command line crontab editing

[linmac]

hi all,

i got crontab file like this:

50 1 * * * * /usr/local/bin/script1
50 2 * * * * /usr/local/bin/script2
50 3 * * * * /usr/local/bin/script3
..
..
.. and more.

question:-

1) how from shell script file, i add # to line 1 and line3 in first run?

2) remove # from line 1 and line 3

what i want is one script that check if line 1 and line 3 have comment (#). if got, the script remove the # and if no add the comment. 2 function in one script. can anybody help me on this? thanx in advance.
(maybe using sed or awk, either one)

 

[CaKiwi]

Here's an awk script to do it

{
if (NR==1 || NR==3) {
if (!sub(/^#/,"&quot) $0 = "#" $0
}
print
}

CaKiwi

 

[iribach]

cp file xxfile
#1.loop (insert #):
sed -e '1s/.*/#&/;3s/.*/#&/' xxfile >file
#2.loop (remove #):
sed -e '1s/#*\(.*\)/\1/;3s/#*\(.*\)/\1/' xxfile >file
# check if worked
[ -s file ] && rm xxfile || mv xxfile file

#PS: if you modify crontabs using scripts
#do it properly, checking owner and perms