1

Say I have a file (php as it happens), with a number of variable declarations:

$dbuser = 'fred';
$dppass = 'abc123';
$dhhost = '127.0.0.1';

What I want to do from a BASH script, is parse this file, identify the variables I need, and read their values into variables I can access from my BASH script.

Obviously, the above file being PHP, has other lines that I'm not interested in.

I can extract the info I need from the bash shell using the following command:

grep \$dbuser config.php.inc | grep -Po "\'.*\'" | cut -d \' -f 2

which neatly returns

fred

But when I try to add this to a bash script to put the output into a variable using backticks, as follows:

dbuser=`grep \$dbuser config.php.inc | grep -Po "\'.*\'" | cut -d \' -f 2`

my BASH script hangs at this point.

Why is this hanging, or, is there a better way of doing what I'm trying to achieve?

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4 Answers 4

Reset to default
2

Try it this way:

dbuser=$(grep \$dbuser config.php.inc | grep -Po "\'.*\'" | cut -d \' -f 2)

The reason this works and the backticks did not is in the way $(command) handles quoting vs. how the old style backticks handles quoting.

In other words, the following backtick command would have worked just as well:

dbuser=`grep '$dbuser' config.php.inc | grep -Po "'.*'" | cut -d"'" -f 2`
  1. Used single quotes to enclose $dbuser since single quotes means use the literal text rather than interpolate it as a shell variable.
  2. Removed the escaping from .* since it is not needed.
  3. Removed the escaping from the cut command since it is not needed.

BTW, this would have worked as well:

dbuser=`grep '$dbuser' config.php.inc | grep -Po "\'.*\'" | cut -d \' -f 2`

Additionally, the $(command) syntax is in general the best approach whenever possible. Use `` only for portability reasons if you must support a platform that is absolutely known to not support $(command). This is IMHO very rare, so the rule of thumb is to lean towards $(command) from the start.

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4 Comments

Can you explain why this works? I think it does work - but it is very subtle.
Is this a better method than using backticks?
Essentially, yes, $(command) is the better and more modern approach. Use backticks only when you need to support a platform that is known to not support $(command) which is rare these days. Backticks have issues with less-than-trivial quoting and really fall down when you need to support multiple levels of nested commands. $(command) handles this well.
Many thanks for the explanation, I wasn't aware of this, and have just always used backticks. I wish I could have accepted all the answers so far to the question, as each one provides a valid solution.
0

This will return text like var='value';

awk '
    match($1, /^\$([[:alnum:]_]+)=?/, m){
        gsub(/^[^=]+=[[:space:]]*/, "")
        print m[1] "=" $0
    }
' < file.php

You can eval the output.

update

This is a lot simpler than the above. I realized all you need to do is delete the first $ and remove the spaces around the =:

sed -e 's/\$//' -e 's/ *= */=/' file.php
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5 Comments

Wow! That's a neat way of doing it. It will fail on a line which makes a call to a mysql_connect function $db=mysql_connect(..., but I can easy shift that to a different include to get round that.
...and by fail, I mean the eval part will fail.
The sed version doesn't work quite as well, as it doesn't cope with the other lines in the file. These include <?php, ?> and comment lines, ini_set, require_once and a few other PHP specific lines.
Accepted on the basis of the awk part of the answer, as it deals with all the variables in my config.php.inc, without me having to hard code each variable.
@Bryan, I was going on your code sample that only showed variable declarations. Glad the awk version worked for you though.
0

It sound like that there is a missing \

Check if this is not \\$dbuser

If you have access to perl try:

dbuser=$(perl -ne "print \$1 if /\$dbuser.*'(.*)'/" config.php.inc)

Note : -e use next parameter as a one liner script
-n use all parameter as file argument
print $1 print the matched pattern when matched
The parathesis in the regex define the $1 capture group.

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1 Comment

Adding the second escape character fixed the problem. I don't have perl available to me at the moment, but might give that a try. Do the parenthesis define that part that is output from match?
0

With some basic checking and safety

eval $(sed -n "s/^\$\([a-zA-Z][a-zA-Z0-9_]*\) *= *'\(.*\)' *;/\1='\2';/p")
echo User:$dbuser Pass:$dppass Host:$dhhost

will print for your example

User:fred Pass:abc123 Host:127.0.0.1
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