ar.pl: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/share/ledgersmb/bin/ar.pl - from package: ledgersmb
/usr/share/sql-ledger/bin/lynx/ar.pl - from package: sql-ledger
/usr/share/sql-ledger/bin/mozilla/ar.pl - from package: sql-ledger

You may install the required package with command apt-get install {package}

Error in other languages:
ar.pl: bevel nie gevind nie
ar.pl: comandă negăsită
ar.pl: comando não encontrado
ar.pl: commande introuvable
ar.pl: command not found
ar.pl: käsku ei ole
ar.pl: không tìm thấy lệnh
ar.pl: komanda nerasta
ar.pl: Kommando nicht gefunden.
ar.pl: kommandot finns inte
ar.pl: komut yok
ar.pl: nie znaleziono polecenia
ar.pl: níor aimsíodh an t-ordú
ar.pl: no se encontró la orden
ar.pl: no s'ha trobat l'ordre
ar.pl: opdracht niet gevonden
ar.pl: parancs nem található
ar.pl: perintah tidak ditemukan
ar.pl: príkaz nenájdený
ar.pl: příkaz nenalezen
ar.pl: команда не найдена
ar.pl: командата не е открита
ar.pl: 命令找不到
ar.pl: コマンドが見つかりません