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检查是否没有命令行参数且 STDIN 为空

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检查是否没有命令行参数且 STDIN 为空

如何在 Bash 脚本中检查是否未提供命令行参数或 STDIN？

我的意思是如果我跑：

#> ./myscript.sh
... Show message "No data provided..." and exit

或者：

#> ./myscript.sh filename.txt
... Read from filename.txt

或者：

#> ./myscript.sh < filename.txt**
... Read from STDIN

答案1

这符合您的要求吗？

#!/bin/sh

if test -n "$1"; then
    echo "Read from $1";
elif test ! -t 0; then
    echo "Read from stdin"
else
    echo "No data provided..."
fi

主要技巧如下：

  • 检测是否有参数是通过test -n $1检查第一个参数是否存在来完成的。

  • 然后，检查stdin终端上是否未打开（因为它通过管道传输到文件）test ! -t 0（检查文件描述符零（又名stdin）是否未打开）。

  • 最后，其他所有情况都属于最后一种情况 ( No data provided...)。

答案2

我四处寻找却无果，最后经过反复尝试终于成功将其整合在一起。自此以后，它已在众多用例中完美地发挥作用。

#!/bin/bash
### LayinPipe.sh
## Recreate "${@}" as "${Args[@]}"; appending piped input.
## Offers usable positional parameters regardless of where the input came from.
##
## You could choose to create the array with "${@}" instead following
##  any piped arguments by simply swapping the order
##   of the following two 'if' statements.

# First, check for normal positional parameters.
if [[ ${@} ]]; then
    while read line; do
        Args[${#Args[@]}]="${line}"
    done < <(printf '%s\n' "${@}")
fi

# Then, check for piped input.
if [[ ! -t 0 ]]; then
    while read line; do
        Args[${#Args[@]}]="${line}"
    done < <(cat -)
fi

# Behold the glory.
for ((a=0;a<${#Args[@]};a++)); do
    echo "${a}: ${Args[a]}"
done
  • 示例：（充分了解不鼓励使用“ls”的输出作为输入，以显示此解决方案的灵活性。）
$ ls
: TestFile.txt 'Filename with spaces'

$ ls -1 | LayinPipe.sh "$(ls -1)"
> 0: Filename with spaces
> 1: TestFile.txt 
> 2: Filename with spaces
> 3: TestFile.txt 

$ LayinPipe.sh "$(ls -1)"
> 0: Filename with spaces
> 1: TestFile.txt 

$ ls -1 | LayinPipe.sh
> 0: Filename with spaces
> 1: TestFile.txt

答案3

[已解决] 在 bash shell 中...

... read -t 0 ：参见“帮助阅读”

$ function read_if_stdin_not_empty {
if read -t 0 ; then
  while read ; do
    echo "stdin receive : $REPLY"
    read_if_stdin_not_empty
  done
else 
  echo "stdin is empty .."
fi
}

# TESTs:

$ read_if_stdin_not_empty
stdin is empty ..

$ echo '123' | read_if_stdin_not_empty
stdin receive : 123

$s='123                        
456'
$ echo "$s" | read_if_stdin_not_empty
stdin receive : 123
stdin receive : 456

答案4

我提出了一个综合了之前非常有趣的答案的函数：

文件test.sh：

#!/bin/bash
function init_STDIN() {
  ## Version 1.0.0
  ## Creates the global variable array indexed STDIN
  ## which contains the possible lines sent in the
  ## file descriptor /dev/stdin of the script
  declare -ga STDIN
  read -t0 || return 1
  while read LINE; do
    STDIN[${#STDIN[@]}]="$LINE"
  done < <(cat -)
  test ${#STDIN[@]} -ne 0
}

if init_STDIN; then
  echo "Feed provided on /dev/stdin. Processing..."
  echo "For this example, /dev/stdin is:"
  for ((I=0; I<${#STDIN[@]}; I++)); do
    echo ${STDIN[$I]}
  done
else
  echo "Working without any feed on /dev/stdin..."
fi

echo
echo "For this example, the ${#@} parameter(s) provided on the command line is(are) :"
echo $@

测试：

$ ./test.sh some args ...
Working without any feed on /dev/stdin...

For this example, the 3 parameter(s) provided on the command line is(are) :
some args ...


$ seq 1 10 | sed 's/ /\n/g' | ./test.sh some args ...
Feed provided on /dev/stdin. Processing...
For this example, /dev/stdin is:
1
2
3
4
5
6
7
8
9
10

For this example, the 3 parameter(s) provided on the command line is(are) :
some args ...


$ seq 1 10 | sed 's/ /\n/g' | (exec 0<&-; ./test.sh some args ...)
Working without any feed on /dev/stdin...

For this example, the 3 parameter(s) provided on the command line is(are) :
some args ...

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