I have a string like this

TEST="/dev/sda1 on /media/sda1 type vfat (rw,relatime,fmask=0000,dmask=0000,allow_utime=0022,codepage=cp437,iocharset=iso8859-1,quiet)"

(Result from mount | grep sda1)

where I want to match the mount point. My regex (adopted from here) is

(?<=on[ \t])(.*)(?=[ \t]type)

But for some reasons it doesn't work for me with several tools (Busybox ash 1.14.2):

echo $TEST | grep -o -e '(?<=on[ \t])(.*)(?=[ \t]type)'

Gives me no result.

echo $TEST | awk 'match($0, /(?<=on )(.*)(?= type)/){print $0}'

Returns an error awk: bad regex '(?<=on[ ])(.*)(?=[ ]type)': Invalid preceding regular expression

expr match "$TEST" '\(?<=on[ \t]\)\(.*\)\(?=[ \t]type\)'

Also returns an empty result.

I feel kinda stupid.

  • Why don't you just try to match on (.*) type?
    – lgeorget
    Apr 22, 2014 at 13:25
  • Note also that if you want the third field of a line, awk can give it to you for free: echo $TEST | awk '{print $3}'.
    – lgeorget
    Apr 22, 2014 at 13:29
  • AFAIK blank is also a valid character for an USB device so this would break this code. Otherwise I could use echo $TEST | cut -d' ' -f3
    – Noir
    Apr 22, 2014 at 13:34

1 Answer 1


Lookarounds are perl regex features. GNU grep implements them (with the -P option). I cannot say whether any busybox command does.

In this case though, you're just looking for the work after "on". Choose one of

echo "$TEST" | awk '{for (i=1; i<=NF; i++) if ($i == "on") {print $(i+1); break}}'
echo "$TEST" | sed 's/.*on[[:blank:]]\(.*\)[[:blank:]]type.*/\1/'

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