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Full Discussion: Bourne Shell - Problem with while loop variable scope.
Top Forums Shell Programming and Scripting Bourne Shell - Problem with while loop variable scope. Post 302476428 by DaveRich on Wednesday 1st of December 2010 04:04:27 PM
Old 12-01-2010
Bourne Shell - Problem with while loop variable scope.
Hello

I am having issues with a script I'm working on developing on a Solaris machine.

The script is intended to find out how many times a particular user (by given userid) has logged into the local system for more than one hour today.

Here is my while loop:
Code:
last $user | grep -v 'sshd' | grep -v 'still logged in' | grep "`date | cut -d' ' -f2-4`" | cut -d\( -f2 | cut -d: -f1 | while read numHours
do
        if [ $numHours -gt 0 ]; then
                numLogins=$(( $numLogins + 1 ))
                echo "$user logged in once for more than an hour ($numHours hours)." #DEBUG
        fi
done

I have declared numLogins before the loop, and the problem is after the loop I try and "echo $numLogins" but numLogins always contains 0. Even when my debug line prints out showing that the user has logged in for at least an hour.

I have determined that I believe this is because the while loop (when used in a pipeline) has a seperate variable scope, but I have tried rewriting my loop like:

Code:
while loop=read $line
do
        numHours=`echo $line | grep -v 'sshd' | grep -v 'still logged in' | grep "\`date | cut -d' ' -f2-4`" | cut -d\( -f2 | cut -d: -f1
        if [ $numHours -gt 0 ]; then
                numLogins=$(( $numLogins + 1 ))
                echo "$user logged in once for more than an hour ($numHours hours)." #DEBUG
        fi
done < `last $user`

I also thought it may be with the way I was incrementing my numLogins variable,
I have tried to use:
Code:
(( numLogins++ ))
using expr,
numLogins=`echo $numLogins + 1 | bc`

and a few other methods I can't quite remember.

Any help on this would be extremely appreciated.
Thanks a lot!
Last edited by DaveRich; 12-01-2010 at 05:10 PM..
 

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LEARN ABOUT OPENSOLARIS

cut

cut(1)								   User Commands							    cut(1)

NAME

       cut - cut out selected fields of each line of a file

SYNOPSIS

       cut -b list [-n] [file]...

       cut -c list [file]...

       cut -f list [-d delim] [-s] [file]...

DESCRIPTION

       Use the cut utility to cut out columns from a table or fields from each line of a file; in data base parlance, it implements the projection
       of a relation. The fields as specified by list can be fixed length, that is, character positions as on a punched card (-c  option)  or  the
       length can vary from line to line and be marked with a field delimiter character like TAB (-f option). cut can be used as a filter.

       Either the -b, -c, or -f option must be specified.

       Use grep(1) to make horizontal ``cuts'' (by context) through a file, or paste(1) to put files together column-wise (that is, horizontally).
       To reorder columns in a table, use cut and paste.

OPTIONS

       The following options are supported:

       list	    A comma-separated or blank-character-separated list of integer field numbers (in increasing order), with optional -  to  indi-
		    cate ranges (for instance, 1,4,7; 1-3,8; -5,10 (short for 1-5,10); or 3- (short for third through last field)).

       -b list	    The  list following -b specifies byte positions (for instance, -b1-72 would pass the first 72 bytes of each line). When -b and
		    -n are used together, list is adjusted so that no multi-byte character is split.

       -c list	    The list following -c specifies character positions (for instance, -c1-72 would pass the first 72 characters of each line).

       -d delim     The character following -d is the field delimiter (-f option only). Default is tab. Space or  other  characters  with  special
		    meaning to the shell must be quoted. delim can be a multi-byte character.

       -f list	    The  list  following  -f  is  a  list  of  fields  assumed to be separated in the file by a delimiter character (see -d ); for
		    instance, -f1,7 copies the first and seventh field only. Lines with no field delimiters will be passed through intact  (useful
		    for table subheadings), unless -s is specified.

       -n	    Do not split characters. When -b list and -n are used together, list is adjusted so that no multi-byte character is split.

       -s	    Suppresses	lines with no delimiter characters in case of -f option. Unless specified, lines with no delimiters will be passed
		    through untouched.

OPERANDS

       The following operands are supported:

       file	A path name of an input file. If no file operands are specified, or if a file operand is -, the standard input will be used.

USAGE

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

EXAMPLES

       Example 1 Mapping user IDs

       A mapping of user IDs to names follows:

	 example% cut -d: -f1,5 /etc/passwd

       Example 2 Setting current login name

       To set name to current login name:

	 example$ name=`who am i | cut -f1 -d' '`

ENVIRONMENT VARIABLES

       See environ(5) for descriptions of the following environment variables that affect the execution of cut: LANG,  LC_ALL,	LC_CTYPE,  LC_MES-
       SAGES, and NLSPATH.

EXIT STATUS

       The following exit values are returned:

       0      All input files were output successfully.

       >0     An error occurred.

ATTRIBUTES

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

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+
       |CSI			     |Enabled			   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       grep(1), paste(1), attributes(5), environ(5), largefile(5), standards(5)

DIAGNOSTICS

       cut: -n may only be used with -b

       cut: -d may only be used with -f

       cut: -s may only be used with -f

       cut: cannot open <file>

	   Either file cannot be read or does not exist.  If multiple files are present, processing continues.

       cut: no delimiter specified

	   Missing delim on -d option.

       cut: invalid delimiter

       cut: no list specified

	   Missing list on -b, -c, or -f option.

       cut: invalid range specifier

       cut: too many ranges specified

       cut: range must be increasing

       cut: invalid character in range

       cut: internal error processing input

       cut: invalid multibyte character

       cut: unable to allocate enough memory

SunOS 5.11							    29 Apr 1999 							    cut(1)
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