Why do commented lines in a linux configuration file sometimes work? [duplicate]
Solution 1:
Any line that begins with a #
is a comment in many languages and is ignored by the interpreter (perl
etc.).
However, if the first line of a script in Linux begins with a #!
(shebang as it is called), it is not a comment but a directive to the program loader to actually run the program specified after #!
and pass it the name of your file as the last argument.
For example, if the first line is
#!/usr/bin/perl -w
it means the shell will actually invoke /usr/bin/perl -w /path/to/the/script
and you don't need to specify a program to run this script, you can run it using
/path/to/the/script
if you have the permission to run it and it is located on a filesystem supported for execution and the file has the permission to be executed.
For the interpreter, however, this line is always just a comment, so if the script is executed as:
perl /path/to/the/script
then the line has no effect. (Thanks to Ruslan for pointing this out).
Be warned that #
is not always indicative of a comment. For example, a statement beginning with a #
in C is pre-processor directive and not a comment.
In your case, the line is a comment and will be ignored while execution.
Update:
The file you are talking about is a menu.lst
for which a comment is a line beginning with ##
and not #
. (Source)
Solution 2:
The line beginning with #!
is still a comment, in that it is not executed as normal commands.
But not only is it a valid comment but it's also a hashbang, a line that can be used to indicate the interpreter to be used to execute these commands if the script is called on its own.
Hashbangs begin with a #
in order to be backward-compatible with interpreters that don't read hashbangs, in which case they will simply be interpreted as comments and ignored.