Matthew's Journal

"time" is a reserved keyword in bash, not a builtin as one might naively expect[1,2]. Even more amusingly, many UN*X systems also have /usr/bin/time which has rather less nice output.

This leads to some irritating edge-cases if you forget this (or didn't realise it in the first place). Consider:

bash-3.2$ time sleep 1

real    0m1.009s
user    0m0.000s
sys     0m0.002s
bash-3.2$ FOO=bar time sleep 1
        1.00 real         0.00 user         0.00 sys
bash-3.2$ time FOO=bar sleep 1

real    0m1.002s
user    0m0.000s
sys     0m0.002s

...and things only get worse if you actually start chaining things together...

bash-3.2$ time sleep 1 | time sleep 4
        4.00 real         0.00 user         0.00 sys

real    0m4.004s
user    0m0.001s
sys     0m0.005s

Not perhaps the best design decision ever...

[1] #chiark thinks this was to make it possible to time entire pipelines, although there would be several obvious idioms for doing that if time were a builtin
[2] See the "Pipelines" section in bash(1) for more details