how to check if a word exists on a web page

Question

In this example script below

keyword="google"
var1="wget -qO- https://www.google.com"
echo "$var1"
var2="[test -z "$var1 | grep $keyword"]"
echo $var2

I get

 wget -qO- https://www.google.com

but var2 is empty.

In this script

keyword="google"
var1="wget -qO- https://www.google.com"
echo " $var1"
var2="[test -z "https://www.google.com" | grep "google"]"
echo $var2

I get

wget -qO- https://www.google.com
[test -z https://www.google.com | grep google]

I've tried any number of permutations of single and double quotes but I cannot get the test statement to evaluate.

How can I actually get a test command to evaluate in a script? And How can I use variables in a 'test' command?

See [How do I set a variable to the output of a command in Bash?](https://stackoverflow.com/questions/4651437/how-do-i-set-a-variable-to-the-output-of-a-command-in-bash) But in the case of a test expression (which starts with `[` or `test`, but not both, and has spaces between each element) it doesn't produce output, it produces an [exit status](https://stackoverflow.com/questions/7248031/meaning-of-dollar-question-mark-in-shell-scripts). BTW, [shellcheck.net](https://www.shellcheck.net) is good at pointing out common mistakes (although it doesn't catch all of them). — Gordon Davisson, Nov 21 '20 at 17:33

Jorengarenar · Accepted Answer · 2020-11-21T17:44:14.533

Variables

var2="[test -z "$var1 | grep $keyword"]"

Let's see what is and what is not quoted here:

"[test -z " - first quoted atom, so far good
$var1 - variable gets expanded and concatenated to previous string
| grep $keyword - first problem, there are no quotes where are whitespaces, Bash doesn't know what to do with it (it thinks those are arguments and tries to pipe variable assignation to grep)
"]" - it appends it to $keyword, which is grep argument

So Bash first executes var2="[test -z "$var1 then pipes it to grep $keyword"]"

Possible solutions:

This is in regards of variables.

To evaluate text string as shell command (although you should avoid doing that at all), you simply use eval command:

eval "$var2"

or just variable alone:

"$var2"

Evaluating var2 makes no sense as the code contained inside is simply invalid. Making it a variable is needless at all.

You simply need to do:

keyword="google"
var1="wget -qO- https://www.google.com"

if test -z "$($var1 | grep $keyword)"; then
    echo "Not found word"
fi

Why was code in var2 invalid:

square brackets - [ is an alias for test. Writing [ test is (almost) equivalent to test test. The difference between test and [ is that in case of [ you need to end command with ]
no spaces after [ and before ]
when you want to use output of a command, you need to capture it using $(command)

thaank you so much, both of you. I felt like I had fallen through the looking glass and was in wonderland. — aquagremlin, Nov 21 '20 at 20:50