下面的Perl脚本(my.pl)既可以从命令行参数中的文件读取,也可以从标准输入(STDIN)读取:

while (<>) {
   print($_);
}

Perl my.pl将从标准输入中读取,而Perl my.pl .txt将从a.txt中读取。这很方便。

Bash中也有类似的功能吗?


当前回答

Use:

for line in `cat`; do
    something($line);
done

其他回答

请尝试以下代码:

while IFS= read -r line; do
    echo "$line"
done < file

这是最简单的方法:

#!/bin/sh
cat -

用法:

$ echo test | sh my_script.sh
test

要将stdin分配给变量,您可以使用:stdin =$(cat -)或只是简单的stdin =$(cat)作为操作符是不必要的(根据@mklement0注释)。


要解析标准输入中的每一行,请尝试以下脚本:

#!/bin/bash
while IFS= read -r line; do
  printf '%s\n' "$line"
done

要从文件或stdin中读取(如果参数不存在),您可以将其扩展为:

#!/bin/bash
file=${1--} # POSIX-compliant; ${1:--} can be used either.
while IFS= read -r line; do
  printf '%s\n' "$line" # Or: env POSIXLY_CORRECT=1 echo "$line"
done < <(cat -- "$file")

Notes: - read -r - Do not treat a backslash character in any special way. Consider each backslash to be part of the input line. - Without setting IFS, by default the sequences of Space and Tab at the beginning and end of the lines are ignored (trimmed). - Use printf instead of echo to avoid printing empty lines when the line consists of a single -e, -n or -E. However there is a workaround by using env POSIXLY_CORRECT=1 echo "$line" which executes your external GNU echo which supports it. See: How do I echo "-e"?

参见:当没有参数传递时如何读取stdin ?在stackoverflow SE

以下是使用标准sh(在Debian上用Dash测试)的工作,相当可读,但这是一个品味问题:

if [ -n "$1" ]; then
    cat "$1"
else
    cat
fi | commands_and_transformations

详细信息:如果第一个参数非空,则cat该文件,否则cat标准输入。然后整个if语句的输出由command_and_transforms处理。

Use:

for line in `cat`; do
    something($line);
done

与…

while read line
do
    echo "$line"
done < "${1:-/dev/stdin}"

我得到以下输出:

忽略标准输入中的1265个字符。使用“-stdin”或“-”来说明如何处理管道输入。

然后决定用for:

Lnl=$(cat file.txt | wc -l)
echo "Last line: $Lnl"
nl=1

for num in `seq $nl +1 $Lnl`;
do
    echo "Number line: $nl"
    line=$(cat file.txt | head -n $nl | tail -n 1)
    echo "Read line: $line"
    nl=$[$nl+1]
done