Search code examples
bashmakefileechocatdash-shell

Run echo and redirect it to cat with dash shell

I want make one-liner that creates zipped file with python code. However when I run it in Makefile, it uses the default shell (dash). Is the

bash$ dash
dash$ zip --exclude '.git/*' --exclude '*.swp' --exclude '*.pyc' --exclude 'tool' --exclude Makefile -r - . | cat <(echo '#!/usr/bin/env python') - > externaltool
dash: 1: Syntax error: "(" unexpected
dash$ exit

But in bash it works perfectly well

bash$ zip --exclude '.git/*' --exclude '*.swp' --exclude '*.pyc' --exclude 'externaltool' --exclude Makefile -r - . | cat <(echo '#!/usr/bin/env python') - > externaltool
  adding: common/ (stored 0%)
  adding: common/config.py (deflated 19%)
  adding: common/cmdwrap.py (deflated 65%)
  adding: common/extconfig.py (deflated 71%)
  adding: common/commands.py (deflated 19%)
  adding: common/__init__.py (stored 0%)
  adding: __main__.py (deflated 45%)

Is there any method to express cat <(echo '#!/usr/bin/env python') - in dash ?

I know I can add to Makefile

SHELL := /bin/bash

but it is just workaround rather than pernament solution.

Solution

  • No. dash doesn't support process substitution.

    But that's also a rather strange way to do what you want there.

    Two simpler (and dash compatible unless I'm sorely mistaken) ways are:

    { echo '#!/usr/bin/env python'; zip --exclude '.git/*' --exclude '*.swp' --exclude '*.pyc' --exclude 'tool' --exclude Makefile -r - .; } > externaltool

    and

    echo '#!/usr/bin/env python' > externaltool
zip --exclude '.git/*' --exclude '*.swp' --exclude '*.pyc' --exclude 'tool' --exclude Makefile -r - . >> externaltool`