#Bash 的 env 命令
env [OPTION]... [-] [NAME=VALUE]... [COMMAND [ARG]...]
功能
创建新的环境运行程序。
类型
可执行文件（/usr/bin/env），属于 coreutils。
参数
OPTION选项：-i,--ignore-environment- 忽略原本的环境变量，从空的环境开始-0,--null- 以空字符（\0）作为行的结尾，而不是换行符（\n）-u,--unset=NAME- 删除环境变量NAME-C,--chdir=DIR- 切换工作目录-S,--split-string=S- 将S按空格拆分为独立的参数--block-signal[=SIG]- 阻止向执行的命令发送SIG信号--default-signal[=SIG]- 将SIG信号的处理方式重置为默认--ignore-signal[=SIG]- 将SIG信号的处理方式设为忽略--list-signal-handling- 将处理方式不为默认的所有信号在标准错误中列出-v,--debug- 打印每个处理步骤的详细信息--help- 显示帮助--version- 显示版本
-- 在所有选项之后，忽略原本的环境变量；同-i选项NAME=VALUE- 要设置的环境变量COMMAND- 要执行的命令，如果为空则打印所有环境变量ARG- 命令COMMAND的参数，在 shebang 行中需要使用-S选项
返回值
- 125 -
env命令自身失败 - 126 -
COMMAND无法被调用 - 127 -
COMMAND无法被找到 - 其它 -
COMMAND的返回值
#示例
设置环境变量
设置环境变量：
$ env NAME=Primers bash -c 'echo $NAME use $LANG'
Primers use en_US.UTF-8
$ NAME=Primers bash -c 'echo $NAME use $LANG' # 可以不使用 env
Primers use en_US.UTF-8
- 注意，这里不能直接写作
env NAME=Primers echo Hello $NAME，因为这样会在执行命令之前就将$NAME展开为空 - 单纯设置环境变量可以不使用
env，直接在命令前设置即可
清空并设置环境变量：
$ env -i NAME=Primers bash -c 'echo $NAME use $LANG'
Primers use
- 原有的环境变量被清空，因此
$LANG为空 - 可用于测试排除环境变量干扰
查看环境
$ env | grep PATH
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
$ env | grep -i proxy
ALL_PROXY=http://localhost:7890
#!/usr/bin/env -S
#!/usr/bin/env -S bash -c
echo Hello World
如果不使用 -S 选项，bash -c 会被视为一个整体命令而失败：
/usr/bin/env: ‘bash -c’: No such file or directory
/usr/bin/env: use -[v]S to pass options in shebang lines
#推荐阅读
#手册
ENV(1) User Commands ENV(1)
NAME
env - run a program in a modified environment
SYNOPSIS
env [OPTION]... [-] [NAME=VALUE]... [COMMAND [ARG]...]
DESCRIPTION
Set each NAME to VALUE in the environment and run COMMAND.
Mandatory arguments to long options are mandatory for short options
too.
-i, --ignore-environment
start with an empty environment
-0, --null
end each output line with NUL, not newline
-u, --unset=NAME
remove variable from the environment
-C, --chdir=DIR
change working directory to DIR
-S, --split-string=S
process and split S into separate arguments; used to pass multi‐
ple arguments on shebang lines
--block-signal[=SIG]
block delivery of SIG signal(s) to COMMAND
--default-signal[=SIG]
reset handling of SIG signal(s) to the default
--ignore-signal[=SIG]
set handling of SIG signal(s) to do nothing
--list-signal-handling
list non default signal handling to stderr
-v, --debug
print verbose information for each processing step
--help display this help and exit
--version
output version information and exit
A mere - implies -i. If no COMMAND, print the resulting environment.
SIG may be a signal name like 'PIPE', or a signal number like '13'.
Without SIG, all known signals are included. Multiple signals can be
comma-separated. An empty SIG argument is a no-op.
Exit status:
125 if the env command itself fails
126 if COMMAND is found but cannot be invoked
127 if COMMAND cannot be found
- the exit status of COMMAND otherwise
OPTIONS
-S/--split-string usage in scripts
The -S option allows specifying multiple parameters in a script. Run‐
ning a script named 1.pl containing the following first line:
#!/usr/bin/env -S perl -w -T
...
Will execute perl -w -T 1.pl .
Without the '-S' parameter the script will likely fail with:
/usr/bin/env: 'perl -w -T': No such file or directory
See the full documentation for more details.
--default-signal[=SIG] usage
This option allows setting a signal handler to its default action,
which is not possible using the traditional shell trap command. The
following example ensures that seq will be terminated by SIGPIPE no
matter how this signal is being handled in the process invoking the
command.
sh -c 'env --default-signal=PIPE seq inf | head -n1'
NOTES
POSIX's exec(3p) pages says:
"many existing applications wrongly assume that they start with
certain signals set to the default action and/or unblocked....
Therefore, it is best not to block or ignore signals across ex‐
ecs without explicit reason to do so, and especially not to
block signals across execs of arbitrary (not closely cooperat‐
ing) programs."
AUTHOR
Written by Richard Mlynarik, David MacKenzie, and Assaf Gordon.
REPORTING BUGS
GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
Report any translation bugs to <https://translationproject.org/team/>
COPYRIGHT
Copyright © 2023 Free Software Foundation, Inc. License GPLv3+: GNU
GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
SEE ALSO
sigaction(2), sigprocmask(2), signal(7)
Full documentation <https://www.gnu.org/software/coreutils/env>
or available locally via: info '(coreutils) env invocation'
GNU coreutils 9.4 April 2024 ENV(1)