I am following https://docs.docker.com/get-started/06_bind_mounts/#start-a-dev-mode-container on a Windows PC and am stuck here:
Run the following command. We’ll explain what’s going on afterwards:
docker run -dp 3000:3000 \
-w /app -v "$(pwd):/app" \
node:12-alpine \
sh -c "yarn install && yarn run dev"
If you are using PowerShell then use this command:
docker run -dp 3000:3000 `
-w /app -v "$(pwd):/app" `
node:12-alpine `
sh -c "yarn install && yarn run dev"
When using Command Prompt, I get errors (tried multiple variations as shown below), and when using PowerShell, I don't appear to get errors but am not running anything as showed when executing docker ps.
Note that I would rather use Command Prompt and not PowerShell as I could use Linux commands with ComandPrompt on my PC.
What is the significance of backslashes when using Dockers with Command Prompt (and tick marks with PowerShell for that matter)?
I have since found that docker run -dp 3000:3000 -w /app -v "%cd%:/app" node:12-alpine sh -c "yarn install && yarn run dev" works without errors (got rid of backslashes, put on one line, and used %cd% instead of $(pwd)), but would still like to know why using the exact script in the example results in errors.
Using Command Prompt
C:\Users\michael\Documents\Docker\app>docker run -dp 3000:3000 \
docker: invalid reference format.
See 'docker run --help'.
C:\Users\michael\Documents\Docker\app> -w /app -v "$(pwd):/app" \
'-w' is not recognized as an internal or external command,
operable program or batch file.
C:\Users\michael\Documents\Docker\app> node:12-alpine \
The filename, directory name, or volume label syntax is incorrect.
C:\Users\michael\Documents\Docker\app> sh -c "yarn install && yarn run dev"
sh: yarn: command not found
C:\Users\michael\Documents\Docker\app>docker run -dp 3000:3000 \ -w /app -v "$(pwd):/app" \ node:12-alpine \ sh -c "yarn install && yarn run dev"
docker: invalid reference format.
See 'docker run --help'.
C:\Users\michael\Documents\Docker\app>docker run -dp 3000:3000 -w /app -v "$(pwd):/app" node:12-alpine sh -c "yarn install && yarn run dev"
docker: Error response from daemon: create $(pwd): "$(pwd)" includes invalid characters for a local volume name, only "[a-zA-Z0-9][a-zA-Z0-9_.-]" are allowed. If you intended to pass a host directory, use absolute path.
See 'docker run --help'.
C:\Users\michael\Documents\Docker\app>
Using PowerShell
PS C:\Users\michael\Documents\Docker> docker run -dp 3000:3000 `
>> -w /app -v "$(pwd):/app" `
>> node:12-alpine `
>> sh -c "yarn install && yarn run dev"
849af42e78d4ab09242fdd6c3d03bcf1b6b58de984c4485a441a2e2c88603767
PS C:\Users\michael\Documents\Docker> docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
PS C:\Users\michael\Documents\Docker>
would still like to know why using the exact script in the example results in errors.
Because the command with the line-ending \ characters is meant for POSIX-compatible shells such as bash, not for cmd.exe
POSIX-compatible shells (sh, bash, dash, ksh, zsh):
use \ for line-continuation (continuing a command on the following line) and escaping in general.
use $varName to reference both environment and shell-only variables.
support $(...) for embedding the output from a command (...) in command lines (command substitution).
support both double-quoted ("...", interpolating) and single-quoted ('...', verbatim) strings; use '\'' to - in effect - include a ' inside '...'.
(Additionally, in bash, ksh, and zsh, there are the rarely used ANSI C-quoted strings, $'...', and, in bash and ksh, perhaps even more rarely, localizable strings, $"...").
cmd.exe:
uses ^ for line-continuation and escaping in general (in unquoted arguments only).
uses %varName% to reference environment variables (the only variable type supported).
doesn't support command substitutions at all.
supports only "..." strings (interpolating).
PowerShell:
uses ` (the backtick) for line-continuation and escaping in general.
uses $env:varName to reference environment variables, $varName to reference shell-only variables.
supports $(...), called subexpressions, the equivalent of command substitutions (outside of double-quoted strings, (...) is usually sufficient).
supports both double-quoted ("...", interpolating) and single-quoted ('...', verbatim) strings; use '' to embed a ' inside '...'.
Note: A common pitfall is that PowerShell has more metacharacters compared to both POSIX-compatible shells and cmd.exe, notably including # { } , ;, which therefore require individual `-escaping in unquoted arguments or embedding in quoted strings - see this answer.
Potential line-continuation pitfall: in all of the shells discussed, the escape character must be the very last character on the line - not even trailing (intra-line) whitespace is allowed (because the escape character would then apply to it rather than to the newline).
The information above is summarized in the following table:
Feature
POSIX shells _
cmd.exe _
PowerShell _
Line-continuation / escape character
Backslash (\)
Caret (^)
Backtick (`)
Double-quoted strings (interpolating)
✅
✅
✅
Single-quoted strings (verbatim)
✅
❌
✅
Get / set environment variables
$varName /export varName=...
%varName% /set varName=...
$env:varName /$env:varName = ...
Get / set shell-only variables
$varName/varName=...
❌ (no such variables exist, but you can limit the scope of env. vars. with setlocal)
$varName/$varName = ...
Command substitutions, subexpressions
$(...)
❌
(...) / $(...), esp. in strings
Note re setting variables with respect to whitespace on either side of the = symbol:
In POSIX-like shells, there must not be whitespace around =.
In cmd.exe, such whitespace is significant and becomes part of the variable / value name, and is therefore usually to be avoided.
In PowerShell, such whitespace is optional - you may use it to enhance readability; any string value to be assigned requires quoting (e.g., $var = 'hi!')
See also:
https://hyperpolyglot.org/shell for a much more comprehensive juxtaposition of these shells, though note that - as of this writing - the information about PowerShell is incomplete.
Sage Pourpre's helpful answer for links to the line-continuation documentation of the respective shells.
This is character escaping.
The X Character (\ for Bash, backtick for Powershell and ^ for Windows terminal )are used to remove any specific meanings to the next characters.
When used at the end of a line, this mean that the next character (The newline character) is completely ignored.
This keep the command essentially a one-line command from the point of view of the interpreter, but allow you to break it on multiple lines for better readability.
References
Powershell - About special characters
Escape sequences begin with the backtick character [`], known as the grave
accent (ASCII 96), and are case-sensitive. The backtick character can
also be referred to as the escape character.
Bash manual
3.1.2.1 Escape Character
A non-quoted backslash \ is the Bash escape character. It preserves the literal value of the next character that
follows, with the exception of newline. If a \newline pair appears,
and the backslash itself is not quoted, the \newline is treated as a
line continuation (that is, it is removed from the input stream and
effectively ignored).
How-to: Escape Characters, Delimiters and Quotes at the Windows command line
Escaping CR/LF line endings. The ^ escape character can be used to
make long commands more readable by splitting them into multiple lines
and escaping the Carriage Return + Line Feed (CR/LF) at the end of a
line:
ROBOCOPY \\FileServ1\e$\users ^ \\FileServ2\e$\BackupUsers ^ /COPYALL /B /SEC /MIR ^ /R:0 /W:0 /LOG:MyLogfile.txt /NFL /NDL
[...]
A couple of things to be aware of:
A stray space at the end of a line (after the ^) will break the
command, this can be hard to spot unless you have a text editor that
displays spaces and tab characters. If you want comment something out
with REM, then EVERY line needs to be prefixed with REM. Alternatively
if you use a double colon :: as a REM comment, that will still parse
the caret at the end of a line, so in the example above changing the
first line to :: ROBOCOPY… will comment out the whole multi-line
command.
I need to SFTP a file to a server. The password has a dollar sign $ and I need to escape it.
I tried with Perl and sed commands I am able to replace but the string following $ is not getting added.
Example:
echo "Np4$g" | perl -pe 's/$/\\\\\$/g'
output
Np4\\$
It supposed to be Np4\\$g, but g is not getting appended.
Code:
/usr/bin/expect <<EOF
set timeout -1
spawn sftp -C -oPort=$port $sftp_username#$host_name
expect "password:"
send "$password\r"
expect "sftp>"
cd $remote_dir
send "mput *.txt\r"
expect "sftp>"
send
Your command
echo "Np4$g" | perl -pe 's/$/\\\\\$/g'
is failing for two reasons
In "Np4$g", the shell is interpolating the variable g into the double-quoted string. It probably isn't defined so it is replaced with nothing, and you are passing just Np4 to perl. You need to use single quotes to prevent the interpolation
In the Perl substitution s/$/\\\\\$/g the $ in the pattern matches the end of the string, not a literal dollar. That means Np4 is changed to Np4\\$. You need to escape the dollar sign in the pattern to get it to match a literal $
This will work correctly
echo 'Np4$g' | perl -pe 's/\$/\\\$/g'
output
Np4\$g
I suggest to not escape and replace
"Np4$g"
by
'Np4$g'
I am trying to put below command in perl system() function.But getting so many compilation errors (syntax).
./istool export -domain serviceshost:9080 -u dsadm -p password -ar test.isx -pre -ds '-base="ENGINEHOST/Dev_Project" Jobs/Batch/\*.*'
I was using it like in perl:
system("./istool export -domain serviceshost:9080 -u dsadm -p password -ar test.isx -pre -ds '-base="ENGINEHOST/Dev_Project" Jobs/Batch/\*.*'");
can some one guide me exactly how to use it in system function?I tried escaping . also with backslash(\) in front of it.
Replace system with print, and it's obvious you didn't build the string correctly.
If you want to include a " in a string quoted with ", you need to escape it.
If you want to include a \ in a double-quoted string, you need to escape it.
I want to run shell command as follow in perl:
tar --exclude="*/node_modules" \
--exclude="*/vendor" \
--exclude='.git' \
-zvcf /tmp/robot.tgz .
But it seems perl can not excute this:
`tar --exclude="cv/node_modules" \
--exclude="*/vendor" \
--exclude='.git' \
-zvcf /tmp/robot.tgz .`;
Here is the error:
tar: Must specify one of -c, -r, -t, -u, -x
sh: line 1: --exclude=*/vendor: No such file or directory
sh: line 2: --exclude=.git: command not found
sh: line 3: -zvcf: command not found
it seems perl treat each line as one command.
Update
I apologise. My original diagnosis was wrong
It is hard to clearly express in a post like this the contents of strings that contain Perl escape characters. If anything below is unclear to you then please write a comment to say so. I hope I haven't made things unnecessarily complicated
My original solution below is still valid, and will give you better control over the contents of the command, but my reasons for why the OP's code doesn't work for them were wrong, and the truth offers other resolutions
The problem is that the contents of backticks (or qx/.../) are evaluated as a double-quoted string, which means that Perl variables and escape sequences like \t and \x20 are expanded before the string is executed. One of the consequences of this is that a backslash is deleted if it is followed by a literal newline, leaving just the newline
That means that a statement like this
my $output = `ls \
-l`;
will be preprocessed to "ls \n-l" and will no longer contain the backslash that is needed to signal to the shell that the newline should be removed (or indeed to get the command passed to the shell in the first place)
Apart from manipulating the command string directly as I described in my original post below, there are two solutions to this. The first is to escape the backslash itself by doubling it up, like this
my $output = `ls \\
-l`;
which will prevent it from being removed by Perl. That will pass the backslash-newline sequence to the shell, which will remove it as normal
The other is to use qx'...' instead of backticks together with single-quote delimiters, which will prevent the contents from being processed as a double-quoted string
my $output = qx'ls \
-l';
This will work fine unless you have used Perl variables in the string that you want to be interpolated
Original post
The problem is that the shell removes newlines preceded by backslashes from the command string before executing it. Without that step the command is invalid
So you must do the same thing yourself in Perl, and to do that you must put the command in a temporary variable
use strict;
use warnings 'all';
my $cmd = <<'END';
tar --exclude="*/node_modules" \
--exclude="*/vendor" \
--exclude='.git' \
-zvcf /tmp/robot.tgz .
END
$cmd =~ s/\\\n//g;
my $output = `$cmd`;
There is no need for the backslashes of course; you can simply use newlines and remove those before executing the command
Or you may prefer to wrap the operations in a subroutine, like this
use strict;
use warnings 'all';
my $output = do_command(<<'END');
tar --exclude="*/node_modules" \
--exclude="*/vendor" \
--exclude='.git' \
-zvcf /tmp/robot.tgz .
END
sub do_command {
my ($cmd) = #_;
$cmd =~ s/\\\n//g;
`$cmd`;
}
I'm having an issue trying to capture the output of a sed command in a makefile variable.
JS_SRC:=$(shell sed -n 's#.*src="\([^"]*\.js\).*#\1#p' index.html)
Which gives me
sed: -e expression #1, char 34: unknown option tos'
`
I've been trying to escape things and the like, but am always given that error.
All variations of escaping I have run, run fine from the terminal.
How does a makefile call the shell command?. /usr/bin/sh -c "cmd?" or something different?.
Somethings being interpolated but I have no idea what.
JS_SRC:=$(shell sed -n "s/.*src=\"\\([^\"]*\\.js\\).*/\\1/p" index.html)
Appears to work. I figured this out via running make -d and seeing the process it was creating.
What was baffling is that it did different things with ' vs " in the sed argument. " is run with /bin/sh -c "args" so I was able to tweak the escaping to get what I needed to appear there. Using ' seems to invoke sed directly.
There is a whole heap of escaping, that i imagine is unnecessary (I don't need to interpolate variables in the sed expression, but it sends it to a shell I understand. So it will have to do ! :)