BASH Shell使用变量中的空格扩展参数 [英] BASH shell expand arguments with spaces from variable

问题描述

说我有一个变量$ARGS，其中包含以下内容:

file1.txt "second file.txt" file3.txt

如何将$ARGS的内容作为参数传递给命令(例如说cat $ARGS)，将"second file.txt"视为一个参数，而不将其拆分为"second和file.txt"? >

理想情况下，我希望能够将参数完全存储在变量中(从文本文件中读取，但我认为不相关)将参数传递给任何命令.

谢谢！

解决方案

在不使用bash数组或eval的情况下可以做到这一点:这是xargs在不使用-0的情况下为数不多的行为之一或-d扩展名(通常会产生错误的行为)实际上很有用.

# this will print each argument on a different line
# ...note that it breaks with arguments containing literal newlines!
xargs printf '%s\n' <<<"$ARGS"

...或...

# this will emit arguments in a NUL-delimited stream
xargs printf '%s\0' <<<"$ARGS"

# in bash 4.4, you can read this into an array like so:
readarray -t -d '' args < <(xargs printf '%s\0' <<<"$ARGS")
yourprog "${args[@]}" # actually run your programs

# in bash 3.x or newer, it's just a bit longer:
args=( );
while IFS= read -r -d '' arg; do
    args+=( "$arg" )
done < <(xargs printf '%s\0' <<<"$ARGS")
yourprog "${args[@]}" # actually run your program

# in POSIX sh, you can't safely handle arguments with literal newlines
# ...but, barring that, can do it like this:
set --
while IFS= read -r arg; do
    set -- "$@" "$arg"
done < <(printf '%s\n' "$ARGS" | xargs printf '%s\n')
yourprog "$@" # actually run your program

...或者让xargs自己进行调用:

# this will call yourprog with ARGS given
# ...but -- beware! -- will cause bugs if there are more arguments than will fit on one
# ...command line invocation.
printf '%s\n' "$ARGS" | xargs yourprog

Say I have a variable $ARGS which contains the following:

file1.txt "second file.txt" file3.txt

How can I pass the contents of $ARGS as arguments to a command (say cat $ARGS, for example), treating "second file.txt" as one argument and not splitting it into "second and file.txt"?

Ideally, I'd like to be able to pass arguments to any command exactly as they are stored in a variable (read from a text file, but I don't think that's pertinent).

Thanks!

解决方案

It's possible to do this without either bash arrays or eval: This is one of the few places where the behavior of xargs without either -0 or -d extensions (a behavior which mostly creates bugs) is actually useful.

# this will print each argument on a different line
# ...note that it breaks with arguments containing literal newlines!
xargs printf '%s\n' <<<"$ARGS"

...or...

# this will emit arguments in a NUL-delimited stream
xargs printf '%s\0' <<<"$ARGS"

# in bash 4.4, you can read this into an array like so:
readarray -t -d '' args < <(xargs printf '%s\0' <<<"$ARGS")
yourprog "${args[@]}" # actually run your programs

# in bash 3.x or newer, it's just a bit longer:
args=( );
while IFS= read -r -d '' arg; do
    args+=( "$arg" )
done < <(xargs printf '%s\0' <<<"$ARGS")
yourprog "${args[@]}" # actually run your program

# in POSIX sh, you can't safely handle arguments with literal newlines
# ...but, barring that, can do it like this:
set --
while IFS= read -r arg; do
    set -- "$@" "$arg"
done < <(printf '%s\n' "$ARGS" | xargs printf '%s\n')
yourprog "$@" # actually run your program

...or, letting xargs itself do the invocation:

# this will call yourprog with ARGS given
# ...but -- beware! -- will cause bugs if there are more arguments than will fit on one
# ...command line invocation.
printf '%s\n' "$ARGS" | xargs yourprog

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