如何验证程序是否存在,以返回错误并退出,或继续执行脚本?
看起来应该很容易,但这让我很为难。
如何验证程序是否存在,以返回错误并退出,或继续执行脚本?
看起来应该很容易,但这让我很为难。
当前回答
这将根据位置判断程序是否存在:
if [ -x /usr/bin/yum ]; then
echo "This is Centos"
fi
其他回答
我同意lhunath不鼓励使用which,他的解决方案对Bash用户完全有效。但是,为了更便于携带,应使用命令-v:
$ command -v foo >/dev/null 2>&1 || { echo "I require foo but it's not installed. Aborting." >&2; exit 1; }
命令命令符合POSIX。参见此处了解其规范:command-execute一个简单的命令
注意:类型符合POSIX,但类型-P不符合。
我使用这个,因为它非常简单:
if [ $(LANG=C type example 2>/dev/null | wc -l) = 1 ]; then
echo exists;
else
echo "not exists";
fi
or
if [ $(LANG=C type example 2>/dev/null | wc -l) = 1 ]; then
echo exists
else
echo "not exists"
fi
它使用shell内置程序和程序的回声状态进行标准输出,而不使用标准错误。另一方面,如果找不到命令,它只会将状态返回到标准错误。
仅zsh,但对于zsh脚本非常有用(例如,在编写完成脚本时):
zsh/parameter模块可以访问内部命令哈希表等。来自man zshmodules:
THE ZSH/PARAMETER MODULE
The zsh/parameter module gives access to some of the internal hash ta‐
bles used by the shell by defining some special parameters.
[...]
commands
This array gives access to the command hash table. The keys are
the names of external commands, the values are the pathnames of
the files that would be executed when the command would be in‐
voked. Setting a key in this array defines a new entry in this
table in the same way as with the hash builtin. Unsetting a key
as in `unset "commands[foo]"' removes the entry for the given
key from the command hash table.
尽管它是一个可加载的模块,但只要zsh不与--simulate一起使用,它似乎是默认加载的。
例子:
martin@martin ~ % echo $commands[zsh]
/usr/bin/zsh
要快速检查某个命令是否可用,只需检查哈希中是否存在密钥:
if (( ${+commands[zsh]} ))
then
echo "zsh is available"
fi
请注意,散列将包含$PATH文件夹中的任何文件,无论它们是否可执行。为了绝对确定,您必须对此进行统计:
if (( ${+commands[zsh]} )) && [[ -x $commands[zsh] ]]
then
echo "zsh is available"
fi
which命令可能有用。男子谁
如果找到可执行文件,则返回0;如果找不到或不可执行,则返回1:
NAME
which - locate a command
SYNOPSIS
which [-a] filename ...
DESCRIPTION
which returns the pathnames of the files which would
be executed in the current environment, had its
arguments been given as commands in a strictly
POSIX-conformant shell. It does this by searching
the PATH for executable files matching the names
of the arguments.
OPTIONS
-a print all matching pathnames of each argument
EXIT STATUS
0 if all specified commands are
found and executable
1 if one or more specified commands is nonexistent
or not executable
2 if an invalid option is specified
这样做的好处是,它可以确定可执行文件在运行环境中是否可用-这节省了一些问题。。。
剧本
#!/bin/bash
# Commands found in the hash table are checked for existence before being
# executed and non-existence forces a normal PATH search.
shopt -s checkhash
function exists() {
local mycomm=$1; shift || return 1
hash $mycomm 2>/dev/null || \
printf "\xe2\x9c\x98 [ABRT]: $mycomm: command does not exist\n"; return 1;
}
readonly -f exists
exists notacmd
exists bash
hash
bash -c 'printf "Fin.\n"'
后果
✘ [ABRT]: notacmd: command does not exist
hits command
0 /usr/bin/bash
Fin.