set –help
root@DESKTOP-6MVDBD1:~/go/src# set --help
set: set [-abefhkmnptuvxBCHP] [-o option-name] [--] [arg ...]
Set or unset values of shell options and positional parameters.
Change the value of shell attributes and positional parameters, or
display the names and values of shell variables.
Options:
-a Mark variables which are modified or created for export.
-b Notify of job termination immediately.
-e Exit immediately if a command exits with a non-zero status.
-f Disable file name generation (globbing).
-h Remember the location of commands as they are looked up.
-k All assignment arguments are placed in the environment for a
command, not just those that precede the command name.
-m Job control is enabled.
-n Read commands but do not execute them.
-o option-name
Set the variable corresponding to option-name:
allexport same as -a
braceexpand same as -B
emacs use an emacs-style line editing interface
errexit same as -e
errtrace same as -E
functrace same as -T
hashall same as -h
histexpand same as -H
history enable command history
ignoreeof the shell will not exit upon reading EOF
interactive-comments
allow comments to appear in interactive commands
keyword same as -k
monitor same as -m
noclobber same as -C
noexec same as -n
noglob same as -f
nolog currently accepted but ignored
notify same as -b
nounset same as -u
onecmd same as -t
physical same as -P
pipefail the return value of a pipeline is the status of
the last command to exit with a non-zero status,
or zero if no command exited with a non-zero status
posix change the behavior of bash where the default
operation differs from the Posix standard to
match the standard
privileged same as -p
verbose same as -v
vi use a vi-style line editing interface
xtrace same as -x
-p Turned on whenever the real and effective user ids do not match.
Disables processing of the $ENV file and importing of shell
functions. Turning this option off causes the effective uid and
gid to be set to the real uid and gid.
-t Exit after reading and executing one command.
-u Treat unset variables as an error when substituting.
-v Print shell input lines as they are read.
-x Print commands and their arguments as they are executed.
-B the shell will perform brace expansion
-C If set, disallow existing regular files to be overwritten
by redirection of output.
-E If set, the ERR trap is inherited by shell functions.
-H Enable ! style history substitution. This flag is on
by default when the shell is interactive.
-P If set, do not resolve symbolic links when executing commands
such as cd which change the current directory.
-T If set, the DEBUG and RETURN traps are inherited by shell functions.
-- Assign any remaining arguments to the positional parameters.
If there are no remaining arguments, the positional parameters
are unset.
- Assign any remaining arguments to the positional parameters.
The -x and -v options are turned off.
Using + rather than - causes these flags to be turned off. The
flags can also be used upon invocation of the shell. The current
set of flags may be found in $-. The remaining n ARGs are positional
parameters and are assigned, in order, to $1, $2, .. $n. If no
ARGs are given, all shell variables are printed.
Exit Status:
Returns success unless an invalid option is given.
set 简介
set指令能设置所使用shell的执行方式，可依照不同的需求来做设置。
常用方式
echo “$-“
root@DESKTOP-6MVDBD1:~/go/src# echo "$-"
himBHs # 显示当前shell开启的所有模式开关
root@DESKTOP-6MVDBD1:~/go/src# set -e
root@DESKTOP-6MVDBD1:~/go/src# echo "$-"
ehimBHs # 显示当前shell开启的所有模式开关
set -u
对于一些变量（如：APP）若忘记设置值，可能会导致 rm -rf /${APP} 变为 rm -rf /.。这是非常危险的操作。
开启 set -u 后执行脚本时，遇到不存在变量，bash报错并停止
root@DESKTOP-6MVDBD1:~/go/src# rm -rf ${APP}
root@DESKTOP-6MVDBD1:~/go/src# set -u
root@DESKTOP-6MVDBD1:~/go/src# rm -rf ${APP}
-bash: APP: unbound variable
set -x
在执行时打印命令及其参数。在调试 shell 脚本的时候很常用。
root@DESKTOP-6MVDBD1:~/go/src# set -x
root@DESKTOP-6MVDBD1:~/go/src# ls
+ ls --color=auto
github.com k8s.io mosn.io volcano.sh
set -o pipefail
set -e有一个例外情况，就是不适用于管道命令。
所谓管道命令，就是多个子命令通过管道运算符(|)组合成为一个大的命令。Bash 会把最后一个子命令的返回值，作为整个命令的返回值。也就是说，只要最后一个子命令不失败，管道命令总是会执行成功，因此它后面命令依然会执行，set -e就失效了。
请看下面这个例子
#!/bin/bash
set -e
foo | echo a
echo bar
执行结果如下。
$ bash script.sh
a
script.sh:行4: foo: 未找到命令
bar
上面代码中，foo是一个不存在的命令，但是foo | echo a这个管道命令会执行成功，导致后面的echo bar会继续执行。
set -o pipefail用来解决这种情况，只要一个子命令失败，整个管道命令就失败，脚本就会终止执行。
set -eo pipefail
foo | echo a
echo bar
运行后，结果如下
$ bash script.sh
a
script.sh:行4: foo: 未找到命令
可以看到，echo bar没有执行。
set +<参数>
使用 + 来替代 - 则代表关闭某个已经开启的选项
root@DESKTOP-6MVDBD1:~/go/src# set -x
root@DESKTOP-6MVDBD1:~/go/src# ls
+ ls --color=auto
github.com k8s.io mosn.io volcano.sh
root@DESKTOP-6MVDBD1:~/go/src# set +x
+ set +x
root@DESKTOP-6MVDBD1:~/go/src# ls
github.com k8s.io mosn.io volcano.sh
root@DESKTOP-6MVDBD1:~/go/src#
set -o
- 如果命令以非零状态退出，则立即退出。
- 替换时将未设置的变量视为错误。
- 管道的返回值是状态，最后一个以非零状态退出的命令，如果没有命令以非零状态退出，则为零。
set -o errexit
set -o nounset
set -o pipefail
附录
- https://github.com/kubernetes/kubernetes/blob/master/test/cmd/apply.sh#L17
- https://blog.51cto.com/linuy/170903
转载请注明来源，欢迎对文章中的引用来源进行考证，欢迎指出任何有错误或不够清晰的表达。可以在下面评论区评论，也可以邮件至 nz_nuaa@163.com