How to fasten nested "for" loops

[allanm77]

Hey All,

I have a script/command which has a for loop nested inside of another for loop -

for i in `cat file1`; do echo "$i******"; for j in `cat file2`; do command $i arg1  |grep $j; done; done

file1

APP1

APP2

..

file2

library1

library2

..

command = libinfo APP1

output of the command list all libraries for APP1, but I want to grep for only the ones given in file2.

How can fasten this up?

Thanks,

Allan.

[James R. Ferguson]

---

@allanm77 wrote:

I have a script/command which has a for loop nested inside of another for loop -

for i in `cat file1`; do echo "$i******"; for j in `cat file2`; do command $i arg1  |grep $j; done; done

...

output of the command list all libraries for APP1, but I want to grep for only the ones given in file2.

How can fasten this up?

---

I suppose by "fasten this up" you mean "make faster".

That said, you could use :

#!/usr/bin/sh
while read i
do 
     echo "$i******"
     command $i arg1 | grep -f file2
done < file1

Look at the manpages for 'grep'.  With '-f pattern_file' the regular expression (grep and grep -E) or strings list (grep -F) is taken from the pattern_file.

Regards!

...JRF...

[Dennis Handly · Accepted solution]

>I suppose by "fasten this up" you mean "make faster".

Or "speed up".  :-)

>With '-f pattern_file'

Right, using vector methods.

Also, you don't have to use while, for loops also take infinite args but they all have to be read into memory:

for i in $(< file1); do

   echo "$i******"

   command $i arg1 | grep -f file2

done

If command takes a list of arguments, you may be able to invoke command once as in nm(1):

nm -pxAN $(< file1) | fgrep -f file2

[allanm77]

Thanks Dennis!

[James R. Ferguson]

Hi (again) :

And what was wrong with the substance of the answer I provided --- the use of 'grep -f' ?

Both of us, too, eliminated your useless 'cat'.   Did you notice that either?

...JRF...

[allanm77]

Totally missed, thanks!