如何在循环中打印东西到控制台，以便unix grep可以与它交互？

Question

How to print stuff in a loop to console, so that UNIX grep can interact with it ? I made a console php tool for parsing some data. I am in need of printing some data to console.

public function printAlerts()
{
    $alertLinks = $this->parser->alertLinks($this->mc->listAlerts());

    $idSize = $alertLinks['sizeArray']['id'];
    $dateSize = $alertLinks['sizeArray']['date'];
    $nameSize = $alertLinks['sizeArray']['name'];

    $margin = 5;

    foreach ($alertLinks['alertArray'] as $alert)
    {
        $this->printColumn($alert['id'], $idSize, $margin);
        $this->printColumn($alert['date'], $dateSize, $margin);
        $this->printColumn($alert['name'], $nameSize, $margin);
        echo "
";
    }
}

private function printColumn($data, $space = 0, $margin = 0)
{
    echo $data;
    $len = ($space - strlen($data)) + $margin;

    for ($i = 0; $i < $len; $i++)
    {
        echo ' ';
    }

    return;
}

I would like to interact with this printed data with Unix grep command. For example:

php script.php -list | grep stuff

Using this code all data gets printed in the console, but grep can not filter it, why? how to make grep filter the text ?

Answer 1

Consider this demonstration:

<?php
$words = array( "column", "igloo", "magenta", "turnip", "adlib", "stuff");

foreach( $words as $word){
        printf("%8s
", $word );
}

We can filter out the line containing stuff just fine.

$ php ./t.php | grep 'stuff'
   stuff

If instead we write to stderr, we must filter a bit diferently:

<?php
$words = array( "column", "igloo", "magenta", "turnip", "adlib", "stuff");

foreach( $words as $word){
        fprintf(STDERR,"%8s
", $word );
}

Since grep reads from stdin, we need to make sure we redirect stderr to stdout:

php ./t.php 2>&1 | grep stuff

Finally, if you want to make sure you don't get stdout too, you could switch them:

php ./t.php 2>&1 1>&2 | grep stuff

Or just discard the data originally written to stdout:

php ./t.php 2>&1 >/dev/null | grep stuff

Hope it helps!