04-17-2009
Writing files without temporary files
Hey Guys,
I was wondering if someone would give me a hand with an issue I'm having, let me explain the situation:
I have a file that is constantly being written to and read from with updated lines:
# cat activity.file
activity1
activity2
activity3
activity4
activity5
This file should never have more than 60 lines of text, so the "writing" process is as follows:
# tail -59 activity.file > temp; mv temp activity.file; echo "activityN" >> activity.file
Basically what this does is:
1.- Gets the bottom 59 files of activity.file into a temp file
2.- Renames the temp file into the original filename ( activity.file )
3.- Appends the new data in the bottom of the activity file.
So far this works great, but I'm trying to find a way to do the same procedure but without utilizing a temp file, as a "one-liner" as they say..
I tried the following:
tail -59 activity.file > activity.file ; echo "activityN" >> activity.file
But that didn't work...
Any ideas would be greatly appreciated
Thanks
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LEARN ABOUT LINUX
checkbashisms
CHECKBASHISMS(1) General Commands Manual CHECKBASHISMS(1)
NAME
checkbashisms - check for bashisms in /bin/sh scripts
SYNOPSIS
checkbashisms script ...
checkbashisms --help|--version
DESCRIPTION
checkbashisms, based on one of the checks from the lintian system, performs basic checks on /bin/sh shell scripts for the possible presence
of bashisms. It takes the names of the shell scripts on the command line, and outputs warnings if possible bashisms are detected.
Note that the definition of a bashism in this context roughly equates to "a shell feature that is not required to be supported by POSIX";
this means that some issues flagged may be permitted under optional sections of POSIX, such as XSI or User Portability.
In cases where POSIX and Debian Policy disagree, checkbashisms by default allows extensions permitted by Policy but may also provide
options for stricter checking.
OPTIONS
--help, -h
Show a summary of options.
--newline, -n
Check for "echo -n" usage (non POSIX but required by Debian Policy 10.4.)
--posix, -p
Check for issues which are non POSIX but required to be supported by Debian Policy 10.4 (implies -n).
--force, -f
Force each script to be checked, even if it would normally not be (for instance, it has a bash or non POSIX shell shebang or appears
to be a shell wrapper).
--extra, -x
Highlight lines which, whilst they do not contain bashisms, may be useful in determining whether a particular issue is a false posi-
tive which may be ignored. For example, the use of "$BASH_ENV" may be preceded by checking whether "$BASH" is set.
--version, -v
Show version and copyright information.
EXIT VALUES
The exit value will be 0 if no possible bashisms or other problems were detected. Otherwise it will be the sum of the following error val-
ues:
1 A possible bashism was detected.
2 A file was skipped for some reason, for example, because it was unreadable or not found. The warning message will give details.
SEE ALSO
lintian(1).
AUTHOR
checkbashisms was originally written as a shell script by Yann Dirson <dirson@debian.org> and rewritten in Perl with many more features by
Julian Gilbey <jdg@debian.org>.
DEBIAN Debian Utilities CHECKBASHISMS(1)