From 3df80b5afbebbf3af63b49fe98a3faecd2b68439 Mon Sep 17 00:00:00 2001
From: Jan T <jan@jantuomi.fi>
Date: Thu, 13 Nov 2025 11:31:30 +0000
Subject: Initial commit

---
 tools/filter | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)
 create mode 100755 tools/filter

(limited to 'tools/filter')

diff --git a/tools/filter b/tools/filter
new file mode 100755
index 0000000..94258d0
--- /dev/null
+++ b/tools/filter
@@ -0,0 +1,25 @@
+#!/bin/sh
+
+if [ -z "$1" ]; then
+    echo "Usage: $0 <command>"
+    echo ""
+    echo "Run the given test expression for each newline-separated line in stdin, and echo only the lines that return zero."
+    echo "(Think filter in many programming languages)."
+    echo 'The iterator variable is called "$ELEM", and the index variable is called "$IDX".'
+    exit 1
+fi
+
+i=0
+while IFS=$'\n' read -r line; do
+    j=0
+    for item in $line; do
+        eval "X${j}='$item'"
+        j=$((j+1))
+    done
+
+    IDX=$i ELEM="$line" eval "test $1"
+    if [ $? -eq 0 ]; then
+        echo "$line"
+    fi
+    i=$((i+1))
+done
-- 
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