built-in time not formatting correctly in bash

Question

I am writing a script for competitive programming judging and here is part of the bash script:

#!/bin/bash
TIMEFORMAT=%S
if [ $1 = "-cpp" ]; then
    output1=$(g++ -std=c++17 -O2 -Wall -fsanitize=address -lm -s -x c++ b.cpp && ./a.out < input1)
    expected1=$(< output1)
    time1=$(time g++ -std=c++17 -O2 -Wall -fsanitize=address -lm -s -x c++ b.cpp && ./a.out < input1)
    if [[ -z "$expected" ]]; then
        echo "Test Case #1 - Passed! Time: ${time1} sec"
    elif [ $output1 = $expected1 ]; then
        echo "Test Case #1 - Passed."
    else
        echo "Test Case #1 - Failed (check 'dump1.log' for details)."
    fi
fi

The output for the C++ program is 15. The output of the bash script is:

0.172
Test Case #1 - Passed! Time: 15 sec

It prints the time output above the actual point of concatenation. And in the place of concatenation, it prints the actual C++ output. I am extremely new to bash so I don't know what is going on.

The output from time (which is your shell's builtin time function, not /usr/bin/time) is going to standard error, while your time=$(time g++ ...) is capturing the C++ program's ordinary output. I don't see where $expected gets defined at all. — steeldriver, Jun 08 '21 at 13:38
Always paste your script into https://shellcheck.net, a syntax checker, or install shellcheck locally. Make using shellcheck part of your development process. — waltinator, Jun 08 '21 at 13:39
... (cont.) see for example How to capture stderr of a bash keyword (e.g. time)? and more generally How to measure time of program execution and store that inside a variable — steeldriver, Jun 08 '21 at 13:42
I changed it so that I don't need /usr/bin/time anymore, is there still a method of formatting built in time? — VJZ, Jun 08 '21 at 14:08
@VJZGamingHD you have successfully formatted the builtin time (hence why you get 0.172 instead of the default real xxx / user xxx / sys xxx). What you have not done is captured it in the time1 variable, for the reasons explained in the linked answers. — steeldriver, Jun 08 '21 at 14:39
@steeldriver For some reason doing 2>&1 1>/dev/null worked. Can you explain why I have to append that to the end of the command in the solutions so I can mark it as correct? — VJZ, Jun 08 '21 at 15:06

score -3 · Answer 1 · answered Jun 08 '21 at 13:39

-3

By simply calling time, you're making use of the bash builtin. Check this with type -a time.

To use the time program, use the full path, /usr/bin/time.

Read man time bash.

answered Jun 08 '21 at 13:39

waltinator

4,865

1

Why is man time relevant here? That gives the manual for the binary /usr/bin/time (or whatever is installed), not for the builtin. Did you mean "read help time"? And how is this answering the OP's question about the output they are seeing? – terdon Jun 08 '21 at 13:48

built-in time not formatting correctly in bash

1 Answers1