blocks|key|1352577|text|您可以使用ENV散列访问系统环境变量：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1352578|puts+ENV['PATH']|code-block|syntax|javascript|1352579|它将返回系统上的路径。因此，如果你想知道程序nmap是否存在，你可以这样做：|offset|length|style|CODE|1352580|ENV['PATH'].split(':').each+{%7Cfolder%7C+puts+File.exists?(folder%2B'/nmap')}|1352581|如果找到文件，这将打印true，否则将打印false。|1352582|entityMap^0|0|0|M|4|0|0|B|4|L|5|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@$I|V|J|W|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|Y|8|@$I|Z|J|10|K|L]|$I|11|J|12|K|L]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|R|$]]

You can access system environment variables with the ENV hash:

<pre><code>puts ENV['PATH']
</code></pre>

It will return the PATH on your system. So if you want to know if program <code>nmap</code> exists, you can do this:

<pre><code>ENV['PATH'].split(':').each {|folder| puts File.exists?(folder+'/nmap')}
</code></pre>

This will print <code>true</code> if file was found or <code>false</code> otherwise.

blocks|key|1352639|text|有一个名为which_ruby的GEM，它是一个纯Ruby的实现。它不再可用。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1352640|然而，我找到了这个pure-Ruby+alternative+implementation。|1352641|entityMap|0|LINK|mutability|MUTABLE|url|http://github.com/vertiginous/pik/blob/master/lib/pik/which.rb^0|5|A|0|9|10|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|S|8|@]|D|@$9|T|A|U|1|V]]|E|$]]|$1|H|3|-4|5|6|7|W|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

There was a GEM called <code>which_ruby</code>that was a pure-Ruby which implementation.
It's no longer available.

However, I found this <a href="http://github.com/vertiginous/pik/blob/master/lib/pik/which.rb" rel="nofollow noreferrer">pure-Ruby alternative implementation</a>.

blocks|key|1137382|text|这是对rogeriopvl答案的一个调整，使其跨平台：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1137383|require+'rbconfig'

def+is_windows?
++Config::CONFIG["host_os"]+=~+/mswin%7Cmingw/
end

def+exists_in_path?(file)
++entries+=+ENV['PATH'].split(is_windows?+?+";"+:+":")
++entries.any?+{%7Cf%7C+File.exists?("#{f}/#{file}")}
end|code-block|syntax|javascript|1137384|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

This is a tweak of rogeriopvl's answer, making it cross platform:

<pre><code>require 'rbconfig'

def is_windows?
 Config::CONFIG["host_os"] =~ /mswin|mingw/
end

def exists_in_path?(file)
 entries = ENV['PATH'].split(is_windows? ? ";" : ":")
 entries.any? {|f| File.exists?("#{f}/#{file}")}
end
</code></pre>

blocks|key|1137455|text|def+command?(name)
++`which+#{name}`
++$?.success?
end|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1137456|最初取自hub，它使用type+-t而不是which+(对于我来说，这对zsh和bash都是失败的)。|unstyled|offset|length|style|CODE|1137457|entityMap|0|LINK|mutability|MUTABLE|url|http://github.com/defunkt/hub^0|0|B|7|L|5|4|3|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|T|8|@$G|U|H|V|I|J]|$G|W|H|X|I|J]]|9|@$G|Y|H|Z|1|10]]|A|$]]|$1|K|3|-4|5|F|7|11|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

<pre><code>def command?(name)
 `which #{name}`
 $?.success?
end
</code></pre>

Initially taken from <a href="http://github.com/defunkt/hub" rel="noreferrer">hub</a>, which used <code>type -t</code> instead of <code>which</code> though (and which failed for both zsh and bash for me).

blocks|key|1352875|text|这是我正在使用的。这是平台中立的(File::PATH_SEPARATOR在Unix上是":"，在Windows上是";"+)，只查找实际可由当前进程的有效用户执行的程序文件，并在找到程序后立即终止：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1352876|##
#+Returns+%2Btrue%2B+if+the+%2Bprogram%2B+executable+is+found+in+the+user's+path.
def+has_program?(program)
++ENV['PATH'].split(File::PATH_SEPARATOR).any?+do+%7Cdirectory%7C
++++File.executable?(File.join(directory,+program.to_s))
++end
end|code-block|syntax|javascript|1352877|entityMap^0|H|K|18|3|1M|3|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|U|8|@]|D|@]|E|$]]]|L|$]]

Here's what I'm using. This is platform neutral (<code>File::PATH_SEPARATOR</code> is <code>":"</code> on Unix and <code>";"</code> on Windows), only looks for program files that actually are executable by the effective user of the current process, and terminates as soon as the program is found:

<pre><code>##
# Returns +true+ if the +program+ executable is found in the user's path.
def has_program?(program)
 ENV['PATH'].split(File::PATH_SEPARATOR).any? do |directory|
 File.executable?(File.join(directory, program.to_s))
 end
end
</code></pre>

blocks|key|1352913|text|我想补充的是，which采用静默模式的标志-s，它只设置成功标志，消除了重定向输出的需要。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1352914|entityMap^0|7|5|L|2|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

I'd like to add that <code>which</code> takes the flag <code>-s</code> for silent mode, which only sets the success flag, removing the need for redirecting the output.

blocks|key|1137672|text|真正的跨平台解决方案，在Windows上正常工作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1137673|#+Cross-platform+way+of+finding+an+executable+in+the+$PATH.
#
#+++which('ruby')+#=>+/usr/bin/ruby
def+which(cmd)
++exts+=+ENV['PATHEXT']+?+ENV['PATHEXT'].split(';')+:+['']
++ENV['PATH'].split(File::PATH_SEPARATOR).each+do+%7Cpath%7C
++++exts.each+do+%7Cext%7C
++++++exe+=+File.join(path,+"#{cmd}#{ext}")
++++++return+exe+if+File.executable?(exe)+&&+!File.directory?(exe)
++++end
++end
++nil
end|code-block|syntax|javascript|1137674|这不使用主机操作系统嗅探，并尊重$PATHEXT，它列出了Windows上可执行文件的有效文件扩展名。|1137675|which可以在许多系统上运行，但不是所有系统都可以运行。|offset|length|style|CODE|1137676|entityMap^0|0|0|0|0|5|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|T|8|@$K|U|L|V|M|N]]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

True cross-platform solution, works properly on Windows:

<pre><code># Cross-platform way of finding an executable in the $PATH.
#
# which('ruby') #=&gt; /usr/bin/ruby
def which(cmd)
 exts = ENV['PATHEXT'] ? ENV['PATHEXT'].split(';') : ['']
 ENV['PATH'].split(File::PATH_SEPARATOR).each do |path|
 exts.each do |ext|
 exe = File.join(path, "#{cmd}#{ext}")
 return exe if File.executable?(exe) &amp;&amp; !File.directory?(exe)
 end
 end
 nil
end
</code></pre>

This doesn't use host OS sniffing, and respects $PATHEXT which lists valid file extensions for executables on Windows.

Shelling out to <code>which</code> works on many systems but not all.

blocks|key|1137700|text|基于rogeriovl的解决方案，但通过执行测试而不是存在测试来完成功能。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1137701|def+command_exists?(command)
++ENV['PATH'].split(':').each+{%7Cfolder%7C+File.executable?(File.join(folder,+command))}
end|code-block|syntax|javascript|1137702|仅适用于UNIX+(Windows不使用冒号作为分隔符)|1137703|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Solution based on rogeriovl, but complete function with execution test rather than existence test.

<pre><code>def command_exists?(command)
 ENV['PATH'].split(':').each {|folder| File.executable?(File.join(folder, command))}
end
</code></pre>

Will work only for UNIX (Windows does not use colon as a separator)

blocks|key|1137770|text|在linux上，我使用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1137771|exists+=+`which+#{command}`.size.>(0)|code-block|syntax|javascript|1137772|不幸的是，which不是一个POSIX命令，因此在Mac、BSD等上的行为是不同的(即，如果找不到命令就会抛出一个错误)。也许最理想的解决方案是使用|offset|length|style|CODE|1137773|`command+-v+#{command}`.size.>(0)++#+fails!:+ruby+can't+access+built-in+functions|1137774|但这失败了，因为ruby似乎不能访问内置函数。但command+-v将是实现这一点的POSIX方式。|1137775|entityMap^0|0|0|5|5|0|0|O|A|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@$I|V|J|W|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|Y|8|@$I|Z|J|10|K|L]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|R|$]]

On linux I use:

<pre><code>exists = `which #{command}`.size.&gt;(0)
</code></pre>

Unfortunately, <code>which</code> is not a POSIX command and so behaves differently on Mac, BSD, etc (i.e., throws an error if the command is not found). Maybe the ideal solution would be to use 

<pre><code>`command -v #{command}`.size.&gt;(0) # fails!: ruby can't access built-in functions
</code></pre>

But this fails because ruby seems to not be capable of accessing built-in functions. But <code>command -v</code> would be the POSIX way to do this.

blocks|key|1353063|text|使用stdlib附带的mkmf中的find_executable方法。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1353064|require+'mkmf'

find_executable+'ruby'
#=>+"/Users/narkoz/.rvm/rubies/ruby-2.0.0-p0/bin/ruby"

find_executable+'which-ruby'
#=>+nil|code-block|syntax|javascript|1353065|entityMap|0|LINK|mutability|MUTABLE|url|http://www.ruby-doc.org/stdlib-2.0.0/libdoc/mkmf/rdoc/MakeMakefile.html#method-i-find_executable^0|B|4|H|F|H|F|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@$9|X|A|Y|1|Z]]|E|$]]|$1|F|3|G|5|H|7|10|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|L|$M|$5|N|O|P|E|$Q|R]]]]

Use <a href="http://www.ruby-doc.org/stdlib-2.0.0/libdoc/mkmf/rdoc/MakeMakefile.html#method-i-find_executable"><code>find_executable</code></a> method from <code>mkmf</code> which is included to stdlib.

<pre><code>require 'mkmf'

find_executable 'ruby'
#=&gt; "/Users/narkoz/.rvm/rubies/ruby-2.0.0-p0/bin/ruby"

find_executable 'which-ruby'
#=&gt; nil
</code></pre>

blocks|key|1137824|text|这是一个基于@mislav's+answer的改进版本。这将允许任何类型的路径输入，并严格遵循cmd.exe如何选择要在Windows中执行的文件。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1137825|#+which(cmd)+::+string+or+nil
#
#+Multi-platform+implementation+of+"which".
#+It+may+be+used+with+UNIX-based+and+DOS-based+platforms.
#
#+The+argument+can+not+only+be+a+simple+command+name+but+also+a+command+path
#+may+it+be+relative+or+complete.
#
def+which(cmd)
++raise+ArgumentError.new("Argument+not+a+string:+#{cmd.inspect}")+unless+cmd.is_a?(String)
++return+nil+if+cmd.empty?
++case+RbConfig::CONFIG['host_os']
++when+/cygwin/
++++exts+=+nil
++when+/dos%7Cmswin%7C%5Ewin%7Cmingw%7Cmsys/
++++pathext+=+ENV['PATHEXT']
++++exts+=+pathext+?+pathext.split(';').select{+%7Ce%7C+e[0]+==+'.'+}+:+['.com',+'.exe',+'.bat']
++else
++++exts+=+nil
++end
++if+cmd[File::SEPARATOR]+or+(File::ALT_SEPARATOR+and+cmd[File::ALT_SEPARATOR])
++++if+exts
++++++ext+=+File.extname(cmd)
++++++if+not+ext.empty?+and+exts.any?{+%7Ce%7C+e.casecmp(ext).zero?+}+\
++++++and+File.file?(cmd)+and+File.executable?(cmd)
++++++++return+File.absolute_path(cmd)
++++++end
++++++exts.each+do+%7Cext%7C
++++++++exe+=+"#{cmd}#{ext}"
++++++++return+File.absolute_path(exe)+if+File.file?(exe)+and+File.executable?(exe)
++++++end
++++else
++++++return+File.absolute_path(cmd)+if+File.file?(cmd)+and+File.executable?(cmd)
++++end
++else
++++paths+=+ENV['PATH']
++++paths+=+paths+?+paths.split(File::PATH_SEPARATOR).select{+%7Ce%7C+File.directory?(e)+}+:+[]
++++if+exts
++++++ext+=+File.extname(cmd)
++++++has_valid_ext+=+(not+ext.empty?+and+exts.any?{+%7Ce%7C+e.casecmp(ext).zero?+})
++++++paths.unshift('.').each+do+%7Cpath%7C
++++++++if+has_valid_ext
++++++++++exe+=+File.join(path,+"#{cmd}")
++++++++++return+File.absolute_path(exe)+if+File.file?(exe)+and+File.executable?(exe)
++++++++end
++++++++exts.each+do+%7Cext%7C
++++++++++exe+=+File.join(path,+"#{cmd}#{ext}")
++++++++++return+File.absolute_path(exe)+if+File.file?(exe)+and+File.executable?(exe)
++++++++end
++++++end
++++else
++++++paths.each+do+%7Cpath%7C
++++++++exe+=+File.join(path,+cmd)
++++++++return+File.absolute_path(exe)+if+File.file?(exe)+and+File.executable?(exe)
++++++end
++++end
++end
++nil
end|code-block|syntax|javascript|1137826|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/5471032/445221^0|1B|7|6|G|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@$9|V|A|W|1|X]]|E|$]]|$1|F|3|G|5|H|7|Y|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|L|$M|$5|N|O|P|E|$Q|R]]]]

This is an improved version based on <a href="https://stackoverflow.com/a/5471032/445221">@mislav's answer</a>. This would allow any type of path input and strictly follows how <code>cmd.exe</code> chooses the file to execute in Windows.

<pre><code># which(cmd) :: string or nil
#
# Multi-platform implementation of "which".
# It may be used with UNIX-based and DOS-based platforms.
#
# The argument can not only be a simple command name but also a command path
# may it be relative or complete.
#
def which(cmd)
 raise ArgumentError.new("Argument not a string: #{cmd.inspect}") unless cmd.is_a?(String)
 return nil if cmd.empty?
 case RbConfig::CONFIG['host_os']
 when /cygwin/
 exts = nil
 when /dos|mswin|^win|mingw|msys/
 pathext = ENV['PATHEXT']
 exts = pathext ? pathext.split(';').select{ |e| e[0] == '.' } : ['.com', '.exe', '.bat']
 else
 exts = nil
 end
 if cmd[File::SEPARATOR] or (File::ALT_SEPARATOR and cmd[File::ALT_SEPARATOR])
 if exts
 ext = File.extname(cmd)
 if not ext.empty? and exts.any?{ |e| e.casecmp(ext).zero? } \
 and File.file?(cmd) and File.executable?(cmd)
 return File.absolute_path(cmd)
 end
 exts.each do |ext|
 exe = "#{cmd}#{ext}"
 return File.absolute_path(exe) if File.file?(exe) and File.executable?(exe)
 end
 else
 return File.absolute_path(cmd) if File.file?(cmd) and File.executable?(cmd)
 end
 else
 paths = ENV['PATH']
 paths = paths ? paths.split(File::PATH_SEPARATOR).select{ |e| File.directory?(e) } : []
 if exts
 ext = File.extname(cmd)
 has_valid_ext = (not ext.empty? and exts.any?{ |e| e.casecmp(ext).zero? })
 paths.unshift('.').each do |path|
 if has_valid_ext
 exe = File.join(path, "#{cmd}")
 return File.absolute_path(exe) if File.file?(exe) and File.executable?(exe)
 end
 exts.each do |ext|
 exe = File.join(path, "#{cmd}#{ext}")
 return File.absolute_path(exe) if File.file?(exe) and File.executable?(exe)
 end
 end
 else
 paths.each do |path|
 exe = File.join(path, cmd)
 return File.absolute_path(exe) if File.file?(exe) and File.executable?(exe)
 end
 end
 end
 nil
end
</code></pre>

blocks|key|1137849|text|对于jruby，任何依赖于mkmf的解决方案都可能不起作用，因为它有一个C扩展。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1137850|对于jruby，以下是检查路径中是否有可执行内容的简单方法：|1137851|main+»+unix_process+=+java.lang.Runtime.getRuntime().exec("git+status")
=>+#<Java::JavaLang::UNIXProcess:0x64fa1a79>
main+»+unix_process.exitValue()
=>+0
main+»|code-block|syntax|javascript|1137852|如果可执行文件不在那里，它将引发运行时错误，因此在实际使用中，您可能希望在try/catch块中执行此操作。|1137853|entityMap^0|D|4|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|U|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|V|8|@]|D|@]|E|$]]|$1|O|3|-4|5|6|7|W|8|@]|D|@]|E|$]]]|P|$]]

for jruby, any of the solutions that depend on <code>mkmf</code> may not work, as it has a C extension.

for jruby, the following is an easy way to check if something is executable on the path:

<pre><code>main » unix_process = java.lang.Runtime.getRuntime().exec("git status")
=&gt; #&lt;Java::JavaLang::UNIXProcess:0x64fa1a79&gt;
main » unix_process.exitValue()
=&gt; 0
main »
</code></pre>

if the executable isn't there, it will raise a runtime error, so you may want to do this in a try/catch block in your actual usage.

blocks|key|1353118|text|#####################################################
#+add+methods+to+see+if+there's+an+executable+that's+executable
#####################################################
class+File
++class+<<+self
++++###########################################
++++#+exists+and+executable
++++###########################################
++++def+cmd_executable?(cmd)
++++++!ENV['PATH'].split(':').select+{+%7Cf%7C+executable?(join(f,+cmd[/%5E[%5E+\n\r]*/]))+}.empty?
++++end
++end
end|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1353119|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>#####################################################
# add methods to see if there's an executable that's executable
#####################################################
class File
 class &lt;&lt; self
 ###########################################
 # exists and executable
 ###########################################
 def cmd_executable?(cmd)
 !ENV['PATH'].split(':').select { |f| executable?(join(f, cmd[/^[^ \n\r]*/])) }.empty?
 end
 end
end
</code></pre>

blocks|key|1353145|text|我有这个：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1353146|def+command?(name)
++[name,
+++*ENV['PATH'].split(File::PATH_SEPARATOR).map+{%7Cp%7C+File.join(p,+name)}
++].find+{%7Cf%7C+File.executable?(f)}
end|code-block|syntax|javascript|1353147|适用于完整路径和命令：|1353148|irb(main):043:0>+command?("/bin/bash")
=>+"/bin/bash"
irb(main):044:0>+command?("bash")
=>+"/bin/bash"
irb(main):006:0>+command?("bush")
=>+nil|1353149|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

I have this:

<pre><code>def command?(name)
 [name,
 *ENV['PATH'].split(File::PATH_SEPARATOR).map {|p| File.join(p, name)}
 ].find {|f| File.executable?(f)}
end
</code></pre>

works for full paths as well as commands:

<pre><code>irb(main):043:0&gt; command?("/bin/bash")
=&gt; "/bin/bash"
irb(main):044:0&gt; command?("bash")
=&gt; "/bin/bash"
irb(main):006:0&gt; command?("bush")
=&gt; nil
</code></pre>

my scripts rely heavily on external programs and scripts.
I need to be sure that a program I need to call exists.
Manually, I'd check this using 'which' in the commandline.
Is there an equivalent to <code>File.exists?</code> for things in <code>$PATH</code>?
(yes I guess I could parse <code>%x[which scriptINeedToRun]</code> but that's not super elegant.
Thanks!
yannick
<hr />
UPDATE: Here's the solution I retained:
<pre><code> def command?(command)
 system(&quot;which #{ command} &gt; /dev/null 2&gt;&amp;1&quot;)
 end
</code></pre>
<hr />
<h3>UPDATE 2: A few new answers have come in - at least some of these offer better solutions.</h3>
<h3>Update 3: The <a href="https://github.com/djberg96/ptools" rel="noreferrer">ptools gem</a> has adds a &quot;which&quot; method to the File class.</h3>

"which in ruby": Checking if program exists in $PATH from ruby

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我的脚本很大程度上依赖于外部程序和脚本。我需要确保我需要调用的程序存在。手动地，我会在命令行中使用'which‘来检查它。在$PATH中有没有等同于File.exists?的东西(是的，我想我可以解析%x[which scriptINeedToRun]，但这并不是非常优雅。谢谢!yannick更新:以下是我保留的解决方...

问"which in ruby"：检查来自ruby的程序是否存在于$PATH中
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