linux之exit

原文链接：http://codingstandards.iteye.com/blog/836625   （转载请注明出处）

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

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

#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 */

#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

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

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

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

示例四 在脚本中，退出时删除临时文件

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

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

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