Question

假设我们有这个简单的脚本（selfie.sh）：

echo "$0"

我怎么判断它是否以这种方式执行sh selfie.sh，例如cat selfie.sh | sh？

sh selfie.sh给出这个：

selfie.sh

和cat selfie.sh | sh输出：

sh

我的尝试：

[ -s "$0" ]

pwd无法提供帮助
$BASH_SOURCE或类似内容与 POSIX shell

这个问题摆在我面前，因为我写了一个名为shell-utils的项目，我希望用户可以像这样安装第一次安装：

curl -L https://raw.githubusercontent.com/oxnz/shell-utils/master/tool/install | sh

但如果（s）他已经拥有该软件的副本并从他的shell中调用如下：

sh shell-utils/tool/install.sh

我需要区分并采取不同的行动。

Answer 1

尝试-t条件表达式。

$ cat selfie.sh
[ -t 0 ] && echo "bash is reading a script from somewhere else" || echo "bash is reading a script from stdin"
$ cat selfie.sh | sh
bash is reading a script from stdin
$ sh selfie.sh
bash is reading a script from somewhere else

Answer 2

您可以使用以下符合POSIX标准的shell函数。

唯一的先决条件是Unix平台，其中stdin表示为文件/dev/stdin，现在通常就是这种情况。

你只会在一个非常不寻常的情况下得到误报：如果，当 sourcing 一个脚本时，你也提供管道输入;例如，echo hi | . selfie.sh

#!/bin/sh

# Indicates via exit code whether the contents of the script at hand
# were provided through a pipe, e.g., `curl .... | sh`.
# Caveat: You'll get a false positive in the following - exotic - corner case:
#         ... | . script # combination of pipeline input and sourcing.
isThisScriptPiped() {
  if [ ! -f "$0" ] || [ -x "$0" ] && POSIXLY_CORRECT=1 file -- "$0" | grep -Fvq 'text'; then
    if POSIXLY_CORRECT=1 file -i /dev/stdin | grep -Fq 'fifo'; then
      return 0
    fi
  fi
  return 1
}

# Sample call
isThisScriptPiped && echo 'PIPED' || echo 'NOT piped'

以下是相同功能的带注释的版本：

#!/bin/sh

# Note: POSIXLY_CORRECT is set below to make the GNU `file` utility behave
#       in a POSIX-compliant manner so as to report the type of the *target*
#       in the event that the operand is a *symlink*.
#       This *could* happen with a shell executable that is a symlink, and 
#       *definitely* happens with /dev/stdin, which on Linux is a symlink to
#       /proc/self/fd/0.

# Indicates via exit code whether the contents of the script at hand
# were provided through a pipe, e.g., `curl .... | sh`.
# Caveat: You'll get a false positive in the following - exotic - corner case:
#         ... | . script # combination of pipeline input and sourcing.
isThisScriptPiped() {

  # Test 1 of 2: Check if $0 refers to:
  #  either: a nonexisting file (implies that $0 refers to an executable in
  #          the path)
  #  or: an executable file that is not text-based (not a shell script)
  # Both cases imply that $0 refers to a shell executable, which in turn implies
  # that no filename argument (script file path) was passed to the shell.
  # Note that while `file` implementations differ, their output for text-based
  # executables (shell scripts) always contains 'text' (POSIX mandates
  # 'commands text', but neither BSD nor GNU `file` do that).
  if [ ! -f "$0" ] || [ -x "$0" ] && POSIXLY_CORRECT=1 file -- "$0" | grep -Fvq 'text'; then

    # The implication is that the script contents comes from:
    #  - either: stdin - whether through input redirection (sh < script) or
    #            from a pipe (... | sh)
    #  - or: from sourcing (. script)
    # Note that in sh there is no way that I know of that lets you determine
    # reliably whether the script is being sourced. Knowing whether the script
    # is being sourced *or* provided via stdin is as close as you can get.
    # (To check for sourcing in Bash, Ksh, or Zsh, see 
    #  http://stackoverflow.com/a/28776166/45375 )

    # Test 2 of 2:
    #  See if stdin is connected to a pipe, which in combination with test 1
    #  implies that the script contents is being piped, EXCEPT in one scenario:
    #  Caveat: You'll get a false positive in the following - very unusual - 
    #          corner case:
    #            ... | . script # combination of sourcing and pipe input
    #  Note:
    #    - POSIX mandates that when passing a FIFO (named pipe) to `file`
    #      the output contain the string 'fifo', which is true of both BSD
    #      and GNU `file`.
    #    - Option -i is crucial to prevent `file` from trying to
    #      read the *contents* of stdin; with -i, it just reports the basic
    #      file type.
    if POSIXLY_CORRECT=1 file -i /dev/stdin | grep -Fq 'fifo'; then
      return 0
    fi

  fi

  return 1

}

# Sample call
isThisScriptPiped && echo 'PIPED' || echo 'NOT piped'

如何判断是否从管道执行脚本？

2 个答案: