Using bash variable substitution instead of cut/awk

Question

Can I use bash variable substitution to extract a piece of a variable based on a delimeter? I'm trying to get the immediate directory name of a filename (in this case, foo).

$ filename=./foo/bar/baz.xml

I know I could do something like

echo $filename | cut -d '/' -f 2

or

echo $filename | awk -F '/' '{print $2}'

but it's getting slow to fork awk/cut for multiple filenames.

I did a little profiling of the various solutions, using my real files:

echo | cut:

real    2m56.805s
user    0m37.009s
sys     1m26.067s

echo | awk:

real    2m56.282s
user    0m38.157s
sys     1m31.016s

@steeldriver's variable substitution/shell parameter expansion:

real    0m0.660s
user    0m0.421s
sys     0m0.235s

@jai_s's IFS-wrangling:

real    1m26.243s
user    0m13.751s
sys     0m28.969s

Both suggestions were a huge improvement over my existing ideas, but the variable substitution is fastest because it doesn't require forking any new processes.

Answer 1

You can remove the shortest leading substring that matches */

tmp="${filename#*/}"

and then remove the longest trailing substring that matches /*

echo "${tmp%%/*}"

Answer 2

    echo $f
    a/b/c

    $ (IFS='/';set $f; echo $1)
     a

    $ (IFS='/';set $f; echo $2)
     b

    $ (IFS='/';set $f; echo $3)
     c

with wild card it seems to work with double or single quotes -

    f="a?b?c"
     $(IFS="?"; set $f; echo $1)
     a
    echo $f
    a*b*c
    (IFS="*"; set $f; echo $1)
    a

yes, you'll have to unset the IFS back to default

    unset IFS

Answer 3

Feed the list to awk to speed it up:

awk -F '/' '{print $2}' < <(find /usr)
awk -F '/' '{print $2}' < inputfile

Demonstration:

time awk -F '/' '{print $2; SUM++} END {print "number of directories found: " SUM}' < <(find /usr -type d)
usr
usr
.
.
number of directories found: 16748

real    0m8.910s
user    0m0.050s
sys     0m0.050s

Answer 4

Why don't you use the "dirname" command, instead of all this awk/sed/cut stuff?

filename=./foo/bar/baz.xml
dirname $filename

Yields:

./foo/bar