add terminal check (to print color); also usage of terinfo tput OR color codes

Author: Anton-Latukha

scripts/install-nix-from-closure.sh

@@ -97,13 +97,25 @@ readonly appname="$0"
 ###  CLI control constants
 ###############################
 {
-# tput is not present on some systems (Alpine Linux), this trick with printf allows to store, not 'codes' - literal symbols
-readonly red=$(printf '\033[1;31m')
-readonly green=$(printf '\033[1;32m')
-readonly yellow=$(printf '\033[1;33m')
-readonly blue=$(printf '\033[1;34m')
-readonly bold=$(printf '\033[1m')
-readonly reset=$(printf '\033[0;m') # Reset to default output
+if test -t ; then    # File descriptor is associated with a terminal - output colors
+    if tput colors; then
+        # use tput and terminfo DB
+        readonly red=$(tput setaf 1)
+        readonly green=$(tput setaf 2)
+        readonly yellow=$(tput setaf 3)
+        readonly blue=$(tput setaf 4)
+        readonly bold=$(tput smso)
+        readonly reset=$(tput sgr0) # Reset to default output
+    else
+        # tput is not present on some systems (Alpine Linux), this trick with printf allows to store, not 'codes' - literal symbols
+        readonly red=$(printf '\033[1;31m')
+        readonly green=$(printf '\033[1;32m')
+        readonly yellow=$(printf '\033[1;33m')
+        readonly blue=$(printf '\033[1;34m')
+        readonly bold=$(printf '\033[1m')
+        readonly reset=$(printf '\033[0;m') # Reset to default output
+    fi
+fi
 }
 ###############################
 ###  CLI output functions