diff --git a/Makefile.am b/Makefile.am
index 7d1f8d5..d989866 100755
--- a/Makefile.am
+++ b/Makefile.am
@@ -4,7 +4,7 @@
 
 AUTOMAKE_OPTIONS = -Wno-portability
 SUBDIRS = src
-SHELL = /bin/bash
+SHELL = /bin/sh
 
 BUILDHOST ?= $(shell [ -f .env ] && . ./.env 2>/dev/null && printf '%s' "$$BUILDHOST")
 TOR_BUILDHOST ?= $(shell [ -f .env ] && . ./.env 2>/dev/null && printf '%s' "$$TOR_BUILDHOST")
@@ -61,7 +61,7 @@ sig:
 	perl -i -pe "s/20\d\d\d\d\d\d/$(YYYYMMDD)/" parallel-latest.tar.*directive
 	gpg --clearsign --yes parallel-latest.tar.bz2.directive
 
-	(echo '#!/bin/bash'; \
+	(echo '#!/bin/sh'; \
 	 echo; \
 	 echo "# To check the signature run:"; \
 	 echo "#   echo | gpg"; \
@@ -75,7 +75,7 @@ sig:
 	) > parallel-$(YYYYMMDD).tar.bz2.sig
 	chmod +x parallel-$(YYYYMMDD).tar.bz2.sig
 
-	(echo '#!/bin/bash'; \
+	(echo '#!/bin/sh'; \
 	 echo; \
 	 echo "# To check the signature run:"; \
 	 echo "#   echo | gpg"; \
@@ -126,7 +126,7 @@ alphaupload:
 	perl -i -pe "s/20\d\d\d\d\d\d/$(YYYYMMDD)/" parallel-latest.tar.*directive
 	gpg --clearsign --yes parallel-latest.tar.bz2.directive
 
-	(echo '#!/bin/bash'; \
+	(echo '#!/bin/sh'; \
 	 echo; \
 	 echo "# To check the signature run:"; \
 	 echo "#  echo | gpg"; \
@@ -139,7 +139,7 @@ alphaupload:
 	 gpg -ab -o - parallel-$(YYYYMMDD).tar.bz2; \
 	) > parallel-$(YYYYMMDD).tar.bz2.sig
 
-	(echo '#!/bin/bash'; \
+	(echo '#!/bin/sh'; \
 	 echo; \
 	 echo "# To check the signature run:"; \
 	 echo "#  echo | gpg"; \
diff --git a/Makefile.in b/Makefile.in
index eeb280a..0436c23 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -241,7 +241,7 @@ PACKAGE_URL = @PACKAGE_URL@
 PACKAGE_VERSION = @PACKAGE_VERSION@
 PATH_SEPARATOR = @PATH_SEPARATOR@
 SET_MAKE = @SET_MAKE@
-SHELL = /bin/bash
+SHELL = /bin/sh
 STRIP = @STRIP@
 VERSION = @VERSION@
 abs_builddir = @abs_builddir@
@@ -842,7 +842,7 @@ sig:
 	perl -i -pe "s/20\d\d\d\d\d\d/$(YYYYMMDD)/" parallel-latest.tar.*directive
 	gpg --clearsign --yes parallel-latest.tar.bz2.directive
 
-	(echo '#!/bin/bash'; \
+	(echo '#!/bin/sh'; \
 	 echo; \
 	 echo "# To check the signature run:"; \
 	 echo "#   echo | gpg"; \
@@ -856,7 +856,7 @@ sig:
 	) > parallel-$(YYYYMMDD).tar.bz2.sig
 	chmod +x parallel-$(YYYYMMDD).tar.bz2.sig
 
-	(echo '#!/bin/bash'; \
+	(echo '#!/bin/sh'; \
 	 echo; \
 	 echo "# To check the signature run:"; \
 	 echo "#   echo | gpg"; \
@@ -907,7 +907,7 @@ alphaupload:
 	perl -i -pe "s/20\d\d\d\d\d\d/$(YYYYMMDD)/" parallel-latest.tar.*directive
 	gpg --clearsign --yes parallel-latest.tar.bz2.directive
 
-	(echo '#!/bin/bash'; \
+	(echo '#!/bin/sh'; \
 	 echo; \
 	 echo "# To check the signature run:"; \
 	 echo "#  echo | gpg"; \
@@ -920,7 +920,7 @@ alphaupload:
 	 gpg -ab -o - parallel-$(YYYYMMDD).tar.bz2; \
 	) > parallel-$(YYYYMMDD).tar.bz2.sig
 
-	(echo '#!/bin/bash'; \
+	(echo '#!/bin/sh'; \
 	 echo; \
 	 echo "# To check the signature run:"; \
 	 echo "#  echo | gpg"; \
diff --git a/src/env_parallel b/src/env_parallel
index 9c946ca..7c24987 100755
--- a/src/env_parallel
+++ b/src/env_parallel
@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/bin/sh
 
 # Copyright (C) 2016-2026 Ole Tange, http://ole.tange.dk and Free
 # Software Foundation, Inc.
@@ -23,17 +23,19 @@
 
 grepq() {
     # grep -q for systems without -q
-    grep >/dev/null 2>/dev/null "$@"
+    grep "$@" >/dev/null 2>&1
 }
 
 installer() {
-    source="$1"
-    script="$2"
-    into="$3"
-    if grepq $script "$into"; then
-	true already installed
+    source_command=$1
+    script=$2
+    into=$3
+
+    if grepq "$script" "$into"; then
+        : already installed
     else
-	echo $source \`which $script\` >> "$into"
+        script_path=$(command -v "$script" 2>/dev/null) || script_path=$script
+        printf '%s %s\n' "$source_command" "$script_path" >> "$into"
     fi
 }
 
@@ -47,11 +49,11 @@ while test $# -gt 0; do
 	  installer . env_parallel.zsh   "$HOME"/.zshenv
 	  installer source env_parallel.ksh "$HOME"/.kshrc
 	  installer source env_parallel.mksh "$HOME"/.mkshrc
-	  echo $SHELL | grepq /pdksh &&
+	  printf '%s\n' "${SHELL-}" | grepq /pdksh &&
 	      installer . env_parallel.pdksh "$HOME"/.profile
-	  echo $SHELL | grepq /ash &&
+	  printf '%s\n' "${SHELL-}" | grepq /ash &&
 	      installer . env_parallel.ash "$HOME"/.profile
-	  echo $SHELL | grepq /dash &&
+	  printf '%s\n' "${SHELL-}" | grepq /dash &&
 	      installer . env_parallel.dash "$HOME"/.profile
 	  installer source env_parallel.csh "$HOME"/.cshrc
 	  installer source env_parallel.tcsh "$HOME"/.tcshrc
@@ -71,7 +73,7 @@ while test $# -gt 0; do
   	  exit
       ;;
       *)
-  	echo "Unknown option: $key"
+  	printf '%s\n' "Unknown option: $key"
       ;;
   esac
   shift # past argument or value
@@ -91,7 +93,7 @@ bash:  Put this in $HOME/.bashrc:  . env_parallel.bash
 
 fish:  Put this in $HOME/.config/fish/config.fish:  . (which env_parallel.fish)
        E.g. by doing:
-         echo '. (which env_parallel.fish)' >> $HOME/.config/fish/config.fish
+         printf '%s\n' '. (which env_parallel.fish)' >> "$HOME/.config/fish/config.fish"
        Supports: variables, aliases, functions, arrays
 
 ksh:   Put this in $HOME/.kshrc:  source env_parallel.ksh
diff --git a/src/parset b/src/parset
index e3c36f1..df1ec3d 100755
--- a/src/parset
+++ b/src/parset
@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/bin/sh
 
 # Copyright (C) 2016-2026 Ole Tange, http://ole.tange.dk and Free
 # Software Foundation, Inc.
@@ -23,17 +23,19 @@
 
 grepq() {
     # grep -q for systems without -q
-    grep >/dev/null 2>/dev/null "$@"
+    grep "$@" >/dev/null 2>&1
 }
 
 installer() {
-    source="$1"
-    script="$2"
-    into="$3"
-    if grepq $script $into; then
-	true already installed
+    source_command=$1
+    script=$2
+    into=$3
+
+    if grepq "$script" "$into"; then
+        : already installed
     else
-	echo $source \`which $script\` >> $into
+        script_path=$(command -v "$script" 2>/dev/null) || script_path=$script
+        printf '%s %s\n' "$source_command" "$script_path" >> "$into"
     fi
 }
 
@@ -42,36 +44,36 @@ while test $# -gt 0; do
 
   case $key in
       -i|--install)
-	  installer . env_parallel.bash  $HOME/.bashrc
-	  installer . env_parallel.sh  $HOME/.shrc
-	  installer . env_parallel.zsh   $HOME/.zshenv
-	  installer source env_parallel.ksh $HOME/.kshrc
-	  installer source env_parallel.mksh $HOME/.kshrc
-	  echo $SHELL | grepq /pdksh &&
-	      installer . env_parallel.pdksh $HOME/.profile
-	  echo $SHELL | grepq /ash &&
-	      installer . env_parallel.ash $HOME/.profile
-	  echo $SHELL | grepq /dash &&
-	      installer . env_parallel.dash $HOME/.profile
-	  installer source env_parallel.csh $HOME/.cshrc
-	  installer source env_parallel.tcsh $HOME/.tcshrc
-	  mkdir -p $HOME/.config/fish
-	  grepq env_parallel.fish $HOME/.config/fish/config.fish ||
-  	    echo '. (which env_parallel.fish)' >> $HOME/.config/fish/config.fish
+	  installer . env_parallel.bash  "$HOME/.bashrc"
+	  installer . env_parallel.sh  "$HOME/.shrc"
+	  installer . env_parallel.zsh   "$HOME/.zshenv"
+	  installer source env_parallel.ksh "$HOME/.kshrc"
+	  installer source env_parallel.mksh "$HOME/.kshrc"
+	  printf '%s\n' "${SHELL-}" | grepq /pdksh &&
+	      installer . env_parallel.pdksh "$HOME/.profile"
+	  printf '%s\n' "${SHELL-}" | grepq /ash &&
+	      installer . env_parallel.ash "$HOME/.profile"
+	  printf '%s\n' "${SHELL-}" | grepq /dash &&
+	      installer . env_parallel.dash "$HOME/.profile"
+	  installer source env_parallel.csh "$HOME/.cshrc"
+	  installer source env_parallel.tcsh "$HOME/.tcshrc"
+	  mkdir -p "$HOME/.config/fish"
+	  grepq env_parallel.fish "$HOME/.config/fish/config.fish" ||
+  	    printf '%s\n' '. (which env_parallel.fish)' >> "$HOME/.config/fish/config.fish"
   	  echo 'Installed env_parallel in:'
-  	  echo "    " $HOME/.bashrc
-  	  echo "    " $HOME/.shrc
-  	  echo "    " $HOME/.zshenv
-  	  echo "    " $HOME/.config/fish/config.fish
-  	  echo "    " $HOME/.kshrc
-  	  echo "    " $HOME/.mkshrc
-  	  echo "    " $HOME/.profile
-  	  echo "    " $HOME/.cshrc
-  	  echo "    " $HOME/.tcshrc
+  	  echo "    " "$HOME/.bashrc"
+  	  echo "    " "$HOME/.shrc"
+  	  echo "    " "$HOME/.zshenv"
+  	  echo "    " "$HOME/.config/fish/config.fish"
+  	  echo "    " "$HOME/.kshrc"
+  	  echo "    " "$HOME/.mkshrc"
+  	  echo "    " "$HOME/.profile"
+  	  echo "    " "$HOME/.cshrc"
+  	  echo "    " "$HOME/.tcshrc"
   	  exit
       ;;
       *)
-  	echo "Unknown option: $key"
+  	printf '%s\n' "Unknown option: $key"
       ;;
   esac
   shift # past argument or value