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Full Discussion: Using AWK in a for loop
Top Forums Shell Programming and Scripting Using AWK in a for loop Post 302347292 by Jahn on Tuesday 25th of August 2009 10:32:25 AM
Old 08-25-2009
Using AWK in a for loop
Hello,

I am trying to use AWK to print only the first field of numerous text files, and then overwrite these files. They are of the format 1*2,3,4,5. I have tried the following code (using tcsh):

Code:
 foreach f (file1 file2 file3)
cat $f | awk -F'*' '{print $1}' > $f
end

However, I get very inconsistent results each time I run this script. I have tried creating a tmp directory where I run the above command on a clean set of the files. But, sometimes it returns empty files, whereas other times it runs fine for all the files. Any ideas on what is going on here, or if there is a better way to get awk to do what I want?

On a side note, I have tried a similar method using cut:

Code:
 foreach f (file1 file2 file3)
cat $f | cut -d'*' -f1 > $f
end

but I get the same inconsistencies.


Thank you for your help,

-Jahn
 

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LEARN ABOUT SUNOS

comm

comm(1) 							   User Commands							   comm(1)

NAME

       comm - select or reject lines common to two files

SYNOPSIS

       comm [-123] file1 file2

DESCRIPTION

       The comm utility reads file1 and file2, which must be ordered in the current collating sequence, and produces three text columns as output:
       lines only in file1; lines only in file2; and lines in both files.

       If the input files were ordered according to the collating sequence of the current locale, the lines  written  will  be	in  the  collating
       sequence of the original lines. If not, the results are unspecified.

OPTIONS

       The following options are supported:

       -1	Suppresses the output column of lines unique to file1.

       -2	Suppresses the output column of lines unique to file2.

       -3	Suppresses the output column of lines duplicated in file1 and file2.

OPERANDS

       The following operands are supported:

       file1	A path name of the first file to be compared. If file1 is -, the standard input is used.

       file2	A path name of the second file to be compared. If file2 is -, the standard input is used.

USAGE

       See largefile(5) for the description of the behavior of comm when encountering files greater than or equal to 2 Gbyte ( 2**31 bytes).

EXAMPLES

       Example 1: Printing a list of utilities specified by files

       If file1, file2, and file3 each contain a sorted list of utilities, the command

       example% comm -23 file1 file2  | comm -23 - file3

       prints a list of utilities in file1 not specified by either of the other files. The entry:

       example% comm -12 file1 file2 | comm -12 - file3

       prints a list of utilities specified by all three files. And the entry:

       example% comm -12  file2 file3 | comm -23 -file1

       prints a list of utilities specified by both file2 and file3, but not specified in file1.

ENVIRONMENT VARIABLES

       See  environ(5)	for  descriptions  of  the  following  environment  variables that affect the execution of comm: LANG, LC_ALL, LC_COLLATE,
       LC_CTYPE, LC_MESSAGES, and NLSPATH.

EXIT STATUS

       The following exit values are returned:

       0	All input files were successfully output as specified.

       >0	An error occurred.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWesu			   |
       +-----------------------------+-----------------------------+
       |CSI			     |enabled			   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       cmp(1), diff(1), sort(1), uniq(1), attributes(5), environ(5), largefile(5), standards(5)

SunOS 5.10							    3 Mar 2004								   comm(1)
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