检查文件是否存在包含空格的文件名 [英] Check if a file exists with a filename containing spaces

问题描述

我正在Bash中测试文件是否存在，文件名使用$(printf '%q' "$FNAME")进行转义.

I am testing in Bash for if a file is existing, where the file name is escaped using $(printf '%q' "$FNAME").

这总是使用if [ -f $FNAME ]产生错误，如下面的注释示例所示.如何测试包含空格和其他字符的文件名?

This always produces an error using if [ -f $FNAME ] as in the commented example below. How can I test for a filename that contains spaces and other characters?

#!/usr/bin/env bash

# code used in Raspberry Pi Podcasting Jukebox project
# youtube-dl -f 17 --get-filename https://www.youtube.com/watch?v=AgkM5g_Ob-w
# returns "HOW ABUNDANCE WILL CHANGE THE WORLD - Elon Musk 2017-AgkM5g_Ob-w.3gp"

# Purpose: To test if file exists before downloading
# for testing purposes using an existing regular file "abc def ghi"
AFILE="abc def ghi"
TFILE=$(printf '%q' "$AFILE") # Escaping filename using printf
echo $TFILE # returns abc\ def\ ghi
# if [ -f $AFILE ] # this test returns false every time with error [:too many arguments

if [ -f $TFILE ] # This test also returns FALSE with err [: too many arguments
then
  echo "Existing"
  # don't download
else
  echo "Not existing"
  # youtube-dl http://www.youtube.com/watch?v=AgkM5g_Ob-w
fi

推荐答案

总是引用您的文件名，使用%q来转义空格的想法是正确的，但是与[运算符一起使用时，未引用的$TFILE拆分为多个单词，导致-f操作数在实际上期望单个参数时接收太多参数.因此，一旦将其双引号括起来，就会保留空格，并在条件中传递一个字面量的单个参数.

Always quote your file-name, the idea of using %q for escaping the spaces is right, but when used with the [ operator the unquoted $TFILE is split into multiple words causing the -f operand to receive too many arguments when it was actually expecting a single argument. So once you double-quote it, the white-spaces are preserved and a literal single argument is passed in the conditional.

testFile="abc def ghi"
printf -v quotedFile '%q' "$testFile"

if [ -f "$quotedFile" ]; then
    printf 'My quoted file %s exists\n' "$quotedFile"
fi

以上内容在任何POSIX兼容shell中都应适用([的用法).但是，如果仅针对bash shell的脚本目标，则可以使用[[，其中不再需要使用引号，因为它将其作为表达式进行评估.所以你可以做

the above should apply well (the usage of [) in any POSIX compatible shells. But if you are targeting scripts for bash shell alone, you can use the [[ in which quoting is never necessary as it evaluated as an expression. So you can just do

file_with_spaces="abc def ghi"
if [[ -f $file_with_spaces ]]; then
    printf 'My quoted file %s exists\n' "$file_with_spaces"
fi

但是一般来说，在bash中的变量中添加引号不会有什么坏处.您随时可以做到.

But in general it doesn't hurt to add quotes to variables in bash. You can always do it.

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