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Kusalananda ♦
Kusalananda ♦
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#!/bin/sh

generate_data () {
        shuf -i 0-1000 -n 10 -r
}

print_maximum () {
        awk 'NR == 1 || m < $0 { m = $0 } END { print m }'
}

exec 3>&1
maximum=$(
    generate_data |
    tee /dev/fd/3 |
    print_maximum
)
exec 3>&-

printf 'maximum = %d\n' "$maximum"

This passes some random numbers through tee, duplicating them to file descriptor 3 and to the standard output of tee. The standard output is read by print_maximum, which finds and outputs the largest number among the ones generated.

File descriptor 3 is initially opened as copy of the shell's standard output stream (with exec 3>&1), which means that when tee writes to it (by writing to /dev/fd/3), the data appears on the shell's standard output. That file descriptor is later closed (with exec 3>&-).

Note that the script uses /bin/sh as it does not need to use any bash-isms. With bash though, you'd be guaranteed that /dev/fd/3 was usable as file descriptor 3, and not reliant on that path being provided by the system.

Example run:

$ sh script
918
787
290
998
737
1000
845
374
497
809
maximum = 1000

To show that all output is generated on the script's standard output, I can show that it's possible to grep the generated data:

$ sh script | grep -F 0
100
807
maximum = 807

$ sh script | grep -F 0
440
207

#!/bin/sh

generate_data () {
        shuf -i 0-1000 -n 10 -r
}

print_maximum () {
        awk 'NR == 1 || m < $0 { m = $0 } END { print m }'
}

exec 3>&1
maximum=$(
    generate_data |
    tee /dev/fd/3 |
    print_maximum
)
exec 3>&-

printf 'maximum = %d\n' "$maximum"

This passes some random numbers through tee, duplicating them to file descriptor 3 and to the standard output of tee. The standard output is read by print_maximum, which finds and outputs the largest number among the ones generated.

File descriptor 3 is initially opened as copy of the shell's standard output stream (with exec 3>&1), which means that when tee writes to it (by writing to /dev/fd/3), the data appears on the shell's standard output. That file descriptor is later closed (with exec 3>&-).

Note that the script uses /bin/sh as it does not need to use any bash-isms.

Example run:

$ sh script
918
787
290
998
737
1000
845
374
497
809
maximum = 1000

To show that all output is generated on the script's standard output, I can show that it's possible to grep the generated data:

$ sh script | grep -F 0
100
807
maximum = 807

$ sh script | grep -F 0
440
207

#!/bin/sh

generate_data () {
        shuf -i 0-1000 -n 10 -r
}

print_maximum () {
        awk 'NR == 1 || m < $0 { m = $0 } END { print m }'
}

exec 3>&1
maximum=$(
    generate_data |
    tee /dev/fd/3 |
    print_maximum
)
exec 3>&-

printf 'maximum = %d\n' "$maximum"

This passes some random numbers through tee, duplicating them to file descriptor 3 and to the standard output of tee. The standard output is read by print_maximum, which finds and outputs the largest number among the ones generated.

File descriptor 3 is initially opened as copy of the shell's standard output stream (with exec 3>&1), which means that when tee writes to it (by writing to /dev/fd/3), the data appears on the shell's standard output. That file descriptor is later closed (with exec 3>&-).

Note that the script uses /bin/sh as it does not need to use any bash-isms. With bash though, you'd be guaranteed that /dev/fd/3 was usable as file descriptor 3, and not reliant on that path being provided by the system.

Example run:

$ sh script
918
787
290
998
737
1000
845
374
497
809
maximum = 1000

To show that all output is generated on the script's standard output, I can show that it's possible to grep the generated data:

$ sh script | grep -F 0
100
807
maximum = 807

$ sh script | grep -F 0
440
207
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Source Link
Kusalananda ♦
Kusalananda ♦
  • 356.2k
  • 42
  • 737
  • 1.1k
#!/bin/sh

generate_inputgenerate_data () {
        shuf -i 0-1000 -n 10 -r
}

find_maximumprint_maximum () {
        awk 'NR == 1 || m < $0 { m = $0 } END { print m }'
}

exec 3>&1
maximum=$(
    generate_inputgenerate_data |
    tee /dev/fd/3 |
    find_maximumprint_maximum
)
exec 3>&-

printf 'maximum = %d\n' "$maximum"

This passes some random numbers through tee, duplicating them to file descriptor 3 and to the standard output of tee. The standard output is read by find_maximumprint_maximum, which finds and outputs the largest number among the ones generated.

File descriptor 3 is initially opened as copy of the shell's standard output stream (with exec 3>&1), which means that when tee writes to it (by writing to /dev/fd/3), the data appears on the shell's standard output. The That file descriptor is later closed (with exec 3>&-).

Note that the script uses /bin/sh as it does not need to use any bash-isms.

Example run:

$ sh script
918
787
290
998
737
1000
845
374
497
809
maximum = 1000

To show that all output is generated on the script's standard output, I can show that it's possible to grep the generated data:

$ sh script | grep -F 0
100
807
maximum = 807

$ sh script | grep -F 0
440
207

#!/bin/sh

generate_input () {
        shuf -i 0-1000 -n 10 -r
}

find_maximum () {
        awk 'NR == 1 || m < $0 { m = $0 } END { print m }'
}

exec 3>&1
maximum=$(
    generate_input |
    tee /dev/fd/3 |
    find_maximum
)
exec 3>&-

printf 'maximum = %d\n' "$maximum"

This passes some random numbers through tee, duplicating them to file descriptor 3 and to the standard output of tee. The standard output is read by find_maximum, which finds and outputs the largest number among the ones generated.

File descriptor 3 is initially opened as copy of the shell's standard output stream (with exec 3>&1), which means that when tee writes to it (by writing to /dev/fd/3), the data appears on the shell's standard output. The file descriptor is later closed (with exec 3>&-).

Note that the script uses /bin/sh as it does not need to use any bash-isms.

Example run:

$ sh script
918
787
290
998
737
1000
845
374
497
809
maximum = 1000

#!/bin/sh

generate_data () {
        shuf -i 0-1000 -n 10 -r
}

print_maximum () {
        awk 'NR == 1 || m < $0 { m = $0 } END { print m }'
}

exec 3>&1
maximum=$(
    generate_data |
    tee /dev/fd/3 |
    print_maximum
)
exec 3>&-

printf 'maximum = %d\n' "$maximum"

This passes some random numbers through tee, duplicating them to file descriptor 3 and to the standard output of tee. The standard output is read by print_maximum, which finds and outputs the largest number among the ones generated.

File descriptor 3 is initially opened as copy of the shell's standard output stream (with exec 3>&1), which means that when tee writes to it (by writing to /dev/fd/3), the data appears on the shell's standard output. That file descriptor is later closed (with exec 3>&-).

Note that the script uses /bin/sh as it does not need to use any bash-isms.

Example run:

$ sh script
918
787
290
998
737
1000
845
374
497
809
maximum = 1000

To show that all output is generated on the script's standard output, I can show that it's possible to grep the generated data:

$ sh script | grep -F 0
100
807
maximum = 807

$ sh script | grep -F 0
440
207
Source Link
Kusalananda ♦
Kusalananda ♦
  • 356.2k
  • 42
  • 737
  • 1.1k

#!/bin/sh

generate_input () {
        shuf -i 0-1000 -n 10 -r
}

find_maximum () {
        awk 'NR == 1 || m < $0 { m = $0 } END { print m }'
}

exec 3>&1
maximum=$(
    generate_input |
    tee /dev/fd/3 |
    find_maximum
)
exec 3>&-

printf 'maximum = %d\n' "$maximum"

This passes some random numbers through tee, duplicating them to file descriptor 3 and to the standard output of tee. The standard output is read by find_maximum, which finds and outputs the largest number among the ones generated.

File descriptor 3 is initially opened as copy of the shell's standard output stream (with exec 3>&1), which means that when tee writes to it (by writing to /dev/fd/3), the data appears on the shell's standard output. The file descriptor is later closed (with exec 3>&-).

Note that the script uses /bin/sh as it does not need to use any bash-isms.

Example run:

$ sh script
918
787
290
998
737
1000
845
374
497
809
maximum = 1000