Add a ListInstalled function

I've needed at times to list the packages that are currently listed on a system. Search("") is equivalent to that, but since we have List() which is equivalent to Search("*"), I figured this might be handy to have as well.

Author: mickael-carl

apt.go

@@ -22,6 +22,7 @@ import (
 "bufio"
 "bytes"
 "fmt"
+"log"
 "os/exec"
 "regexp"
 "strconv"
@@ -44,15 +45,29 @@ func List() ([]*Package, error) {
 return Search("*")
 }
 
+// ListInstalled returns a list of packages installed on the system.
+func ListInstalled() ([]*Package, error) {
+return Search("")
+}
+
 // Search list packages available in the system that match the search
 // pattern
 func Search(pattern string) ([]*Package, error) {
-cmd := exec.Command("dpkg-query", "-W", "-f=${Package}\t${Architecture}\t${db:Status-Status}\t${Version}\t${Installed-Size}\t${Binary:summary}\n", pattern)
+args := []string{
+"-W",
+"-f=${Package}\t${Architecture}\t${db:Status-Status}\t${Version}\t${Installed-Size}\t${Binary:summary}\n",
+}
+if pattern != "" {
+args = append(args, pattern)
+}
+
+cmd := exec.Command("dpkg-query", args...)
 
 out, err := cmd.CombinedOutput()
 if err != nil {
 // Avoid returning an error if the list is empty
 if bytes.Contains(out, []byte("no packages found matching")) {
+log.Print(string(out))
 return []*Package{}, nil
 }
 return nil, fmt.Errorf("running dpkg-query: %s - %s", err, out)
@@ -69,6 +84,7 @@ func parseDpkgQueryOutput(out []byte) []*Package {
 size, err := strconv.Atoi(data[4])
 if err != nil {
 // Ignore error
+log.Print(err)
 size = 0
 }
 res = append(res, &Package{