[SOLVED] bash: So simple yet so impossible to find (elsewhere).

L_Carver · 09-13-2018, 01:00 PM

I seem to be forgetting little things about bash scripting. Such as: what is the # to ignore a command in a script called (cancel or nullify are the only things that comes to mind.)
As in this example:

Code:

#if [  "$(ls *.bak 2>/dev/null)"]; then

Carver

astrogeek · 09-13-2018, 01:04 PM

That is called "commenting" - it is not so much about cancelling a command, although that is a frequent and useful way to use it! It provides a way for you to add comments to your code - everything after the # is ignored by the language interpreter.

It is easy to find in man bash

Code:

COMMENTS
       In  a  non-interactive  shell,  or  an interactive shell in which the interactive_comments option to the
       shopt builtin is enabled (see SHELL BUILTIN COMMANDS below), a word beginning with #  causes  that  word
       and  all  remaining  characters  on  that line to be ignored.  An interactive shell without the interac-
       tive_comments option enabled does not allow comments.  The interactive_comments option is on by  default
       in interactive shells.

pan64 · 09-13-2018, 01:26 PM

just remember, the comment sign is only valid for one line, nothing more. So if you comment an if (like in your own example) you need to comment all the lines below to the closing fi. Otherwise you will (may) get syntax errors.
(Almost) all the programming languages has commenting features, it is not really bash specific thing.
For example in shells you can use #, in C++ there are 2 kind of comments available (// for single line, /* ... */ for multi-line comments), also you can have comments in sql (using --), perl (#), python (#), java (like C++) and so on

L_Carver · 09-22-2018, 07:03 AM

Quote:

Originally Posted by pan64

just remember, the comment sign is only valid for one line, nothing more. So if you comment an if (like in your own example) you need to comment all the lines below to the closing fi. Otherwise you will (may) get syntax errors.
(Almost) all the programming languages has commenting features, it is not really bash specific thing.
For example in shells you can use #, in C++ there are 2 kind of comments available (// for single line, /* ... */ for multi-line comments), also you can have comments in sql (using --), perl (#), python (#), java (like C++) and so on

Yes, I remembered that much. It was just what that was called that I'd forgotten.

Carver

hydrurga · 09-22-2018, 07:32 AM

Quote:

Originally Posted by L_Carver

Yes, I remembered that much. It was just what that was called that I'd forgotten.

Carver

That symbol is actually multi-named.

Knock yourself out: https://en.wikipedia.org/wiki/Number_sign

We in the UK at least normally call it a "hash".