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File name : wait

Content :wait [ job ... ] Wait for the specified jobs or processes. If job is not given then all currently active child processes are waited for. Each job can be either a job specification or the process ID of a job in the job table. The exit status from this command is that of the job waited for. If job represents an unknown job or process ID, a warning is printed (unless the POSIX_BUILTINS option is set) and the exit status is 127. It is possible to wait for recent processes (specified by process ID, not by job) that were running in the background even if the process has exited. Typically the process ID will be recorded by capturing the value of the variable $! immediately after the process has been started. There is a limit on the number of process IDs remembered by the shell; this is given by the value of the system configuration parameter CHILD_MAX. When this limit is reached, older process IDs are discarded, least recently started processes first. Note there is no protection against the process ID wrapping, i.e. if the wait is not executed soon enough there is a chance the process waited for is the wrong one. A conflict implies both process IDs have been generated by the shell, as other pro- cesses are not recorded, and that the user is potentially inter- ested in both, so this problem is intrinsic to process IDs.

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