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Full Discussion: Removing lines from a file being used by another process using SHELL script
Top Forums Shell Programming and Scripting Removing lines from a file being used by another process using SHELL script Post 302705521 by Ygor on Tuesday 25th of September 2012 04:39:42 AM
Old 09-25-2012
I would guess that it depends on how you remove the top lines. This is at the bash prompt...
Code:
$ echo x > file1

$ ( ( echo a ; sleep 30 ; echo b ) | tee -a file1 ) &
[1] 7000

$ a


$ sed -i 1d file1
sed: cannot rename ./sedCDnEEq: Permission denied

$ cat file1
x
a

$ awk '{a[NR]=$0}END{close(FILENAME);for(i=2;i<=NR;i++)print a[i]>FILENAME}' file1

$ cat file1
a

$ b

[1]+  Done                    ( ( echo a; sleep 30; echo b ) | tee -a file1 )

$ cat file1
a
b

$

In the example above, I created a file then submitted a background process to append to the file. Using sed -i to remove the first line didn't work, but awk worked okay.
 

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LEARN ABOUT OPENSOLARIS

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 5.11							    3 Mar 2004								   comm(1)
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