How to check condition for shell script same as javascript

Question

I tried check shell script condition for same as javascript but is this not working

javascript

const data = "string";
if (data) {
   console.log("condition true");
}

shell script

# /bin/bash

data="string"
name=test
age=24

if($data); then
echo "condition satisfied"
fi

if [ "$data" && "$name" && "$age" ]; then
    echo "condition satisfied"
fi

check here

Barmar · Accepted Answer · 2020-01-09 03:03:45Z

1

Use the test command, usually written as [.

#!/bin/bash

data="string"
if [ -n "$data" ]; then
    echo "condition satisfied"
fi

For multiple conditions use && between the tests.

if [ -n "$data" ] && [ -n "$name" ] && [ -n "$age" ]

edited Jan 9, 2020 at 3:03

answered Jan 9, 2020 at 2:53

Barmar

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6 Comments

Mark Reed Over a year ago

Note that if the string is literally just the word string, you don't need the double quotes; you only need those if the value has spaces or certain other special characters in it (in which case single quotes would be safer). Since you tagged this bash, note that you can also remove the double quotes around $data if you use double [[...]]instead of single [...]. That doesn't work in all sh-compatible shells and is not part of the POSIX spec for such, though.

Saran Raj Over a year ago

Thanks barmar, but I have another doubt is how check multiple condition in single condition help for us

Barmar Over a year ago

The literal assignment is presumably just an example, in a real application the variable would be set dynamically. And I prefer to quote variables all the time, it's easier than trying to remember when they can be omitted. @MarkReed

Barmar Over a year ago

@SaranRaj I think you need to learn shell scripting, this isn't a programming school.

Saran Raj Over a year ago

Yes barmar I am beginner for this.

|

user1934428 · Accepted Answer · 2020-01-09 08:46:46Z

Assuming that you want to see the equivalent to console log printed to stdout, the following will do:

[ "$data" ] && echo "condition satisfied"

or equivalently

test "$data" && echo "condition satisfied"

(the double quotes are needed for the case data contains a space), or, provided you have bash (since you tagged the question for bash and for shell),

[[ $data ]] && echo "condition satisfied"

Here the quotes are not needed.

All variants test whether the variable data contains a non-empty string, and if this is the case, it prints the message.

This is of course not exactly the same as if(data) in JavaScript, because in JavaScript, if data had the value 0, the condition would be considered false. You can emulate this behvaviour in shell too, but it gets more cumbersome.

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