Entries Tagged as 'bash'

The tricky little "httpd -M" command

A project I'm doing requires that I write a BASH shell script that checks what modules are installed in Apache (to make sure some requirements are met before an install is attempted), however, I had a HECK OF A TIME figuring out how to script the checking of the httpd -M command (the command that shows the installed Apache modules). I was tring to run the following on a CentOS 5 server:

# httpd -M | grep -c perl

And the results of the command were not being piped to grep. Instead, the results were being sent to the screen. Irritating! There's clearly a pipe character there. I kept thinking I was writing the command wrong or something. I tried the command on my Ubuntu desktop, and lo and behold it worked just fine:

$ sudo apache2ctl -M | grep -c perl

apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1 for ServerName
Syntax OK
1

Broken ApacheThe "1" was the result I was looking for, because I knew mod_perl was installed.

Long story short, for some reason the CentOS 5 version of Apache sends the "httpd -M" results to stderr, rather then stdout. I have no freaking idea why it does this, because that's not error data. It seems like a bug in the HTTPD executable. The end result was that I needed to write my command as follows:

# httpd -M  2>&1 | grep -c perl

1

The 2>&1 sends the stderr data to stdout which is what the pipe character sends to the grep command.

How annoying. For the record:

# httpd -v

Server version: Apache/2.2.3
Server built:   Oct 20 2011 17:00:12

Hope this helps someone avoid the frustration and confusion I went through finding it.

BASH - Generate a Random String

In a recent project, I needed a function that would generate a random string for me. In my case, I was creating a random file name to store some data, but there are other uses as well, so I am posting the BASH code here in the hope that it will help others out ther eon the net writing BASH scripts and need a good random string function:

#!/bin/bash
function randomString {
        # if a param was passed, it's the length of the string we want
        if [[ -n $1 ]] && [[ "$1" -lt 20 ]]; then
                local myStrLength=$1;
        else
                # otherwise set to default
                local myStrLength=8;
        fi

        local mySeedNumber=$$`date +%N`; # seed will be the pid + nanoseconds
        local myRandomString=$( echo $mySeedNumber | md5sum | md5sum );
        # create our actual random string
        myRandomResult="${myRandomString:2:myStrLength}"
}

randomString 10;
echo $myRandomResult;