bash script write executing time in a file

Question

I need to write the time taken to execute this command in a txt file: ``` time ./program.exe ``` How can I do in bash script? I try with `>> time.txt` but that doesn't work (the output does not go to file and does go to the screen).

Accepted Answer

Getting `time` in `bash` to write to a file is hard work. It is a `bash` built-in command. (On Mac OS X, there's an external command, `/usr/bin/time`, that does a similar job but with a different output format and less recalcitrance.)

You need to use:

```
(time ./program.exe) 2> time.txt
```

It writes to standard error (hence the `2>` notation). However, if you don't use the sub-shell (the parentheses), it doesn't work; the output still comes to the screen.

Alternatively, and without a sub-shell, you can use:

```
{ time ./program.exe; } 2> time.txt
```

Note the space after the open brace and the semi-colon; both are necessary on a single line. The braces must appear where a command could appear, and must be standalone symbols. (If you struggle hard enough, you'll come up with `...;}|something` or `...;}2>&1`. Both of these identify the brace as a standalone symbol, though. If you try `...;}xyz`, the shell will (probably) fail to find a command called `}xyz`, though.)

I need to run more command in more terminal. If I do this:

```
 xterm -xrm '*hold: true' -e (time ./Program.exe) >> time.exe & sleep 2
```

it doesn't work and tells me `Syntax error: "(" unexpected`. How do I fix this?

You would need to do something like:

```
xterm -xrm '*hold: true' -e sh -c "(time ./Program.exe) 2> time.txt & sleep 2"
```

The key change is to run the shell with the script coming from the argument to the `-c` option; you can replace `sh` with `/bin/bash` or an equivalent name. That should get around any 'Syntax error' issues. I'm not quite sure what triggers that error, though, so there may be a simpler and better way to deal with it. It's also conceivable that `xterm`'s `-e` option only takes a single string argument, in which case, I suppose you'd use:

```
xterm -xrm '*hold: true' -e 'sh -c "(time ./Program.exe) 2> time.txt & sleep 2"'
```

You can manual bash `xterm` as well as I can.

I'm not sure why you run the timed program in background mode, but that's your problem, not mine. Similarly, the `sleep 2` is not obviously necessary if the `hold: true` keeps the terminal open.

bash script write executing time in a file

Solution

Problem