One liner if-else not working as intended [duplicate]

Question

I made a simple script on WSL for windows 11 to mount my pen drive. The default option is to mount it from D:, and I can specify as an argument if the pen drive is in another place.

The script is like this:

#! /bin/bash [[ $# -eq 0 ]] && sudo mount -t drvfs D: /pen || sudo mount -t drvfs ${1}: /pen [[ $? == 0 ]] && echo "Good" || echo "Bad"

It works when the pen drive is connected on port D:, but when there is no pen drive connected, the first command executes both sides of the OR.

I am expecting it to execute on the same basis of al if-else statement. If the condition is true, it executes the left side, and if it is false, it executes the right side.

The && ... || trick is not equivalent to an if ... then ... else ... fi. Don't use it, it just doesn't work. See BashPitfalls #22 and "Can't increment variable in bash shorthand if else condition". — Gordon Davisson
– Gordon Davisson, Commented May 31, 2023 at 9:30
I would just use if...else at this point, but if you insist on keeping this form, you can do: A && { B; true; } || C — Verpous
– Verpous, Commented May 31, 2023 at 10:13
Actually, in this case you could skip the conditional entirely, and use an alternate value substitution to make "D" the default parameter: sudo mount -t drvfs "${1:-D}:" /pen — Gordon Davisson
– Gordon Davisson, Commented May 31, 2023 at 10:14
@Pau: Of course you can always write a normal if....fi into a single line, if you want. Statements are separated by either newlines or semicolons. — user1934428
– user1934428, Commented May 31, 2023 at 11:19
Just remember that A && B || C does not equal if A then B else C fi, it equals if A then if ! B then C fi; else C fi. — Ed Morton
– Ed Morton, Commented May 31, 2023 at 12:36

Taras Khalymon · Accepted Answer · 2023-05-31 15:06:56Z

This construction (so called one-line if statement) uses executable part as a condition assuming that it's true. But if "true" part returns false, second part will also be executed.

Here's the example:

[[ 0 == 0 ]] && (echo "Good"; exit 1) || echo "Bad"

Condition is true, but executable part after it returns false (exit 1), so [[ 0 == 0 ]] && (echo "Good"; exit 1) part is false and we should check another condition of || operator.

As a result, we are executing both true and false parts.

If you need to fit it into a single line, you can add || true to "true" part:

[[ 0 == 0 ]] && (echo "Good" || true) || echo "Bad"

In this case, even if echo "Good" returns false, the whole "true" part will return true and false second part of || will not be checked.

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