Linux命令之exit – 退出当前shell

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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

C代码

#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

C代码

#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

Bash代码

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

Bash代码

if [ “$#” -ne “2” ]; then

echo “usage: $0

”

exit 2

示例四在脚本中，退出时删除临时文件

Bash代码

trap “rm -f tmpfile; echo Bye.” EXIT

示例五检查上一命令的退出码

Bash代码

./mycommand.sh

EXCODE=$?

if [ “$EXCODE” == “0” ]; then

echo “O.K”

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Linux命令之exit – 退出当前shell