Linux命令之exit
原文链接：http://codingstandards.iyunv.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 thelastcommand 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_UNAVAILABLE69 /* 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_UNAVAILABLE69 /* 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
# # 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
问题思考
相关资料
【1】91linux Linux exit 命令 【2】曲径通幽 [概念]exit n 【3】Linux大学Bash Shell Exit Status Tutorial with Practical Examples
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