+# Text functions.
+
+# Filter a list by regexp.
+pure function filter (pat, xs) returning strings = @{
+ for f in %xs; do echo "$f"; done | grep -E -- %pat
+}
+
+# Filter out a list by regexp.
+pure function filter-out (pat, xs) returning strings = @{
+ for f in %xs; do echo "$f"; done | grep -v -E -- %pat
+}
+
+# Head of a list.
+pure function head (xs) returning string = @{
+ for f in %xs; do
+ echo "$f"
+ exit 0
+ done
+}
+
+# Join two lists.
+pure function join (xs, ys) returning strings = @{
+ for f in %xs %ys; do echo "$f"; done
+}
+
+# Last element of a list.
+pure function last (xs) returning string = @{
+ for f in %xs; do
+ r="$f"
+ done
+ echo "$r"
+}
+
+# n'th element of a list.
+pure function nth (n, xs) returning string = @{
+ i=0
+ r=
+ for f in %xs; do
+ if [ $i -eq %n ]; then r="$f"; fi
+ ((++i))
+ done
+ echo "$r"
+}
+
+# Sort + uniq a list.
+pure function sort (xs) returning strings = @{
+ for f in %xs; do echo "$f"; done | sort -u
+}
+
+# Split a string into a list.
+# https://superuser.com/a/1066541
+pure function split (s) returning strings = @{
+ s=%s
+ eval 'for f in '$s'; do echo "$f"; done'
+}
+
+# Substitute.
+pure function subst (from, to, text) returning string = @{
+ # We need to replace any / characters in ‘to’ with escaped ones.
+ to="$( echo -n %to | sed 's,/,\\/,g' )"
+ echo %text | sed -E s/%from/$to/g
+}
+
+# Tail of a list.
+pure function tail (xs) returning strings = @{
+ drop=1
+ for f in %xs; do
+ if [ -z "$drop" ]; then echo "$f"; fi
+ drop=
+ done
+}
+
+#----------------------------------------------------------------------