How to execute the rest of the code after commenting multiple lines? - Shell Programming and Scripting

Yamini Thoppen · #1 01-01-2008

Hi,

As I have seen in this forum how to comment multiple lines in the script, but it does not work properly for me.
It is blocking the code but it does not execute the rest of the codes.

This is my code

#! /usr/bin/ksh
month='date +"m%"'

: << Comments Block
if [ "$month -eq 3 ] || [ "$month -eq 6 ]
then
echo "inc = 1"
else
echo "inc = 2"
fi
-- End Comments Block

case $month in
3|6|9|12) echo "Yes";;
*) echo "No";;
esac
echo "This is the last line"

My query is after the comments block, it does not execute the case statement. Can you pls explain it?

fpmurphy · #2 01-01-2008

I strongly urge you to use the traditional # method of commenting out shell
script code.

That being said, the problem with your block comment trick is your invalid
syntax for here documents.

Code:

: <<COMMENTBLOCK
if [ "$month -eq 3 ] || [ "$month -eq 6 ]
then
echo "inc = 1"
else
echo "inc = 2"
fi
COMMENTBLOCK

Yamini Thoppen · #3 01-01-2008

Quote:

Originally Posted by fpmurphy

I strongly urge you to use the traditional # method of commenting out shell
script code.

That being said, the problem with your block comment trick is your invalid
syntax for here documents.

Code:

: <<COMMENTBLOCK
if [ "$month -eq 3 ] || [ "$month -eq 6 ]
then
echo "inc = 1"
else
echo "inc = 2"
fi
COMMENTBLOCK

Hi Murphy,
Thanks for your reply.

After trying with your sample code, it does not work for me. I dont know what might be the problem.

rubin · #4 01-01-2008

It looks like there is some confusion here.
What fpmurphy is trying to say is that you need to comment out the lines (if needed) that don't need to be executed using # sign, like this:

Code:

#  :<<COMMENTBLOCK
# if [ "$month -eq 3 ] || [ "$month -eq 6 ]
# then
# echo "inc = 1"
# else
# echo "inc = 2"
# fi
# COMMENTBLOCK

In case you are trying to use a HERE document, as suggested you need to get rid of the colon : in front of the sign <<, and no space at the final COMMENTBLOCK :

Quote:

<<COMMENTBLOCK
if [ "$month -eq 3 ] || [ "$month -eq 6 ]
then
echo "inc = 1"
else
echo "inc = 2"
fi
COMMENTBLOCK

So if you need those lines commented out you need to use the first code.

If you are trying to achieve something else with your script, then you need to look in your script and change it accordingly, or post here what are you trying to achieve.

porter · #5 01-01-2008

Quote:

if [ "$month -eq 3 ] || [ "$month -eq 6 ]

Your quotes are open.

drl · #6 01-01-2008

Hi.

A few comments. First, there is a "quoted" string feature in the shells for HERE documents. The use prevents evaluation of everything up to the closing string, including unclosed quotes, variable issues, etc.

Second, ksh does a good job of diagnosing a missing, closing, matching HERE document string -- bash (2 & 3) simply stop.

A ksh example:

Code:

#!/usr/bin/env ksh

# @(#) s1       Demonstrate quick method to render code block inoperable.

set -o nounset
echo

debug=":"
debug="echo"

## The shebang using "env" line is designed for portability and
#  demonstrations. For higher security, use:
#
#  #!/bin/ksh -

## Use local command version for the commands in this demonstration.

echo "(Versions displayed with local utility \"version\")"
version >/dev/null 2>&1 && version ksh

echo
echo " Commands before commented-out block."

: <<'EOF'
garbage
junk
worthless
utterly without merit
" crud inside of double quotes "
' debris inside single quote '
" mess inside unmatched double-quotes
' detritus inside an unmatched single-quote pair
...
and so on.
EOF

echo
echo " Commands after  commented-out block."

echo
echo " Failed block quote due to unmatched HERE stings:"

echo
echo " Commands before commented-out block."

: <<'MISSING'
more junk
OOPS!

echo " Commands after  commented-out block."

exit 0

producing:

Code:

% ./s1

(Versions displayed with local utility "version")
pdksh 5.2.14 99/07/13.2

 Commands before commented-out block.

 Commands after  commented-out block.

 Failed block quote due to unmatched HERE stings:

 Commands before commented-out block.
./s1[53]: here document `MISSING' unclosed

I don't use ksh for reasons of availability (my shebangs almost always use simple "sh"), but in this case ksh is superior ... cheers, drl

Yamini Thoppen · #7 01-01-2008

Quote:

Originally Posted by rubin

It looks like there is some confusion here.
What fpmurphy is trying to say is that you need to comment out the lines (if needed) that don't need to be executed using # sign, like this:

Code:

#  :<<COMMENTBLOCK
# if [ "$month -eq 3 ] || [ "$month -eq 6 ]
# then
# echo "inc = 1"
# else
# echo "inc = 2"
# fi
# COMMENTBLOCK

In case you are trying to use a HERE document, as suggested you need to get rid of the colon : in front of the sign <<, and no space at the final COMMENTBLOCK :

So if you need those lines commented out you need to use the first code.

If you are trying to achieve something else with your script, then you need to look in your script and change it accordingly, or post here what are you trying to achieve.

Hi Rubin,

Thanks for your explanation. I will write exactly what I need

Like in C or in C++, we have multiple lines of comments start like

/*
bla bla bla
*/

Likewise, I need the same kind of comments in Shell scripts. Is it possible here ?

1 #! /usr/bin/ksh
2 month=`date +"%m"`
3 echo $month
4
5 <<COMMENTBLOCk
6 if [ "$month" -eq 3] || [ "$month" -eq 6]
7 then
8 echo "inc = 1"
9 else
10 echo " inc = 2"
11 fi
12 COMMENTBLOCK
13
14 case $month in
15 3|6|9|12) echo "Yes";;
16 *) echo "No";;
17 esac
18
19 echo "This is the last line"

Query : I need to block the line number from 5 to 12 (except # option and line no from 14 to 19 should execute as usual. Can you pls give the solution for it?

Many of Unix Experts are replied for my query. Many thanks to you.

Thanks
Yamini

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