CODEWITHSUNDEEP
bashif-statement
linkyndy
linkyndy

Reputation: 17920

If statement in Bash creates weird 0 file

When I run the following command:

if [ $(vboxmanage list vms | grep -c "all-in-one-1.2.7-wizard") > 0 ]; then
    echo 'yes'
else 
    echo 'no'
fi

a 0 file is created in the current directory:

$ ll
...
-rw-rw-r--  1 abc abc     0 Nov 19 17:33 0

Any idea why is this happening?

Upvotes: 0

Views: 49

Answers (1)

fedorqui
fedorqui

Reputation: 290025

You are not doing an integer comparison, but redirecting the output of the command $() into 0, so a file with 0 name is created.

Also, the current "resolution" of the if-condition is based on the result of the execution of the condition. If it is successful, then it executes the condition.

Instead, use -gt (greater than):

if [ $(vboxmanage list vms | grep -c "all-in-one-1.2.7-wizard") -gt 0 ]; then
                                                                 ^^
    echo 'yes'
else
    echo 'no'
fi

You can make sure this is the behaviour by doing >7 or whatever and see a file 7 (or whatever) gets created.

When would the else condition be executed? If you couldn't redirect:

$ [ $(ls /root) > 3 ] && echo "yes" || echo "no"
ls: cannot open directory /root: Permission denied
no

See Numeric comparison for the list of all the possible integer comparisons.

Upvotes: 6

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