruby 2.2.0p0
• benchmark-ips 2.1.1

Results

i/ps is calculated over a 5-second sample.

# n = 1000
       for {0..1000}:      150.5 (±25.3%) i/s
      for seq $(0 1000):   113.8 (±23.7%) i/s - 1.32x slower
       for (( ... )):       95.9 (±30.2%) i/s - 1.57x slower
     while read line:       76.2 (±23.6%) i/s - 1.97x slower
     while [[ ... ]]:       70.9 (±31.0%) i/s - 2.12x slower
       while [ ... ]:       64.9 (±26.6%) i/s - 2.32x slower

Breakdown

First of all, these are just my interpretations. I could be completely wrong, so feel free to let me know in the issues.

for {0..1000} is the fastest method out of the six. It is about 1.32x times faster than the runner up: for $(seq 0 1000)

Second place goes to: for $(seq 0 1000). With third going to: for (( .. )). The while loops were always slower than the for loops.

The while [[ ... ]] loop had the greatest standard deviation at ±31.0%, with for (( ... )) following close behind at ±30.2%. The rest of them have standard deviations between ±21.0% and ±26.6%.

It seems that BASH's internal [[ ]] operators are faster than [ ], which are just an alias for test. Over the long run, this gives [[ ]] a slight advantage in speed.