Need shell script to read two file at same time and print out in single file Post: 302295455

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Top Forums Shell Programming and Scripting Need shell script to read two file at same time and print out in single file Post 302295455 by mjd_tech on Sunday 8th of March 2009 11:37:03 AM

03-08-2009

Registered User

ripat,

I knew there would be a better way, most likely awk.
Here, I try to explain how it works...

Code:

awk '
NR==FNR {_[NR]=$0}  
                    # NR is total number of lines read in both files.
                    # FNR is number of lines read, reset for each file.
                    # _[NR] is an array named _ with NR as index.
                    # This loads array with contents of file1,
                    # and ignores file2.
                    
NR!=FNR {print _[FNR] "\n" $0 "\n---"}
                    # This part ignores file1.
                    # For each line in file 2,
                    # Print the corresponding line from the array,
                    # using FNR as index.
                    # then a newline, then the line from file2,
                    # another newline, then the dashes, then another newline.
' file1 file2

Hopefully, this is a correct explanation.
I was initially confused by the _[NL] thing, thinking this was some kind of special awk reserved variable or something, but then I realized it's just an array named _
I guess that if file1 were super huge, you could run out of memory because it gets loaded into an array. There's probably a way to do this in perl that can handle huge files without slurping into an array...

Regards,
MD

mjd_tech

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LEARN ABOUT PLAN9

join

JOIN(1) 						      General Commands Manual							   JOIN(1)

NAME

       join - relational database operator

SYNOPSIS

       join [ options ] file1 file2

DESCRIPTION

       Join forms, on the standard output, a join of the two relations specified by the lines of file1 and file2.  If one of the file names is the
       standard input is used.

       File1 and file2 must be sorted in increasing ASCII collating sequence on the fields on which they are to be joined, normally the  first	in
       each line.

       There  is  one line in the output for each pair of lines in file1 and file2 that have identical join fields.  The output line normally con-
       sists of the common field, then the rest of the line from file1, then the rest of the line from file2.

       Input fields are normally separated spaces or tabs; output fields by space.  In this case, multiple separators count as	one,  and  leading
       separators are discarded.

       The following options are recognized, with POSIX syntax.

       -a n   In addition to the normal output, produce a line for each unpairable line in file n, where n is 1 or 2.

       -v n   Like -a, omitting output for paired lines.

       -e s   Replace empty output fields by string s.

       -1 m
       -2 m   Join on the mth field of file1 or file2.

       -jn m  Archaic equivalent for -n m.

       -ofields
	      Each  output  line  comprises the designated fields.  The comma-separated field designators are either 0, meaning the join field, or
	      have the form n.m, where n is a file number and m is a field number.  Archaic usage allows separate arguments for field designators.

       -tc    Use character c as the only separator (tab character) on input and output.  Every appearance of c in a line is significant.

EXAMPLES

       sort /adm/users | join -t: -a 1 -e "" - bdays
	      Add birthdays to password information, leaving unknown birthdays empty.  The layout of is given in users(6); bdays  contains  sorted
	      lines like

       tr : ' ' </adm/users | sort -k 3 3 >temp
       join -1 3 -2 3 -o 1.1,2.1 temp temp | awk '$1 < $2'
	      Print all pairs of users with identical userids.

SOURCE

       /sys/src/cmd/join.c

SEE ALSO

       sort(1), comm(1), awk(1)

BUGS

       With default field separation, the collating sequence is that of sort -b -ky,y; with -t, the sequence is that of sort -tx -ky,y.
       One of the files must be randomly accessible.

																	   JOIN(1)