Great! Thanks for the check, this is just what I meant ;-)!

So this seems to be a good solution. We should just change the directory part of the shebang to '/usr/bin/env '

Very nice point!

Using '.local/bin/<executable>' is one solution, but as you said it will potentially cause problems when users change directory within a recipe (it happens, for example when building the LaTeX paper in 'paper.mk'),

I have sometimes been forced to do this in my research because some research software only write their outputs in the current directory, so the only way to avoid writing in the source directory is to 'cd' to the special directory, run it there, and come back up to the source!

Maybe using the host's 'env' is the most portable solution (because if we want to use Maneage's 'env', we'll have the same length-problem!).

The reason is that within the project's Make (as called in the top-level 'project' script) we completely close-off the host's environment and have our own PATH. So 'env PROGNAME' should expand to the PROGNAME in Maneage, right? Even if 'env' doesn't belong to Maneage itself.

This is indeed an important point! Thanks for bringing it up ;-)!

I just tried it (changing '.build/software/installed' to '.local') and indeed found many such scripts!

$ for i in $(file .local/bin/*|grep script |awk '{print $1}' |tr -d ':'); do printf "${i} ::: " ; head -n1 $i ; done
.local/bin/astscript-sort-by-night ::: #!/bin/sh
.local/bin/autopoint ::: #! /bin/sh
.local/bin/bashbug ::: #!/bin/sh -
.local/bin/bzdiff ::: #!/bin/sh
.local/bin/bzgrep ::: #!/bin/sh
.local/bin/bzmore ::: #!/bin/sh
.local/bin/c_rehash ::: #!/usr/bin/env perl
.local/bin/curl-config ::: #! /bin/sh
.local/bin/dvipdf ::: #!/bin/sh
.local/bin/egrep ::: #!/my/build/directory/software/installed/bin/bash
.local/bin/eps2eps ::: #!/bin/sh
.local/bin/fgrep ::: #!/my/build/directory/software/installed/bin/bash
.local/bin/gettextize ::: #! /bin/sh
.local/bin/gettext.sh ::: #! /bin/sh
.local/bin/git-cvsserver ::: #!/usr/bin/perl
.local/bin/glibtool ::: #! /bin/bash
.local/bin/glibtoolize ::: #! /bin/sh
.local/bin/gsbj ::: #!/bin/sh
.local/bin/gsdj ::: #!/bin/sh
.local/bin/gsdj500 ::: #!/bin/sh
.local/bin/gsl-config ::: #! /bin/sh
.local/bin/gslj ::: #!/bin/sh
.local/bin/gslp ::: #!/bin/sh
.local/bin/gsnd ::: #!/bin/sh
.local/bin/gunzip ::: #!/bin/bash
.local/bin/gzexe ::: #!/bin/bash
.local/bin/libpng16-config ::: #! /bin/sh
.local/bin/lprsetup.sh ::: #!/bin/sh
.local/bin/ncursesw6-config ::: #!/bin/bash
.local/bin/pdf2dsc ::: #! /bin/sh
.local/bin/pdf2ps ::: #!/bin/sh
.local/bin/pdftexi2dvi ::: #!/bin/sh
.local/bin/pf2afm ::: #!/bin/sh
.local/bin/pfbtopfa ::: #!/bin/sh
.local/bin/pod2texi ::: #! /my/build/directory/software/installed/bin/perl
.local/bin/pphs ::: #!/bin/sh
.local/bin/printafm ::: #!/bin/sh
.local/bin/ps2ascii ::: #!/bin/sh
.local/bin/ps2epsi ::: #!/bin/sh
.local/bin/ps2pdf ::: #!/bin/sh
.local/bin/ps2pdf12 ::: #!/bin/sh
.local/bin/ps2pdf13 ::: #!/bin/sh
.local/bin/ps2pdf14 ::: #!/bin/sh
.local/bin/ps2pdfwr ::: #!/bin/sh
.local/bin/ps2ps ::: #!/bin/sh
.local/bin/ps2ps2 ::: #!/bin/sh
.local/bin/texi2any ::: #! /my/build/directory/software/installed/bin/perl
.local/bin/texi2dvi ::: #! /bin/sh
.local/bin/texi2pdf ::: #!/bin/sh
.local/bin/texindex ::: #!/bin/sh
.local/bin/uncompress ::: #!/bin/bash
.local/bin/unix-lpr.sh ::: #!/bin/sh
.local/bin/updatedb ::: #! /bin/sh
.local/bin/xml2-config ::: #! /bin/sh
.local/bin/xzdiff ::: #!/bin/bash
.local/bin/xzgrep ::: #!/bin/bash
.local/bin/xzless ::: #!/bin/bash
.local/bin/xzmore ::: #!/bin/bash
.local/bin/zcat ::: #!/bin/bash
.local/bin/zcmp ::: #!/bin/bash
.local/bin/zdiff ::: #!/bin/bash
.local/bin/zegrep ::: #!/bin/bash
.local/bin/zfgrep ::: #!/bin/bash
.local/bin/zforce ::: #!/bin/bash
.local/bin/zgrep ::: #!/bin/bash
.local/bin/zipgrep ::: #!/bin/sh
.local/bin/zless ::: #!/bin/bash
.local/bin/zmore ::: #!/bin/bash
.local/bin/znew ::: #!/bin/bash

Its interesting how some of them have already been so well written, such that they use the given 'SHELL' environment variable in their shebangs and have already accounted for this (some Texinfo and grep scripts, not all!).

I noticed that Gnuastro's 'astscript-sort-by-night' script also has this problem, I tried implementing a fix to it, but in the middle, I had second-thoughts: for example the "SHELL" environment variable my be set temporarily to some temporarily-built file. So if we use it in a permanently installed file, the program will crash. So I am not too sure now about its usefulness for individual programs. Its a higher-level decision for systems like Maneage.

We can add such a step in the 'reproduce/software/shell/configure.sh' script, after the building of software has finished.

We should just use our own installed programs in the loop (as we do in all the steps of 'configure.sh' after installing programs). For example '.local/bin/file' and etc, like this:

for i in $(.local/bin/file .local/bin/* | .local/bin/grep script | .local/bin/awk '{print $1}' | .local/bin/tr -d ':'); do .local/bin/printf "${i} ::: " ; .local/bin/head -n1 $i ; done