我使用过的Linux命令之exit - 退出当前shell
用途说明
exit命令用于退出当前shell,在shell脚本中可以终止当前脚本执行。
常用参数
格式:exit n
退出。设置退出码为n。(Cause the shell to exit with a status of n.)
格式:exit
退出。退出码不变,即为最后一个命令的退出码。(If n is omitted, the exit status is that of the last command executed. )
格式:$?
上一个命令的退出码。
格式:trap "commands" EXIT
退出时执行commands指定的命令。( A trap on EXIT is executed before the shell terminates.)
退出码(exit status,或exit code)的约定:
0表示成功(Zero - Success)
非0表示失败(Non-Zero - Failure)
2表示用法不当(Incorrect Usage)
127表示命令没有找到(Command Not Found)
126表示不是可执行的(Not an executable)
>=128 信号产生
man 3 exit 写道
The C standard specifies two constants, EXIT_SUCCESS and EXIT_FAILURE, that may be passed to exit() to indicate
successful or unsuccessful termination, respectively.
以下摘自/usr/include/stdlib.h
1. #define EXIT_FAILURE 1 /* Failing exit status. */
2. #define EXIT_SUCCESS 0 /* Successful exit status. */
BSD试图对退出码标准化。
man 3 exit 写道
BSD has attempted to standardize exit codes; see the file <sysexits.h>.
以下摘自/usr/include/sysexits.h
1. #define EX_OK 0 /* successful termination */
2.
3. #define EX__BASE 64 /* base value for error messages */
4.
5. #define EX_USAGE 64 /* command line usage error */
6. #define EX_DATAERR 65 /* data format error */
7. #define EX_NOINPUT 66 /* cannot open input */
8. #define EX_NOUSER 67 /* addressee unknown */
9. #define EX_NOHOST 68 /* host name unknown */
10. #define EX_UNAVAILABLE 69 /* service unavailable */
11. #define EX_SOFTWARE 70 /* internal software error */
12. #define EX_OSERR 71 /* system error (e.g., can't fork) */
13. #define EX_OSFILE 72 /* critical OS file missing */
14. #define EX_CANTCREAT 73 /* can't create (user) output file */
15. #define EX_IOERR 74 /* input/output error */
16. #define EX_TEMPFAIL 75 /* temp failure; user is invited to retry */
17. #define EX_PROTOCOL 76 /* remote error in protocol */
18. #define EX_NOPERM 77 /* permission denied */
19. #define EX_CONFIG 78 /* configuration error */
20.
21. #define EX__MAX 78 /* maximum listed value */
使用示例
示例一 退出当前shell
[root@new55 ~]#
[root@new55 ~]# exit
logout
示例二 在脚本中,进入脚本所在目录,否则退出
1. cd $(dirname $0) || exit 1
示例三 在脚本中,判断参数数量,不匹配就打印使用方式,退出
1. if [ "$#" -ne "2"
2. "usage: $0 <area> <hours>"
3. 2
4. fi
示例四 在脚本中,退出时删除临时文件
1. trap "rm -f tmpfile; echo Bye."
示例五 检查上一命令的退出码
1. ./mycommand.sh
2. EXCODE=$?
3. if [ "$EXCODE" == "0"
4. "O.K"
5. fi