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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 OSX

script

SCRIPT(1)						    BSD General Commands Manual 						 SCRIPT(1)

NAME

     script -- make typescript of terminal session

SYNOPSIS

     script [-akq] [-t time] [file [command ...]]

DESCRIPTION

     The script utility makes a typescript of everything printed on your terminal.  It is useful for students who need a hardcopy record of an
     interactive session as proof of an assignment, as the typescript file can be printed out later with lpr(1).

     If the argument file is given, script saves all dialogue in file.	If no file name is given, the typescript is saved in the file typescript.

     If the argument command is given, script will run the specified command with an optional argument vector instead of an interactive shell.

     The following options are available:

     -a      Append the output to file or typescript, retaining the prior contents.

     -k      Log keys sent to program as well as output.

     -q      Run in quiet mode, omit the start and stop status messages.

     -t time
	     Specify time interval between flushing script output file.  A value of 0 causes script to flush for every character I/O event.  The
	     default interval is 30 seconds.

     The script ends when the forked shell (or command) exits (a control-D to exit the Bourne shell (sh(1)), and exit, logout or control-D (if
     ignoreeof is not set) for the C-shell, csh(1)).

     Certain interactive commands, such as vi(1), create garbage in the typescript file.  The script utility works best with commands that do not
     manipulate the screen.  The results are meant to emulate a hardcopy terminal, not an addressable one.

ENVIRONMENT

     The following environment variable is utilized by script:

     SHELL  If the variable SHELL exists, the shell forked by script will be that shell.  If SHELL is not set, the Bourne shell is assumed.  (Most
	    shells set this variable automatically).

SEE ALSO

     csh(1) (for the history mechanism).

HISTORY

     The script command appeared in 3.0BSD.

BUGS

     The script utility places everything in the log file, including linefeeds and backspaces.	This is not what the naive user expects.

     It is not possible to specify a command without also naming the script file because of argument parsing compatibility issues.

     When running in -k mode, echo cancelling is far from ideal.  The slave terminal mode is checked for ECHO mode to check when to avoid manual
     echo logging.  This does not work when in a raw mode where the program being run is doing manual echo.

BSD
								 January 22, 2004							       BSD
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