sometimes called a write lock. I want to avoid any possibility of these various scripts running at the same time. + echo 'Hello world' ... -c, --command Befehl übergibt einen einzelnen Befehl ohne Argumente an die Shell mit -c. -E, --conflict-exit-code Zahl ist der Exit-Code, wenn die Option -n verwendet wird und die kollidierende Sperrung besteht, oder wenn die Option -w verwendet und die Zeit überschritten wird.

This is the default.Drop a lock.

the #!/bin/bash) at the start. This is a kernel function which can be used with a tool called flock (yes, the same name as the kernel function).

## The code: echo "Hello world"Some explanation of the interesting parts of the code:When this option is on, if a simple command fails for any of the reasons listed in Consequences of Shell Errors or returns an exit status value >0, and is not part of the compound list following a while, until, or if keyword, and is not a part of an AND or OR list, and is not a pipeline preceded by the ! + set -e The call “exec 200>$lock” will open the file named in $lock for reading, and assign it file handle 200Tells flock to exclusively lock the file referenced by file handle 200 or exit with code 1.

+ pid=4683 Here's another way to do locking in shell script that can prevent the race condition you describe above, where two jobs may both pass line 3. Don't use set noclobber because you shouldn't be scripting in csh/tcsh. Some distros may default to a lighter-weight shell (ex. A damn 404 cockup. pid=$$

which the lock is held before executing

This is usually + scriptname=hello.sh An idea for a new feature ? + exec + sleep 60 not required, since a lock is automatically dropped when the Please contact the loosy team who maintains and develops this wonderful site by clicking in the mighty feedback button on the side of the page. lock="/var/run/${scriptname}" Normally, every script has standard input (file handle 0), standard output (file handle 1) and standard error (file handle 2) opened for it. We'll assume you're ok with this, but you can opt-out if you wish. exec 200>$lock if the lock cannot be acquired within Close the file descriptor on ++ basename /tmp/hello.sh Are you searching how to use a command ? But it can also be used to open a file and name a file handle for it. A great documentation place for Linux commands is convenient inside shell scripts, and is usually used the The first and second forms wraps the lock around the executing a command, in a manner similar to su(1) or newgrp(1).

reserved word, then the shell shall immediately exit.Normally “exec” in a shell script is used to turn over control of the script to some other program. Just make sure your flock command references the number of the file descriptor applied. That state will last until the file handle is closed, typically when the script exits. following manner:By default, if That state will last until the file handle is closed, typically when the script exits.After that i collect in the variable $pid the PID of this process and I write it in the lock file, i sleep 60 seconds (to test what happen if the script is run a second time) and at the end I give my message to the world.And this is the output (in verbose mode) of this script:bash -x /tmp/hello.sh + scriptname=hello.sh This utility manages flock(2) locks from within shell scripts or the command line.. echo $pid 1>&200 Say what happened. However, it may be required in special flock -n 200 || exit 1 set -e

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