2015-4-8

1, in the shell,-f is to determine whether the file exists,-D is to determine whether the path exists.

2, the shell and programming language, like writing, to take the judgment statement, that is, logic.

3. Write a simple shell script to empty the system log:

1 #!/bin/bash2 3 #Clear Log Script4 5log_dir=/var/Log6 7Log_name=Messages8 9Root_uid=0#The user has the root user permission when the $UID is 0Ten  One #determine if the user is the root user A if[$UID-ne $ROOT _uid] -  Then -Echo"must is root to run this script." theExit 1 - fi -  - #determine if a directory exists +CD $LOG _dir | | { -Echo"cannot change to necessary directory.">&2 +Exit 1 A } at  - #determine if a file exists - if[ ! -F $LOG _name] -  Then -Echo"Log file not exist.">&2 -Exit 1 in fi -  toCat/dev/null > $LOG _name && Echo"Logs cleaned up."                                                                                                  +  -Exit 0

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2015-4-8