This works in Windows console as expected:
set A="qwerty" && echo %A%
the output: "qwerty"
But when I try to run the same commands in NPM scipts:
package.json:
"scripts": {
"qwerty": "set A=\"qwerty\" && echo %A%"
}
> npm run qwerty
the output is: %A%
Am I doing something wrong or it just shouldn't work that way when run by NPM?
Your example set A="qwerty" && echo %A% isn't correct. Variables in the cmd prompt / a batch file are expanded once per line / command:
==> set "A="
==> echo %A%
%A%
==> set A="qwerty" && echo %A%
%A%
==> echo %A%
"qwerty"
The
SETcommand was first introduced with MS-DOS 2.0 in March 1983, at that time memory and CPU were very limited and the expansion of variables once per line was enough.
A workaround using the CALL command:
==> set "A="
==> echo %A%
%A%
==> set A="qwerty" && CALL echo %A%
"qwerty"
For the sake of completeness, the following batch script shows the mechanism of percent expansion and its combination with the CALL command in detail (note doubled % percent signs in the batch file CALL Echo %%_var%%):
@ECHO OFF
SETLOCAL
if NOT "%~1"=="" ECHO ON
echo 1st:
Set "_var=first"
Set "_var=second" & Echo %_var% & CALL Echo %%_var%%
echo 2nd:
Set "_var=first"
Set "_var=second" & CALL Echo %%_var%% & Echo %_var%
Output, echo OFF:
==> D:\bat\SO\55237418.bat
1st:
first
second
2nd:
second
first
Output, echo ON:
==> D:\bat\SO\55237418.bat on
==> echo 1st:
1st:
==> Set "_var=first"
==> Set "_var=second" & Echo first & CALL Echo %_var%
first
second
==> echo 2nd:
2nd:
==> Set "_var=first"
==> Set "_var=second" & CALL Echo %_var% & Echo first
second
first
set A="qwerty" && echo %A% seemed to be working in my console because of the previous run which actually hadn't worked but I hadn't noticed that and saw only it working in the next runs.What I found so far is that these commands in order to work properly must be in different scripts and run in a specific order. So, here is the way how it works:
"scripts": {
"aaa": "set TMP=test && npm run bbb",
"bbb": "echo %TMP%"
}
npm run aaa
output:
test
But this one wouldn't work:
"scripts": {
"aaa": "set TMP=test",
"bbb": "npm run aaa && echo %TMP%"
}
npm run bbb
output: <just empty>
It looks like two separate npm run commands are required to find the created variable: the variable should be created in the first npm run and could be found in the second one.
set "A=", then try it again, then you will get%A%echoed. To write and read a variable in the same line or block of code you need delayed expansion, soset "A=qwerty" & echo(!A!when having started the command prompt withcmd /V:ON. Alternatively, tryset "A=qwerty" & call echo(%^A%(although this might still fail under some circumstances)...