A strange sign

Gins · 07-26-2006, 04:56 AM

#!/bin/bash

array=(red green blue yellow magenta)

len=${#array[*]}

echo "The array has $len members. They are:"

i=0
while [ $i -lt $len ]; do
echo "$i: ${array[$i]}"
let i++
done

-----------------------------------------------

Usually this sign [#] is for comments. If you look at the above, you will read this ---> len=${#array[*]} .

What is the use of it here? I would like to read your comments.

prozac · 07-26-2006, 05:12 AM

This is what the bash manual says:

Quote:

A command may not follow a comment on the same line. There is no method of terminating the comment, in order for "live code" to begin on the same line. Use a new line for the next command.

but after executing the script, i got the following:

Quote:

The array has 5 members. They are:
0: red
1: green
2: blue
3: yellow
4: magenta

prozac · 07-26-2006, 05:17 AM

Of course, an escaped # in an echo statement does not begin a comment. Likewise, a # appears in certain parameter substitution constructs and in numerical constant expressions.

Quote:

echo "The # here does not begin a comment."
echo 'The # here does not begin a comment.'
echo The \# here does not begin a comment.
echo The # here begins a comment.

echo ${PATH#*:} # Parameter substitution, not a comment.
echo $(( 2#101011 )) # Base conversion, not a comment.

The standard quoting and escape characters (" ' \) escape the #.

Certain pattern matching operations also use the #.

Gins · 07-26-2006, 05:49 AM

Thanks Prozac for the reply.

So it is doing some conversion here.

I can't fathom out the conversion here.

Hko · 07-26-2006, 08:28 AM

Quoting bash's man page:

Code:

${#parameter}
       The length in characters of the value of  parameter  is  substi-
       tuted.   If  parameter  is  * or @, the value substituted is the
       number of positional parameters.  If parameter is an array  name
       subscripted  by  *  or @, the value substituted is the number of
       elements in the array.

jim mcnamara · 07-26-2006, 08:51 AM

The ${#var} syntax is derived from Korn Shell. As Hko reports above it is for getting lengths or number of elements.