Bash how to edit a variable

Question

I am new to using bash. Now I am about to read a value, but the output of the console is too long and I just want to shorten it to the specific value.

netstat -m

24270/3315/27585 mbufs in use (current/cache/total)
4142/1724/5866/1000000 mbuf clusters in use (current/cache/total/max)
40/1478 mbuf+clusters out of packet secondary zone in use (current/cache)
0/145/145/524288 4k (page size) jumbo clusters in use (current/cache/total/max)
0/0/0/524288 9k jumbo clusters in use (current/cache/total/max)
0/0/0/83968 16k jumbo clusters in use (current/cache/total/max)
...

Now I want to get to the 5866 in the second line and wrap it in a variable. Currently my script looks like this:

mbuf_stat=$(netstat -m)
mbuf=$mbuf_stat
mbuf=${mbuf#*)}
mbuf=${mbuf#*/}
mbuf=${mbuf#*/}
mbuf=${mbuf%%/*}
echo "$mbuf"

Is there an easier way to do this? It seems pretty complicated to me. Unfortunately, I have not found a simpler way yet.

You could use bash regular expressions to do this kind of parsing, but remember that the primary purpose of bash is to run other programs to do your actual data processing, not do the processing itself. — chepner
– chepner, Commented Jul 11, 2022 at 15:08
The answers given below are right. But also note that in many cases, the tool (netstat in this case) may have some command-line option to provide the output in more parsable/precise manner. My comment may not be relevant in the case of netstat, but I am just putting it out here as a note since you are new to shell scripting. :-) — anishsane
– anishsane, Commented Jul 11, 2022 at 15:17

Barmar · Accepted Answer · 2022-07-11 15:05:20Z

2

Use awk for this:

mbuf=$(netstat -m | awk -F'/' 'NR == 2 { print $3; exit }')

-F'/' makes / the field separator. NR == 2 matches the second line of the file. print $3 prints the third field, which contains 5866, then exit exits the script.

answered Jul 11, 2022 at 15:05

Barmar

788k57 gold badges554 silver badges668 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Dominique · Accepted Answer · 2022-07-11 15:08:04Z

1

What about this:

mbuf=$(netstat -m | grep "mbuf clusters in use" | awk -F/ '{print $3}')

The difference with the answer from Barmar is that I'm looking for the line, containing "mbuf clusters in use" instead of assuming it's the second one.

answered Jul 11, 2022 at 15:08

Dominique

17.6k20 gold badges80 silver badges161 bronze badges

2 Comments

jordanm Over a year ago

Unnecessary grep: mbuf=$(netstat -m | awk -F/ '/mbuf clusters in use/ {print $3}')

Dominique Over a year ago

@jordanm: I have the habit of filtering using grep and adapting the output using awk :-)

ufopilot · Accepted Answer · 2022-07-11 15:12:33Z

1

$ netstat -m | awk -F/ '/mbuf clusters in use/{print $3}' 
5866

answered Jul 11, 2022 at 15:12

ufopilot

3,9752 gold badges13 silver badges14 bronze badges

Comments

RARE Kpop Manifesto · Accepted Answer · 2022-07-11 17:18:29Z

0

mbuf=$( netstat -m | 
        
gawk '$_=$--NF' RS='^$' FS='/[^/]+mbuf[^/]*clusters in use.*$|[/\n]+|$' )

or

mawk -F/ '$!NF=$((NF*=/mbuf[^/]*clusters in use/)^_+NR)'

edited Jul 11, 2022 at 17:18

answered Jul 11, 2022 at 17:10

RARE Kpop Manifesto

3,0015 silver badges15 bronze badges

Collectives™ on Stack Overflow

Bash how to edit a variable

4 Answers 4

Comments

2 Comments

Comments

Comments

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

2 Comments

Comments

Comments

Related