1 files changed, 71 insertions, 0 deletions
diff --git a/scripts/whoneeds b/scripts/whoneeds
new file mode 100755
index 0000000..6f8f23c
--- /dev/null
+++ b/scripts/whoneeds
@@ -0,0 +1,71 @@
+#!/bin/bash
+# whoneeds package : shows explicitly installed packages that require some package
+
+# we use associative arrays to get uniqueness for "free"
+typeset -A root_packages
+typeset -A walked_nodes
+query="$1"
+
+function walk_nodes () {
+    local package="$1"
+
+    # if we've walked this node before, skip. This drastically
+    # reduces overhead for a relatively cheap operation
+    [[ "${walked_nodes[$package]}" -eq 1 ]] && return 0
+    walked_nodes["$package"]=1
+
+    # we do this so that we can make a single call to pacman
+    # to get both bits of information that we require
+    result=( $(LC_ALL=c pacman -Qi "$package" | awk -F':' \
+      'BEGIN { tag = ""; dependents = ""; explicit = 0 }
+       {
+          # since the formatting of the pacman output is more for human
+          # consumption than programmatic, we find ourselves with the following need.
+          # if we have two fields, then we know we have a proper identifier on the line
+          # so we store the identifier as a current tag
+          # All identifier checks are made against the current tag, which allows us
+          # to deal with instances where "Required By" spans lines
+          if (NF == 2) { tag = $1 }
+          if (tag ~ /^Required By[ ]*$/) {  dependents = dependents $(NF) }
+          if ($1 ~ /^Install Reason $/ && $2 ~/^ Explicitly installed/) { explicit = 1 }
+       }
+       END { print explicit,dependents}') )
+
+    # and if we hit an issue retrieving package information
+    if [[ ${#result[*]} -lt 2 ]]; then
+            echo "error: could not get information on $package" 1>&2
+            exit 3
+    fi
+    if [[ ${result[0]} -eq 1 ]]; then
+        # we found an explicitly installed package that relies on
+        # the original query. Add it to our array, provided it isn't
+        # the original query, as that would be useless information
+        [[ "$query" != "$package" ]] && root_packages["$package"]=1
+    fi
+    if [[ "${result[1]}" != "None" ]]; then
+        # iterate over our 'Required By:' packages
+        dependents="${result[@]:1:${#result[*]}}"
+        for i in "$dependents"; do
+            walk_nodes "$i"
+        done
+    fi
+}
+
+if [ $# -ne 1 ]; then
+    echo "error: unexpected number of arguments" 1>&2
+    echo "Usage: $(basename $0) <package-name>"
+    exit 2
+fi
+
+walk_nodes "$1"
+echo "Packages that depend on [$query]"
+if [[ -n "${!root_packages[*]}" ]]; then
+    for pkg in "${!root_packages[@]}"; do
+        echo "  $pkg"
+    done | sort
+    exit 0
+fi
+echo "  None"
+exit 1
+
+# vim: set ts=4 sw=4 et: