Sed 从文件中删除日志错误实例，但前提是文件不存在？

Question

Please note: this is purely a bash scripting and sed question, even though it mentions a few other technologies (MySQL, Docker, etc.) in passing, for context.

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Looking at a bash script that runs when the official MySQL 8.0 Dockerfile builds, I see this:

if [ -n "$MYSQL_LOG_CONSOLE" ] || [ -n "console" ]; then
  # Don't touch bind-mounted config files
  if ! cat /proc/1/mounts | grep "etc/my.cnf"; then
    sed -i 's/^log-error=/#&/' /etc/my.cnf
  fi
fi

...and I'm trying to make sense of what it does. A few things don't make sense to me, but this is from the official MySQL Docker project, so obviously they know what they're doing. It looks like its saying:

1. check to see if a string variable called MYSQL_LOG_CONSOLE is not null, or if the hard-coded string literal "console" is not null
2. If either are true, and then search available mount info ( proc/1/mounts ) to see if etc/my.cnf is referenced in it
3. If etc/my.cnf is not contained inside of proc/1/mounts , then remove all instances of log-error from inside etc/my.cnf

To start with, what's the point of checking whether the string literal "console" is null or not with [ -n "console" ] ? How could a non-null string literal ever be...null?

But the main question I have though is with the sed :

sed -i 's/^log-error=/#&/' /etc/my.cnf

Am I interpreting this sed command correctly? Remove all instance of log-error from the file...if the file doesn't exist?, I'm clearly missing something. just not sure what. Thanks in advance!

Answer 1

what's the point of checking whether the string literal "console" is null or not with [ -n "console" ]?

The file is generated from the template :

 if [ -n "$MYSQL_LOG_CONSOLE" ] || [ -n "%%DEFAULT_LOG%%" ]; then

Logging to console is by default enabled only in mysql 8, from generating script :

 declare -A DEFAULT_LOG DEFAULT_LOG["5.6"]="" DEFAULT_LOG["5.7"]="" DEFAULT_LOG["8.0"]="console"

How could a non-null string literal ever be...null?

It cannot be.

Am I interpreting this sed command correctly?

No. The sed command doesn't remove the lines, it prepends # in front of the lines starting with log-error= .

Remove all instance of log-error from the file...

No.

if the file doesn't exist?!

No, only if the file is not mounted.