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Full Discussion: How to Lock the Script?
Top Forums UNIX for Dummies Questions & Answers How to Lock the Script? Post 302876534 by chacko193 on Monday 25th of November 2013 09:16:41 AM
Old 11-25-2013
One more way to do it

Code:
#!/bin/sh

myPid=$$
scriptName=$(basename $0)
lockFile=/tmp/${scriptName}.pid

#Check if the lockfile exists. If yes check if the process that locked exists
if [ -f ${lockFile} ] 
then
  pid=$(cat $lockFile)
  if ps -ef | grep -v grep | grep -q ${pid}
  then
    echo "An earlier instance of the script ${scriptName} is running with pid ${pid}."
    exit 1
  else  #The script has exited without removing the lock file.
    rm ${lockFile}
fi

#Now create the new lockfile
echo ${myPid} >$l{lockFile}

Make sure that you remove the lock file when you exit.(Both planned and unplanned exit)
This User Gave Thanks to chacko193 For This Post:
 

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mkfifo(1)						      General Commands Manual							 mkfifo(1)

NAME
mkfifo - Makes FIFO special files SYNOPSIS
mkfifo [-m mode] file... The mkfifo utility creates FIFO special files in the order specified. STANDARDS
Interfaces documented on this reference page conform to industry standards as follows: mkfifo: XCU5.0 Refer to the standards(5) reference page for more information about industry standards and associated tags. OPTIONS
Sets the file permission bits of the new file to the specified mode value, after creating the FIFO special file. The mode argument is a symbolic mode string (see chmod), in which the operator characters + (plus sign) and - (minus) are interpreted relative to the default file mode for that file type. The + character adds permissions to the default mode, and - deletes permissions from the default mode. [Tru64 UNIX] The default mode is a=rw (permissions of rw-rw-rw) as modified by the current file mode creation mask (umask). OPERANDS
The path name of a FIFO special file to be created. DESCRIPTION
For each file argument, mkfifo performs actions equivalent to the mkfifo() call with the following arguments: The file argument is used as the pathname argument. If the -m option is not used, the value of the bitwise inclusive OR of S_IRUSR, S_IWUSR, S_IRGRP, S_IWGRP, S_IROTH, and S_IWOTH is used as the mode argument. EXIT STATUS
The mkfifo utility exits with one of the following values: Indicates that all the specified FIFO special files were created successfully. Indicates that an error occurred. EXAMPLES
To create a FIFO special file with permissions prw-r--r--, enter: mkfifo -m 644 /tmp/myfifo The command creates the /tmp/myfifo file with read/write permissions for the owner and read permission for the group and for others. To create a FIFO special file using the - (minus) operand to set permissions of prw-r-----, enter: mkfifo -m g-w,o-rw /tmp/fifo2 The command creates the /tmp/fifo2 file, removing write permission for the group and all permissions for others. ENVIRONMENT VARIABLES
The following environment variables affect the execution of mkfifo: Provides a default value for the internationalization variables that are unset or null. If LANG is unset or null, the corresponding value from the default locale is used. If any of the internationalization variables contain an invalid setting, the utility behaves as if none of the variables had been defined. If set to a non-empty string value, overrides the values of all the other internationalization variables. Determines the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multibyte characters in arguments). Determines the locale for the format and contents of diagnostic messages written to standard error. Determines the location of message catalogues for the processing of LC_MESSAGES. SEE ALSO
Commands: mkdir(1), mknod(8) Functions: chmod(2), mkdir(2), mkfifo(3), mknod(2), umask(2) Standards: standards(5) mkfifo(1)
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