Comandline arguements when perl code is getting executed from command line

[jesuashok]

fellow monks,

#!/usr/bin/ksh

cat file | while read i
do
 file_name=`echo $i | awk -F"|" '{print $1}'` #get the file_name
 export type=`echo $i | awk -F"|" '{print $2}'` #get the customer type
+ setting for the file
 perl -nle '/TABLE/ && print "$ARGV:$_:$ENV{type}"' $file_name
done

In the above shell script, I am getting the filename and type of file, this both has to be printed when a particular pattern matches in the filename.
Through $ARGV I can get the filename and get printed. How can I print the `type` without using `export type` and $ENV{type} in print statement ?

[merlyn]

First, you have a useless use of cat.

Second, why are you doing shell at all? Why not do this all in Perl?

open my $f, "<", "file" or die;
while (<$f>) {
  chomp;
  my ($file_name, $type) = split /\|/;
  open my $inner, "<", $file_name or die;
  while (<$inner>) {
    if (/TABLE/) {
      print "$file_name:$type\n"; # last ?
    }
  }
}

[jesuashok]

hi merlyn,

thanks for giving me( all monks too ) a nice note on "useless use of cat". My shell script does lot of other task also. I have just copied a required part and asked in perlmonks. Just I am curious to know how that can be done ? that is all. Doing everything in perl is not a bad idea at all.

thanks a lot merlyn.

[ikegami]

Pass it as a parameter, and it'll be in @ARGV.

[ysth]

Not a good idea when using the -n switch. Unless you mean a BEGIN { } block and maybe Getopt::*?

[ikegami]

He could use BEGIN { $type = shift(@ARGV); }, he could use -s or he could get rid of -n.

[jesuashok]

#!/usr/bin/ksh

cat file | while read i
do
 file_name=`echo $i | awk -F"|" '{print $1}'` #get the file_name
 export type=`echo $i | awk -F"|" '{print $2}'` #get the customer type
+ setting for the file
 perl -nle '/TABLE/ && print "$ARGV:$_:@ARGV"' $file_name $type
done

thanks a lot, the above too worked fine as expected.

[sgt]

hi, don't you have a shell that supports $(...) to avoid backquotes `...`; the first does nest properly and the second does not. Modern shell hackers consider the second form obsolete, but yes it is portable and is probably the way to go if you do configure-like sport...

cheers --stephan

[ikegami]

Not really. -n tries to open the value of $type as a file.

By the way, won't you have a problem if $file_name or $type contains shell metacharacters?

[Thelonius]

This should work:

perl -slne '/TABLE/ && print "$ARGV:$_:$type"' -- -type=$type $file_na
+me

See the -s swith in the perlrun manpage.

[jdporter]

ksh is a pretty decent scripting language, actually.

#!/usr/bin/ksh

while read i
do
    file_name=${i%\|*}
    cust_type=${i##*\|}
    if ! [[ -z "$file_name" || -z "$cust_type" ]]
    then
        while read j
        do
            if [[ "$j" = *TABLE* ]]
            then
                print "$file_name:$j:$cust_type"
            fi
        done < $file_name
    fi
done < file

[sgt]

I do agree ;) the latest version ksh93s has just been released and offers quite a lot of new goodies (regex extensions and lots of utf8 fixes). The extension mechanism that has been there since the beginnings of ksh93 in 93 ;) is quite. By the way as cat is a builtin of modern ksh (and the last command of the pipeline in ksh is executed by main()) the efficiency of 'cat...| cmd' is (usually) hardly a problem. From the command line, and I often use a cat like this, in case I need to edit later to put 'cat -evnt' o even to sandwich some extra "line" like this

 { echo; cat ...; echo; } | whatever

But... there is an exception actually 'cmd | while read' is probably one of "worst" constructs in terms of efficiency as the shell needs to read one byte at a time in case another command in the body of the while could compete for stdin. If it is *not* the case, a trick like this (for modern enough shells) is nice:

use 'cmd | while read -u9 ...; done 9<&0-'
desc 0 is duped on desc 9 and then closed

# an example of healthy competition for stdin
while read header
do
     dd ...
done

Note that you need a true move-close and not 9>&0 0<&- as by the time the dup is done, the close doesn't know about it and does not set a share flag. ksh88 does not have the logic needed for example. If your system pipes are dumb (no peek ahead) the trick does not work either.

I finish with some hack. the 'while < file' idiom does that move-close magic under the hood (and does a 'set' on each line read) and is quite efficient. "under cover select" is what you get if you stack them 'while <file1 <file2 ...' ;)

% stephan@labaule (/home/stephan) %
% $0 --version; cat -n hi1                  
  version         sh (AT&T Labs Research) 1993-12-28 r
     1  just
     2  another
     3  ksh
     4  hacker

% stephan@labaule (/home/stephan) %
% while < hi1; do print -n $1' '; done; echo
just another ksh hacker

David Korn's own words on this (thread of ast-users mailing list on july 2006) are interesting from a un*x perspective: https://mailman.research.att.com/pipermail/ast-users/2006q3/001084.html

enjoy --stephan