awk action when matching one field and not matching another

[Mudgen]

I need to script some /etc/fstab option changes for security standard compliance and am having a problem with matching one field (mount point) and excluding a no-match on another (i.e. options already contain the one I'm adding). I can't seem to make the no-match work in conjunction with the match.

The following adds my option whether or not it's already present. I've tried both the ~ && and the !~ || variations (and a bunch of others).

This code keeps adding "nodev" when it's already there. What am I not getting?

#!/bin/bash
## Open /etc/fstab as input to command line, replace it within braces with modified copy
FSOPT="nodev"
FSOPTCOMMA="$FSOPT,"
FSYS="^/tmp$"
#syntax ok, does not exclude $4!~/FSOPT/
( rm /etc/fstab && awk -v FSYS=$FSYS -v FSOPT=$FSOPT -v FSOPTCOMMA=$FSOPTCOMMA ' $4 !~ /FSOPT/ && $2~FSYS{$4=FSOPTCOMMA$4}1' OFS="\t"  > /etc/fstab ) < /etc/fstab

It does fine when /tmp does not already have nodev, but on second run results in:

/dev/VolGroup00/LogVol02        /tmp    ext3    nodev,nodev,defaults    1       2

[Mudgen]

The tl;dr version:

This awk code outputs all fstab lines, prepending "nodev" to $4 if $2 matches "^/tmp$". I want to add "nodev" only if it is not already in $4. How do I do that?

awk -v FSYS="^/tmp$" -v FSOPT="nodev" -v FSOPTCOMMA="nodev," ' $2~FSYS{$4=FSOPTCOMMA$4}1' OFS="\t"   < /etc/fstab

[watael]

hi,

variable expansion does not occur between / and /
see

$ awk -v var="bar" '$1 !~ /var/{ print}' <<<"foo
bar
baz"
foo
bar
baz
$ awk -v var="bar" '$1 !~ var{ print}' <<<"foo
bar
baz"
foo
baz
$

[Mudgen]

hi,

variable expansion does not occur between / and /
see

$ awk -v var="bar" '$1 !~ /var/{ print}' <<<"foo
bar
baz"
foo
bar
baz
$ awk -v var="bar" '$1 !~ var{ print}' <<<"foo
bar
baz"
foo
baz
$

Thank you, Watael. That's generally useful to know, but can you help me understand how to apply it to my quoted code and need to add a second test? Or a workaround?

[watael]

is that so difficult?
look at another example:

$ awk -v var1="o" -v var2="a" '$2 ~ var1 && $1 !~ var2{ print}' <<<"foo bar
bar baz
baz foo
foo foo"
foo foo

[Mudgen]

Ah. Took me a moment to get it. I thought there was something wrong with the way I was performing the tests in the chain. It was the pattern matching.

awk -v FSYS=$FSYS -v FSOPT=$FSOPT -v FSOPTCOMMA=$FSOPTCOMMA ' $4 !~ FSOPT && $2~FSYS{$4=FSOPTCOMMA$4}1' OFS="\t"   < /etc/fstab

This does what I want (with the shell variables previously set).