Linux命令之exit - 退出当前shell【返回值状态】

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.  */ 

#define EXIT_FAILURE    1       /* Failing exit status.  */#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 */ 

#define EX_OK           0       /* successful termination */#define EX__BASE        64      /* base value for error messages */#define EX_USAGE        64      /* command line usage error */#define EX_DATAERR      65      /* data format error */#define EX_NOINPUT      66      /* cannot open input */#define EX_NOUSER       67      /* addressee unknown */#define EX_NOHOST       68      /* host name unknown */#define EX_UNAVAILABLE  69      /* service unavailable */#define EX_SOFTWARE     70      /* internal software error */#define EX_OSERR        71      /* system error (e.g., can't fork) */#define EX_OSFILE       72      /* critical OS file missing */#define EX_CANTCREAT    73      /* can't create (user) output file */#define EX_IOERR        74      /* input/output error */#define EX_TEMPFAIL     75      /* temp failure; user is invited to retry */#define EX_PROTOCOL     76      /* remote error in protocol */#define EX_NOPERM       77      /* permission denied */#define EX_CONFIG       78      /* configuration error */#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 

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" ]; then 
2.     echo "usage: $0 <area> <hours>" 
3.     exit 2 
4. fi 

if [ "$#" -ne "2" ]; then    echo "usage: $0 <area> <hours>"    exit 2fi

 

示例四 在脚本中，退出时删除临时文件

1. trap "rm -f tmpfile; echo Bye." EXIT 

trap "rm -f tmpfile; echo Bye." EXIT

 

示例五 检查上一命令的退出码

1. ./mycommand.sh 
2. EXCODE=$? 
3. if [ "$EXCODE" == "0" ]; then 
4.     echo "O.K" 
5. fi 

./mycommand.shEXCODE=$?if [ "$EXCODE" == "0" ]; then    echo "O.K"fi