os400: fix shellcheck warnings in scripts

- use `$()` instead of backticks, and re-arrange double-quotes inside.
- add missing `|| exit 1` to `cd` calls. (could be dropped by using `set -eu`.)
- add `-n` to a few `if`s.
- shorten redirections by using `{} >` (as shellcheck recommended).
- silence warnings where variables were detected as unused (SC2034).
- a couple misc updates to silence warnings.
- switch to bash shebang for `-ot` feature.
- split two lines to unbreak syntax highlighting in my editor. (`$(expr \`, `$(dirname \`)

Also enable CI checks for OS/400 shell scripts.

Ref: d88b9bcdaf
Closes #1358

os400/make-src.sh

@@ -1,13 +1,13 @@
-#!/bin/sh
+#!/usr/bin/env bash
 # Copyright (C) The libssh2 project and its contributors.
 # SPDX-License-Identifier: BSD-3-Clause
 #
 #       libssh2 compilation script for the OS/400.
 #
 
-SCRIPTDIR=`dirname "${0}"`
+SCRIPTDIR=$(dirname "${0}")
 . "${SCRIPTDIR}/initscript.sh"
-cd "${TOPDIR}/src"
+cd "${TOPDIR}/src" || exit 1
 
 
 #       Function to extract external prototypes from header files.
@@ -48,10 +48,12 @@ fi
 
 #      Create and compile the identification source file.
 
-echo '#pragma comment(user, "libssh2 version '"${LIBSSH2_VERSION}"'")' > os400.c
-echo '#pragma comment(user, __DATE__)' >> os400.c
-echo '#pragma comment(user, __TIME__)' >> os400.c
-echo '#pragma comment(copyright, "See COPYING file. OS/400 version by P. Monnerat")' >> os400.c
+{
+        echo '#pragma comment(user, "libssh2 version '"${LIBSSH2_VERSION}"'")'
+        echo '#pragma comment(user, __DATE__)'
+        echo '#pragma comment(user, __TIME__)'
+        echo '#pragma comment(copyright, "See COPYING file. OS/400 version by P. Monnerat")'
+} > os400.c
 make_module     OS400           os400.c
 LINK=                           # No need to rebuild service program yet.
 MODULES=
@@ -80,28 +82,28 @@ fi
 
 #       Get source list.
 
-cat Makefile.inc                                                        |
-  sed -e ':begin'                                                       \
-    -e '/\\$/{'                                                         \
-    -e 's/\\$/ /'                                                       \
-    -e 'N'                                                              \
-    -e 'bbegin'                                                         \
-    -e '}'                                                              \
-    -e 's/\n//g'                                                        \
-    -e 's/[[:space:]]*$//'                                              \
-    -e 's/^\([A-Za-z][A-Za-z0-9_]*\)[[:space:]]*=[[:space:]]*\(.*\)/\1="\2"/' \
-    -e 's/\$(\([A-Za-z][A-Za-z0-9_]*\))/${\1}/g'                        \
-        > tmpscript.sh
+sed -e ':begin'                                                         \
+  -e '/\\$/{'                                                           \
+  -e 's/\\$/ /'                                                         \
+  -e 'N'                                                                \
+  -e 'bbegin'                                                           \
+  -e '}'                                                                \
+  -e 's/\n//g'                                                          \
+  -e 's/[[:space:]]*$//'                                                \
+  -e 's/^\([A-Za-z][A-Za-z0-9_]*\)[[:space:]]*=[[:space:]]*\(.*\)/\1="\2"/' \
+  -e 's/\$(\([A-Za-z][A-Za-z0-9_]*\))/${\1}/g'                          \
+      < Makefile.inc > tmpscript.sh
 . ./tmpscript.sh
 
 
 #       Compile the sources into modules.
 
-INCLUDES="'`pwd`'"
+# shellcheck disable=SC2034
+INCLUDES="'$(pwd)'"
 
 for SRC in "${TOPDIR}/os400/os400sys.c" "${TOPDIR}/os400/ccsid.c"       \
            ${CSOURCES} macros.c
-do      MODULE=`db2_name "${SRC}"`
+do      MODULE=$(db2_name "${SRC}")
         make_module "${MODULE}" "${SRC}"
 done
 
@@ -112,7 +114,7 @@ if action_needed "${LIBIFSNAME}/${STATBNDDIR}.BNDDIR"
 then    LINK=YES
 fi
 
-if [ "${LINK}" ]
+if [ -n "${LINK}" ]
 then    rm -rf "${LIBIFSNAME}/${STATBNDDIR}.BNDDIR"
         CMD="CRTBNDDIR BNDDIR(${TARGETLIB}/${STATBNDDIR})"
         CMD="${CMD} TEXT('libssh2 API static binding directory')"
@@ -145,10 +147,10 @@ fi
 
 #       Gather the list of symbols to export.
 
-EXPORTS=`cat "${TOPDIR}"/include/*.h "${TOPDIR}/os400/macros.h"         \
+EXPORTS=$(cat "${TOPDIR}"/include/*.h "${TOPDIR}/os400/macros.h"        \
              "${TOPDIR}/os400/libssh2_ccsid.h"                          |
          extproto                                                       |
-         sed -e 's/(.*//;s/[^A-Za-z0-9_]/ /g;s/ *$//;s/^.* //'`
+         sed -e 's/(.*//;s/[^A-Za-z0-9_]/ /g;s/ *$//;s/^.* //')
 
 #       Create the service program exportation file in DB2 member if needed.
 
@@ -158,7 +160,7 @@ if action_needed "${BSF}" Makefile.am
 then    LINK=YES
 fi
 
-if [ "${LINK}" ]
+if [ -n "${LINK}" ]
 then    echo " STRPGMEXP PGMLVL(*CURRENT) SIGNATURE('LIBSSH2_${SONAME}')" \
             > "${BSF}"
         for EXPORT in ${EXPORTS}
@@ -175,7 +177,7 @@ if action_needed "${LIBIFSNAME}/${SRVPGM}.SRVPGM"
 then    LINK=YES
 fi
 
-if [ "${LINK}" ]
+if [ -n "${LINK}" ]
 then    CMD="CRTSRVPGM SRVPGM(${TARGETLIB}/${SRVPGM})"
         CMD="${CMD} SRCFILE(${TARGETLIB}/TOOLS) SRCMBR(BNDSRC)"
         CMD="${CMD} MODULE(${TARGETLIB}/OS400)"
@@ -199,7 +201,7 @@ if action_needed "${LIBIFSNAME}/${DYNBNDDIR}.BNDDIR"
 then    LINK=YES
 fi
 
-if [ "${LINK}" ]
+if [ -n "${LINK}" ]
 then    rm -rf "${LIBIFSNAME}/${DYNBNDDIR}.BNDDIR"
         CMD="CRTBNDDIR BNDDIR(${TARGETLIB}/${DYNBNDDIR})"
         CMD="${CMD} TEXT('libssh2 API dynamic binding directory')"