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Re: Bash heredoc on FD 3




On Tue, 4 Dec 2018 09:21:55, cyg Simple  wrote:

> Dash is faster in processing the data but can be made to fail if you
> add -d to the ls commands you're using. 

?

Oh, I believe you refer to:

    https://cygwin.com/ml/cygwin/2018-12/msg00035.html
    ( Re: Bash heredoc on FD 3 )

> So in Bash the process is no longer available.  Adding -d to the above:
> 
> $ dash -c '/bin/ls -ld /dev/fd/*'
> /bin/ls: cannot access '/dev/fd/3': No such file or directory
> lrwxrwxrwx 1 eboyd53 eboyd53 0 Dec  3 10:50 /dev/fd/0 -> /dev/pty2
> lrwxrwxrwx 1 eboyd53 eboyd53 0 Dec  3 10:50 /dev/fd/1 -> /dev/pty2
> lrwxrwxrwx 1 eboyd53 eboyd53 0 Dec  3 10:50 /dev/fd/2 -> /dev/pty2

uhm, the facts are slightly different ...

/dev/fd is, well, a "moving target", it is symlnk to /proc/self/fd.

self refers to the "current process" ... it changes each time.

/proc/self/fd shows the open fd's of the current process ...

Currently, I am on Linux (Fedora) ...

@@ # currently I am executing the shell (bash)
@@ # self points to the procid of my bash ...

@@ printf "%s\n" /dev/fd/*
/dev/fd/0
/dev/fd/1
/dev/fd/10
/dev/fd/11
/dev/fd/2
/dev/fd/255
/dev/fd/3

@@ # however ls has NO open fd 3 if I invoke it like this:
@@ # (self points to the procid of my ls command)

@@ ls -ld /dev/fd/* # /dev/fd/* expands to the list above (bash)
ls: cannot access '/dev/fd/255': No such file or directory
ls: cannot access '/dev/fd/3': No such file or directory
lrwx------ 1 henri henri 64 Dec  5 07:26 /dev/fd/0 -> /dev/pts/0
lrwx------ 1 henri henri 64 Dec  5 07:26 /dev/fd/1 -> /dev/pts/0
lrwx------ 1 henri henri 64 Dec  5 07:26 /dev/fd/10 -> /dev/dri/card0
lrwx------ 1 henri henri 64 Dec  5 07:26 /dev/fd/11 -> /dev/dri/card0
lrwx------ 1 henri henri 64 Dec  5 07:26 /dev/fd/2 -> /dev/pts/0

@@ # ls HAS an open fd 3 if I invoke it like this:
@@ (# use strace to see it happen -- ls opens the directory)

@@ ls -lL /dev/fd # /dev/fd refers to /proc/self/fd
total 0
crw-------  1 henri tty   136, 0 Dec  5 07:38 0
crw-------  1 henri tty   136, 0 Dec  5 07:38 1
crw-rw----+ 1 root  video 226, 0 Dec  5 07:01 10
crw-rw----+ 1 root  video 226, 0 Dec  5 07:01 11
crw-------  1 henri tty   136, 0 Dec  5 07:38 2
dr-x------  2 henri henri      0 Dec  5 07:38 3
@@ ls -l /proc/self/fd
total 0
lrwx------ 1 henri henri 64 Dec  5 07:38 0 -> /dev/pts/0
lrwx------ 1 henri henri 64 Dec  5 07:38 1 -> /dev/pts/0
lrwx------ 1 henri henri 64 Dec  5 07:38 10 -> /dev/dri/card0
lrwx------ 1 henri henri 64 Dec  5 07:38 11 -> /dev/dri/card0
lrwx------ 1 henri henri 64 Dec  5 07:38 2 -> /dev/pts/0
lr-x------ 1 henri henri 64 Dec  5 07:38 3 -> /proc/2605/fd

Same w/ dash:

@@ dash
$ printf "%s\n" /dev/fd/*
/dev/fd/0
/dev/fd/1
/dev/fd/10
/dev/fd/11
/dev/fd/12
/dev/fd/17
/dev/fd/18
/dev/fd/2
/dev/fd/3
/dev/fd/55
$ ls -ld /dev/fd/*
ls: cannot access '/dev/fd/12': No such file or directory
ls: cannot access '/dev/fd/3': No such file or directory
lrwx------ 1 henri henri 64 Dec  5 07:25 /dev/fd/0 -> /dev/pts/3
lrwx------ 1 henri henri 64 Dec  5 07:25 /dev/fd/1 -> /dev/pts/3
lrwx------ 1 henri henri 64 Dec  5 07:25 /dev/fd/10 -> /dev/dri/card0
lrwx------ 1 henri henri 64 Dec  5 07:25 /dev/fd/11 -> /dev/dri/card0
lrwx------ 1 henri henri 64 Dec  5 07:25 /dev/fd/17 -> /dev/dri/card0
lrwx------ 1 henri henri 64 Dec  5 07:25 /dev/fd/18 -> /dev/dri/card0
lrwx------ 1 henri henri 64 Dec  5 07:25 /dev/fd/2 -> /dev/pts/3
lr-x------ 1 henri henri 64 Dec  5 07:25 /dev/fd/55 -> /home/b/henri/.local/share/baloo/index

=====


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