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IDProjectCategoryView StatusDate SubmittedLast Update
0000099tcshGeneralpublic2019-08-13 14:442022-08-09 09:53
Reporterxdelaruelle Assigned Tochristos  
PrioritynormalSeverityminorReproducibilityalways
Status assignedResolutionopen 
Product Version6.21.00 
Summary0000099: use of :q in back-tick context leads to erroneous extra history entries
DescriptionI am developing a tool called Modules (http://modules.sourceforge.net/) which enables to dynamically update user's shell environment. In short, this tool provides a shell alias called `module` which evaluates in the current shell the output of a script producing shell code.

The `module` command is currently defined this way:

  $ alias module 'eval "`/usr/share/Modules/libexec/modulecmd.tcl tcsh \!*:q`"'

Which leads to erroneous entries in the ~/.history file:

  #+1565705427
  module load foo bar
  #+1565705427
  load foo bar#+1565705430
  history

All arguments passed from the alias to the modulecmd.tcl script are added as a second history line. These erroneous entries seem to come from the use of the quote modifier `:q` within a back-tick context ``.

Some explanation on the use of the quote modifier :q in this alias: as the modulecmd.tcl script outputs shell codes, it contains sometime special characters like curly braces, so the result of the script execution is enclosed in double quotes to pass it to eval. In this situation to correctly obtain quoted arguments, the quote modifier is used.

The issue has been reproduced on tcsh versions 6.18, 6.19, 6.20 and 6.21.
Steps To ReproduceTo reproduce the issue on a small example, here is a script that produces some shell code (to define an alias or set an environment variable):

$ cat ./dispatch
#!/bin/csh
if ( $#argv != 1 ) then
  echo echo should get exactly 1 arg
  exit 1
endif

switch ( $argv[1] )
case myname:
  echo alias myname getent\\ passwd\\ \\\$USER\ \\\|\\ awk\\ -F:\\ \\\'\\\{print\ \\\$5\\\}\\\';
  breaksw;
case "":
  echo setenv EMPTY 1;
  breaksw;
endsw

$ echo $tcsh
6.21.00

Here we define the shell alias that calls the script and evaluates the shell code this script outputs:

$ alias tuneenv 'eval "`./dispatch \!*:q`"'

Then we use the alias:

$ tuneenv ""
$ echo $EMPTY
1
$ tuneenv myname
$ myname
Xavier
$ exit

Looking at history file, erroneous entries can be seen:

$ tail ~/.history
#+1565702553
tuneenv ""
#+1565702553
""#+1565702559
echo $EMPTY
#+1565702565
tuneenv myname
#+1565702565
myname#+1565702567
myname
Additional InformationSome additional tests to demonstrate the need to enclose script result in double quotes to pass it to eval:

$ alias tuneenv 'eval `./dispatch \!*`'
$ tuneenv myname
Missing '}'.

So without the double quotes, the shell alias myname which contains curly braces cannot be set

Then if we enclose script result in double quotes, !* should get the quote modifier applied to correctly transmit quoted arguments:

$ alias tuneenv 'eval "`./dispatch \!*`"'
$ tuneenv myname
$ myname
Xavier
$ tuneenv ""
should get exactly 1 arg

Without :q, the "" argument is not transmitted to the dispatch script.
TagsNo tags attached.

Activities

xdelaruelle

2019-08-13 14:44

reporter  

dispatch (279 bytes)    
#!/bin/csh

if ( $#argv != 1 ) then
  echo echo should get exactly 1 arg
  exit 1
endif

switch ( $argv[1] )
case myname:
  echo alias myname getent\\ passwd\\ \\\$USER\ \\\|\\ awk\\ -F:\\ \\\'\\\{print\ \\\$5\\\}\\\';
  breaksw;
case "":
  echo setenv EMPTY 1;
  breaksw;
endsw
dispatch (279 bytes)   

christos

2019-10-19 18:54

manager   ~0003317

Sorry, I can't reproduce it with 6.21.00 on either Linux or NetBSD. Did that break with 6.21.00 or the bug was always there?

xdelaruelle

2019-10-20 15:21

reporter   ~0003318

I get the exact same result whether I test this on tcsh version 6.18, 6.19, 6.20 and 6.21 on a Linux system.

Here are the details of the tcsh 6.21.00 ran:

$ echo $version
tcsh 6.21.00 (Astron) 2019-05-08 (x86_64-unknown-linux) options wide,nls,dl,al,kan,sm,rh,color,filec

With that shell, applying code sequence described in 'Steps To Reproduce' section with dispatch script attached to this ticket (shebang adapted to match the tcsh shell ran), the same erroneous ~/.history file is obtained (as described in section).

Issue History

Date Modified Username Field Change
2019-08-13 14:44 xdelaruelle New Issue
2019-08-13 14:44 xdelaruelle File Added: dispatch
2019-10-19 18:46 christos Assigned To => christos
2019-10-19 18:46 christos Status new => assigned
2019-10-19 18:54 christos Status assigned => feedback
2019-10-19 18:54 christos Note Added: 0003317
2019-10-20 15:21 xdelaruelle Note Added: 0003318
2019-10-20 15:21 xdelaruelle Status feedback => assigned