tail head cat sleep
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Manual Pages  — SLEEP


sleep – suspend execution for an interval of time



sleep seconds


The sleep command suspends execution for a minimum of seconds.

If the sleep command receives a signal, it takes the standard action. When the SIGINFO signal is received, the estimate of the amount of seconds left to sleep is printed on the standard output.


The SIGALRM signal is not handled specially by this implementation.

The sleep command allows and honors a non-integer number of seconds to sleep in any form acceptable by strtod(3). This is a non-portable extension, and its use will nearly guarantee that a shell script will not execute properly on another system.


The utility exits 0 on success, and >0 if an error occurs.


To schedule the execution of a command for x number seconds later (with csh(1)):

    (sleep 1800; sh command_file >& errors)&

This incantation would wait a half hour before running the script command_file. (See the at(1) utility.)

To reiteratively run a command (with the csh(1)):

while (1)
        if (! -r zzz.rawdata) then
                sleep 300
                foreach i (`ls *.rawdata`)
                        sleep 70
                        awk -f collapse_data $i >> results

The scenario for a script such as this might be: a program currently running is taking longer than expected to process a series of files, and it would be nice to have another program start processing the files created by the first program as soon as it is finished (when zzz.rawdata is created). The script checks every five minutes for the file zzz.rawdata, when the file is found, then another portion processing is done courteously by sleeping for 70 seconds in between each awk job.


nanosleep(2), sleep(3)


The sleep command is expected to be IEEE Std 1003.2 ("POSIX.2") compatible.


A sleep command appeared in AT&T v4 .

SLEEP (1) April 18, 1994

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"I liken starting one's computing career with Unix, say as an undergraduate, to being born in East Africa. It is intolerably hot, your body is covered with lice and flies, you are malnourished and you suffer from numerous curable diseases. But, as far as young East Africans can tell, this is simply the natural condition and they live within it. By the time they find out differently, it is too late. They already think that the writing of shell scripts is a natural act."
— Ken Pier, Xerox PARC