sed script fails to run in dash
Hi,
I am puzzled and don't know why this command does not work with dash (I am currently using the debian stable (v7.2) version of dash (v0.5.7-3)):
echo 1>/tmp/x; reponse=$( sed -e $(wc -l </tmp/x)$'{w/dev/stdout\n;d}' -i /tmp/x ); echo "reponse='$reponse'"
but also just this line:
sed -e 1$'{w/dev/stdout\n;d}' -i /tmp/xin a dash script will yield the error message:
sed: -e expression #1, char 2: unknown command: `$'
But why ? :(
I would be really grateful for any explanation.
Thanks a lot in advance for any hint!
Tormen
P.S.: The source for the above line is:
http://stackoverflow.com/questions/13804967/bash-pop-lines-in-a-file
Le Fri, 22 Nov 2013 19:11:42 +0100
Tormen a écrit:
Hello,
Quoted 9 lines
but also just this line:
sed -e 1$'{w/dev/stdout\n;d}' -i /tmp/xin a dash script will yield the error message:
sed: -e expression #1, char 2: unknown command: `$'
But why ? :(
It seems dash strictly passes what you have given and which is sed-speaking incorrect:
$ dash -c "strace sed -e 1$'{w/dev/stdout\n;d}' -i /tmp/x"
execve("/usr/bin/sed", ["sed", "-e", "1${w/dev/stdout\\n;d}", ...
^^^
Bash does not, and so passes something sed understands:$ bash -c "strace sed -e 1$'{w/dev/stdout\n;d}' -i /tmp/x"
execve("/usr/bin/sed", ["sed", "-e", "1{w/dev/stdout \n;d}", ...
^^^
If you escape the "$" with bash, you will get your kitten back:$ bash -c "sed -e 1\\$'{w/dev/stdout\n;d}' -i /tmp/x"
sed: -e expression #1, char 2: unknown command: `$'Take care,
Seb.
Hi Tormen,
Quoted 7 lines · Tormen
sed -e 1$'{w/dev/stdout\n;d}' -i /tmp/xin a dash script will yield the error message:
sed: -e expression #1, char 2: unknown command: `$'
But why ? :(
POSIX sayeth[1]:
The '$' character is used to introduce parameter expansion, command substitution, or arithmetic evaluation. If an unquoted '$' is followed by a character that is not one of the following:
* A numeric character
* The name of one of the special parameters (see 2.5.2 Special Parameters)
* A valid first character of a variable name
* A <left-curly-bracket> ( '{' )
* A <left-parenthesis>
the result is unspecified.
A single-quote is not the name of a special parameter nor valid as the first character of a variable name, so this is unspecified behavior and should be avoided in scripts meant to run on an arbitrary POSIX shell.
However the next major version of POSIX is likely to mandate support for $'' string handling[2]. Work towards an implementation in dash would be very welcome.
Thanks and hope that helps,
Jonathan
[1] http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06
[2] http://austingroupbugs.net/view.php?id=249
Quoted 7 lines · Tormen
sed -e 1$'{w/dev/stdout\n;d}' -i /tmp/xin a dash script will yield the error message:
sed: -e expression #1, char 2: unknown command: `$'
But why ? :(
Because $'' is not (yet) in POSIX. It will be required in a future release, but dash hasn't implemented it yet.
http://austingroupbugs.net/view.php?id=249
Signature · 2 lines
Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
Quoted 6 lines · Eric Blake
Quoted 4 lines · Tormen
sed -e 1$'{w/dev/stdout\n;d}' -i /tmp/xin a dash script will yield the error message:
Quoted 7 lines
Quoted 3 lines
sed: -e expression #1, char 2: unknown command: `$'
But why ? :(
Because $'' is not (yet) in POSIX. It will be required in a future release, but dash hasn't implemented it yet.
Now I get how this script works ;)
Thanks !! :)
!!! And also thanks to all the other answers !!! - really appreciated! :)))