An example of a bash script with test blocks (2024)

Here is a screenshot - click on it to enlarge:

It shows a script that I use to convert a series of PDFs into an animated gif. It is explained, as a tool, in this section of one of my pages about Maxima.

I don't write Bash code often, and I would never be able to remember what the tricks in red below do

and_run      () { echo $*; $*; }
cdr          () { echo ${@:2}; }
add_1zs      () { for i in $*; do echo $i 1-z; done; }
makeboth     () { $ECHO makeflipbook $(cdr $*);
                  $ECHO makeanim $1 $2; }
makeflipbook () { $ECHO qpdf --empty --pages $(add_1zs $(cdr $*)) -- $1; }
makeanim     () {
  $ECHO convert -alpha deactivate ${VERBOSE:+-verbose} \
                -delay $DELAY -loop 0 -density $DENSITY $2 $1
}

without 1) links to the documentation and 2) examples. The links to the documentation appear right above that code in the screenshot - let me copy them here:

# See:
#   (find-bashnode "Environment" "parameter assignments")
#   (find-bashnode "Shell Parameter Expansion" "${@:7}")
#   (find-bashnode "Shell Parameter Expansion" "${PARAMETER:+WORD}")

These links work much better in Emacs than in the browser. If you click on the `")' at the end of one of the `find-bashnode' links above you will see that it goes to a page of the Bash manual, but it "ignores the pos-spec-list"... while in Emacs the second link searches for the first occurrence of "${@:7}", as shown here:

So that solves the first half of my problem - "1) links to the documentation".

The second half of my problem - "2) examples" - is much trickier. For me it is much easier to test the individual functions in a bash script if it can be used both "as a library" and "as a script"; and the trick that lets it be used in both ways is an

eval "$*"

at the end of the script - see here, or in this screenshot, that also shows its comments and a test block:

Test:

* (eepitch-shell)
* (eepitch-kill)
* (eepitch-shell)
rm -fv    /tmp/mkanim1.sh
wget -P   /tmp/ http://anggtwu.net/myqdraw/mkanim1.sh
chmod 755 /tmp/mkanim1.sh
# (find-anchor "/tmp/mkanim1.sh")
# (find-anchor "/tmp/mkanim1.sh" "makeanim-tests")
# (find-anchor "/tmp/mkanim1.sh" "latex-tests")
# (find-anchor "/tmp/mkanim1.sh" "eval-tests")