Fix: mk-job (linux) support versions without perl again

Current Linux Distributions like RHEL 8 + 9 do not install Perl as default.
So with the Update Checkmk 2.3, mk-job fails there since an earlier workaround for aix/ solaris to get a timestamp using perl, was made a default now for as well Linux.

This fix tries to restore the function on GNU Linux again if perl is missing, but without reverting the use of perl as default.
Since GNU date should always have the %s parameter, just BSD or BusyBox can lack the support, that's maybe a reasonable approach.

CMK-20768
closes: #775

Change-Id: Icf9e182511ef7fa0898883710189b2fcf0960e66

Author: Bastian-Kuhn

agents/mk-job

@@ -72,7 +72,15 @@ main() {
         rm "${RUNNING_FILE}" 2>/dev/null
     }
 
-    echo "start_time $(perl -e 'print time')" >"${TMP_FILE}" 2>/dev/null
+    try_perl() {
+        perl -e 'print "start_time " . time . "\n"' >"${TMP_FILE}" 2>/dev/null
+    }
+
+    fallback_date() {
+        date +"start_time %s" >"${TMP_FILE}" 2>/dev/null
+    }
+    try_perl || fallback_date
+
     cp "${TMP_FILE}" "${RUNNING_FILE}" 2>/dev/null
 
     if [ ! -w "${RUNNING_FILE}" ]; then

agents/mk-job.aix

@@ -72,7 +72,15 @@ main() {
         rm "${RUNNING_FILE}" 2>/dev/null
     }
 
-    echo "start_time $(perl -e 'print time')" >"${TMP_FILE}" 2>/dev/null
+    try_perl() {
+        perl -e 'print "start_time " . time . "\n"' >"${TMP_FILE}" 2>/dev/null
+    }
+
+    fallback_date() {
+        date +"start_time %s" >"${TMP_FILE}" 2>/dev/null
+    }
+    try_perl || fallback_date
+
     cp "${TMP_FILE}" "${RUNNING_FILE}" 2>/dev/null
 
     if [ ! -w "${RUNNING_FILE}" ]; then

agents/mk-job.solaris

@@ -72,7 +72,15 @@ main() {
         rm "${RUNNING_FILE}" 2>/dev/null
     }
 
-    echo "start_time $(perl -e 'print time')" >"${TMP_FILE}" 2>/dev/null
+    try_perl() {
+        perl -e 'print "start_time " . time . "\n"' >"${TMP_FILE}" 2>/dev/null
+    }
+
+    fallback_date() {
+        date +"start_time %s" >"${TMP_FILE}" 2>/dev/null
+    }
+    try_perl || fallback_date
+
     cp "${TMP_FILE}" "${RUNNING_FILE}" 2>/dev/null
 
     if [ ! -w "${RUNNING_FILE}" ]; then