Bash compare command to string [duplicate]

Question

I want to run a command and compare the result the command produces to another value, and then either echo 0 or 1.

For example (in pseudocode) something along the lines of:

if ($(app --version) == "1.2.3") then echo 1" else echo "0"

Preferably the actual command output from app --version would be suppressed so that only 0 or 1 is written to stdout, depending on the result.

How can I do this with bash? Is there a quick one liner for that?

@NicoHaase I tried something like $(app --version) -eq "1.2.3" && echo "0" || echo "1", but that results in the version being interpreted as a command. Also the output itsn't surpressed. I am not to familiar with the bash scripting syntax. I guess for surpressing the output of the command one could pipe to /dev/null ..? but first i gotta get the actual comparison to work — n00b.exe
– n00b.exe, Commented Nov 26, 2020 at 13:08
Put the result of cmd into double quotes and brackets. e.g. [ "$(app --version)" == "1.2.3" ] && echo 1 || echo 0 — Milan Dufek
– Milan Dufek, Commented Nov 26, 2020 at 13:09

imthor · Accepted Answer · 2020-11-26 14:54:00Z

1

Does these work?

$ if [ "$(<path>/app --version)" = "1.2.3" ]; then echo 0; else echo 1; fi
0

$ [ "$(<path>/app --version)" = "1.2.3" ] && echo 0 || echo 1
0

edited Nov 26, 2020 at 14:54

answered Nov 26, 2020 at 14:07

imthor

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4 Comments

n00b.exe Over a year ago

No, unfortunately not. I still get the same error I described in the comments: i.imgur.com/LxTVIXo.png EDIT: Running it directly in bash makes it work. Weird, not sure why it does not work in zsh.

imthor Over a year ago

I didn't know you were using zsh. == is not standard, the POSIX way is =, make that change in the above comparison and it should work in zsh as well

user1934428 Over a year ago

@n00b.exe : You asked for a bash solution, so you got a bash solution. If you want one in zsh, or FORTRAN, or whatever, specify so in your question please.

n00b.exe Over a year ago

@user1934428 Yea, I should have made that more clear.

user1934428 · Accepted Answer · 2020-11-26 15:27:24Z

1

if [[ $(app --version) == 1.2.3 ]]
then
  echo 0
else
  echo 1
fi

would work in bash (and in zsh and ksh, in case this is important).

answered Nov 26, 2020 at 15:27

user1934428

22.8k9 gold badges57 silver badges108 bronze badges

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