Bash Reference Mamual
Hi, In section 3.5.4 "Command Substitution", the following sentence may have a typo: > The command substitution $(cat file) can be replaced by the equivalent but > faster $(< file). My proposed change: > The command substitution $(cat file) can be replaced by the equivalent but > faster <(cat file). If the manual is correct and I misunderstood something, please let me know. Thanks, Craig -- Craig H Maynard 103 North Road Wakefield, RI 02879 (401) 413-2376
Re: Bash Reference Mamual
On Sat, Oct 17, 2020 at 3:48 PM Craig H Maynard wrote:
> Hi,
>
> In section 3.5.4 "Command Substitution", the following sentence may have a
> typo:
>
> > The command substitution $(cat file) can be replaced by the equivalent
> but faster $(< file).
>
>
> My proposed change:
>
> > The command substitution $(cat file) can be replaced by the equivalent
> but faster <(cat file).
>
>
> If the manual is correct and I misunderstood something, please let me know.
>
Hi Craig,
<(cat file) and $(cat file) are not equivalent constructs. The former will
expand to a file name (e.g. "/dev/fd/63"), whereas the latter will expand
to the contents of the file.
In the case of $(cat file) and $(< file), they are equivalent, except
that in the second case there's no external command ("cat"), and instead
Bash reads the file and does the expansion itself.
Re: Bash Reference Mamual
> On Oct 17, 2020, at 7:35 PM, Eduardo Bustamante wrote: > > <(cat file) and $(cat file) are not equivalent constructs. The former will > expand to a file name (e.g. "/dev/fd/63"), whereas the latter will expand > to the contents of the file. If you want terms you can look up, $(cat file) and $(< file) are *command substitutions*, while <(cat file) is a *process substitution*. $ printf 'FILE CONTENTS' >tmp $ printf '|%s|\n' "$(cat tmp)" |FILE CONTENTS| $ printf '|%s|\n' "$(< tmp)" |FILE CONTENTS| $ printf '|%s|\n' "<(cat tmp)" |<(cat tmp)| $ printf '|%s|\n' <(cat tmp) |/dev/fd/63| -- vq
