Using sed inside system call in awk

Shell Programming and Scripting
1

HI ,
I am trying to write a code where if a file system has / at the end then replace it with null but it should not affect root file system /

for example if
ip is /var/opt/home/ then o/p is /var/opt/home
but if ip is / then it should remain /.

for this i am using below code but no success

echo "hi/" |awk -F "/" -v line=$0 '{ if ($NF == "" && NF -eq 2 && $1 == "") print $0;else print system("echo " $line \"| (sed 's>/$>>')\");}'

I am getting error:

I have tried numerous combinations but no luck.

thanks for help

Jcpratap

2

That method is quite an overkill by the looks of it. You could simply do something like this (providing you have an bash/ksh that supports this form of parameter expansion):

fs="/one/two/three/"
tmp=${fs%/}
echo ${tmp:-/} # The expected result

I imagine there are even smarter ways to.

3

Hello Jcpratap,

It seems a very heavy way to achieve this. Could you do something based on the following instead?

my_dir="hi/"
my_dir="${my_dir%/:=/}"
echo $my_dir

By way of explanation, the variable is substituted for a value based on itself. It could be done in two steps for more clarity like this:-

my_dir="hi/"
my_dir="${my_dir%/}"        # 1st substitution
my_dir="${my_dir:=/}"       # 2nd substitution
echo $my_dir

The first substitution trims off a trailing / from whatever the input string is.
The second substitution assigns the value / if the input is null, i.e. it used to be just / before it was trimmed to nothing. The first code suggestion just merges these two together.

I hope that this helps,
Robin

4

Another approach:-

awk '/[^/]+/{sub(/\/$/,X)}1'
5

You are spawning another process with that though and not very easy to understand if you are not a awk Jedi Master like yourself.

6

@rbatte1: in my bash , my_dir="${my_dir%/:=/}" doesn't work. Is that a "bashism" or do I do sth. wrong?

7

thanks

awk '/[^/]+/{sub(/\/$/,X)}1'

works

can you explain the same

8

Hi Yoda, the / character needs to be escaped within an awk regex constant expression that is terminated by two slashes, even within a bracket expression:

awk '/[^\/]/{sub("/$",x)}1'

awk: Regular Expressions

---
Other options:

sed 's|\(.\)/$|\1|'

perl -pe 's/(?<=.)\/$//'
9

/[^/]+/ - if record has one or more occurrence of any character other than / (to exclude root fs)

sub(/\/$/,X) - substitute or replace / in the end with X which is null or undefined variable.

1 - a non zero value or true, forces awk to print record.