Shell heredoc inside php heredoc - php

Question

I have something similar to this in a php script:
<?php
...
function log() {
// saving the log into a file.
exec(<<<BASH
cat >> $logFile <<EOF
$log
EOF
BASH
);
}
...
As you can see the two heredocs (BASH is php and EOF is shell) end as one would think is correct, but when I read the log created the log has something like this:
...
my logged string of an important event
EOF
my logged string of another important event
EOF
...
And I check the apache log and it has the following entries:
sh: line 1: warning: here-document at line 0 delimited by end-of-file (wanted `EOF')
What am I doing wrong?
Please, I am aware that there are many other implementations, such as using php functions or using quotes instead of heredocs. But I am curious about why in this particular case this does not work.
EDIT.
I clarified the code so it is more clear that I am talking about php running shell commands.

Answer 1

Updated answer for PHP case
Suppose we have test.php file with the following contents:
<?php
function mylog() {
$logFile = 'test.log';
$log = 'test';
exec(<<<BASH
cat >> $logFile <<EOF
$log
EOF
BASH
);
}
mylog();
Then php test.php produces the right thing(!):
rm -f test.log
php test.php
cat test.log
Output:
test
Now let's indent the Bash part:
<?php
function mylog() {
$logFile = 'test.log';
$log = 'test';
exec(<<<BASH
cat >> $logFile <<EOF
$log
EOF
BASH
);
}
mylog();
Now php test.php produces exactly what you've written about in your
question:
rm -f test.log
php test.php
cat test.log
Output:
sh: line 2: warning: here-document at line 0 delimited by end-of-file (wanted `EOF')
test
EOF
Apparently, you have your Bash part indented, which is an invalid Bash syntax. So you just need to remove indentation for the Bash part. At least, EOF shouldn't be indented.
Original answer where I thought the OP meant pure Bash
exec executes a command, but you need to evaluate bash expression. So you need eval instead.
To construct the command using eval use the following:
eval "$(
cat <<'EOF'
cat >> test.log <<EOF2
log contents
EOF2
EOF
)"
So we constructed a Bash variable with "$( and )". Within the variable we created a here-doc string with cat <<'EOF' and EOF, where single quotes disable parameter substitution so we can enter literal text.(no evaluation). Then we've written log contents by means of another here-doc string created with <<EOF2 and EOF2.
We might save save the Bash variable, then use it as many times as we like:
cmd="$(
cat <<'EOF'
cat >> test.log <<EOF2
log contents
EOF2
EOF
)"
rm test.log
eval "$cmd"; eval "$cmd"; eval "$cmd"
cat test.log
Output:
log contents
log contents
log contents
See docs for here documents.